POPULAR OIL GEOLOGY ZIEGLER Qfarnell Hntoeraitg ffiibrarg Jitliaca, New ^atk BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND THE GIFT OF HENRY W. SAGE 1891 DATE DUE 1 iBMI) TA JNM [rUfyc^ ' i ' ! * GAVLOnO miNTKOiNU.a.A. Cornell University Library TN 870.Z66 Popular oil geology, BL ,3,,„ 3 1924 004 123 760 Cornell University Library The original of tliis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924004123760 TO MY UNCLE LEONARD KIMM THIS BOOK IS GRATEFULLY DEDICATED ^. -^:?:^-^*;tgi^.¥^ gftf^^feij.-^--. ' Prospecting Colorado OH Shale. (D. & R. G. R. R.) POPULAR OIL GEOLOGY BY VICTOR ZIEGLER Professor of Geology and Mineralogy Colorado School of Mines $2.50 POSTPAID Published by C. H. Merrifield Golden, Colorado A918 ^7'1^^f1 ^'') Copyright, 1918, by Victor Ziegler THE W. F. ROBINSON CO., DENVER. 1 "^ / \ Preface. The followiiifj pages represent an elaboration of a number of popular lectures in the geology of oil and gas. These were delivered during the past winter, in part at the Colorado School of .Mines and in part in the City of Denver, under the auspices of the Colorado State Oil Com- mission. This little book is not intended to be a general treatise on the subject of oil and gas geology. Tt is not intended for the exjierioiiccd oil geologist. It is written for the man without technical or scientific training in this branch of geology. Every attempt has been made to pre- sent in as simple language as possible the fundamental principles of oil geology, and to render these intelligible to the layman who may be interested in this subject from the practical standpoint, or for the sake of making invest- ments, or perhaps only because of a desire to add to his general knowledge. Anyone who wishes to continue his studies in this subject is referred to the treatises mentioned below, or to the author's "Principles of Oil Geology", which is now in preparation, and to which this little book is really an introduction. I have not hesitated to draw liberally on the literature of petroleum. Because of the nature of the book, and in the desire to keep it as free as jwssible from unnecessary material, I have purposely refrained from citations and acknowledgments in the text. I have used most freely the following works: Eacon and Ilamor, "The American Petroleum Industry" ; Johnson and Huntley, "Oil and Gas Production" ; A. Beeby Thompson, "Oil Field Develop- ment" ; linger, "Practical Oil Geology" ; and Cunningham Craig, "Oil Finding". Victor Ziegi.ee. Colorado School of JMines. Februarv 1.5, 1918. Contents CHAPTER I. 1 — 10 THE RISE AND DEVELOPMENT OF THE PETROLEUM INDUSTRY. Present Status of Oil Industry — Crude Oil Prices — Appli- cation of Geology — Petroleum in Antiquity — Rise of the Modern Petroleum Industry — World's Production of Crude Oil. CHAPTER II. 11 — 24 THE COMPOSITION AND PROPERTIES OF OIL AND GAS. Elementary Principles of Chemistry — Elements and Com- pounds — Atoms and Molecules — Natural Hydrocarbons — Composition of Gas — Composition of Petroleum — Specific Gravity — Distillation Tests — Miscellaneous Properties — Solid and Semisolid Hydrocarbons. CHAPTER III. 25 — 35 THE ORIGIN OF OIL AND GAS. Classification of Theories — Inorganic Theories — Cosmic Theory — Mendeleef's Carbide Theory — Organic Theories — Coal Theory — Plant Theory^ — Dual or Engler-Hofer Theory — Processes of Oil Formation — Causes of Varieties of Oil. CHAPTER IV. 36 — 39 ROCKS AND THEIR PROPERTIES. Classification of Rocks — Kinds of Sedimentary Rocks — Conglomerate — Sandstones — Shales — Limestones — Transi- tional Rocks — Formation — Stratification — Cross Bedding — Variation in Rocks — Erosion Forms. CHAPTER V. 40 — 50 STRATIGRAPHIC GEOLOGY. Tracing Outcrops — Comparing Lithological Characteristics — Use of Fossils — Evolution — Preservation of Animal Remains — Geologic History — Geologic Time Divisions for North America — Stratlgraphic Distribution of Oil and Gas. CHAPTER VI. 51 — 59 THE ARRANGEMENTS AND STRUCTURES OF ROCKS. Dip and Strike — Outcrops — Folds — Degrees of Folding — Nomenclature of Folds — Composite Folds — Faults — Normal Faults — Thrust Faults — Unconformities. CHAPTER Vn. 60 — 67 THE RESERVOIRS OF OIL AND GAS. Sandstones — Tests for Oil in Sands — Shape of Reservoirs — Limestones — Shales — Other Rocks — The Enclosing Beds of Reservoirs. CHAPTER VIII. 68 — 75 THE LAWS OF MIGRATION AND ACCUMULATION OF OIL AND GAS. Causes of Migration — Differences in Specific Gravity — Head of Ground Water — Gas Pressure — Rock Pressure — Heat Gradient — Earth Movement — Capillary Attraction — Conclu- sions — Laws of Oil Accumulation. CHAPTER IX. 76 — 82 MAPS AND THEIR USES. Topographic Maps — Geologic Maps — Columnar Section — Structure Section — Structure Map — Isochore Lines. CHAPTER X. 83 — 110 OIL STRUCTURES AND OIL FIELDS. Structure — Classification of Oil Fields on Basis of Struc- ture — Fields with Folded Structure — Fields with Monoclinal Dip — Structural Terraces — Structural Ravines — Asphalt Sealed Sands — Fields on Domes — Wyoming — Lima, Ohio — Saline Domes — Volcanic Domes — Fields on Faults — Fields on Unconformities — Colorado — De ' Deque and Rangely — Eastern and Southeastern Colorado — Summary. CHAPTER XI. 111 — 115 POPULAR FALLACIES IN OIL GEOLOGY. Not all Rocks Carry Oil — Drill Deep — "Favorable Indica- tions" — Seeps — Salt Water — Residual Deposits — Oil Shales — Oil and Gas Showings in Wells — Summary. CHAPTER XII. 116— 124 PROSPECTING AND DEVELOPING OIL LANDS. Prospecting for Areas of Petroliferous Rocks — Locating Structures — Topographic Features — Choice of Structures — Locating a Test Well — Producing Problems — Objects of Pro- duction — Spacing of Wells — Amount of Oil Available — Flow of Oil — Defensive and Offensive Methods — Offsetting. CHAPTER XIII. 125 — 137 OIL SHALES AND THEIR UTILIZATION. Oil Shales — Location — Oil Content — Green River Forma- tion — Distillation Tests — Analyses of Shale Oil — Methods of Treatment — Scottish Oil Shale Plants — Retorts — Condensers and Separators — Scrubbers — Shale Oil Refineries — Future of Western Oil Shales. CHAPTER XIV. 138 — 144 OIL INVESTMENTS. Types of Oil Investments — Wildcatting — Geology In Wild- catting — Producing Companies • — Productive Capacity — Cost of Maintenance and Production — Value of Oil — Location — Financial Status of Company — Hammond's Dont's. List oi Illustrations. Prospecting Colorado Oil Shale — Frontispiece. Figure Title Page 1. Production Chart of Crude Oil in the U. S 2 2. Fluctuation in value of Crude Oil 3 3. Map of Oklahoma 10 4. Relation of weight and specific gravity of Crude Oil 19 5. Specific gravity — weight diagram 20 6. Map of Texas 26 7. Map of Kansas 30 8. Distribution diagram of fossil form 42 9. Production chart according to age of rock 50 10. Dip and strike 51 11. Various types of Folds 53 12. Monocline 54 13. Folds represented by dip and strike symbols 55 14. Normal fault 56 15. Thrust fault 57 1 6. Effect of fault on wells 57 17. Unconformity in Wyoming 58 18. Effect of packing on porosity 61 19. Lenticular sands 63 20. Lenticular sands as shown on map 64 21. Map of Agusta and typical well log 66 22. Effect of capillary attraction 71 23. Gas, oil and water well on anticline 74 24. Ideal landscape and its contour map 77 25. Map and section of ideal dome 79 26. Application of convergence maps 81 27. Spindle Top Field, Beaumont, Texas 84 28. Oil map of the United States 85 29. Oil pool in basin, Oklahoma 86 30. Map of Volcano Springs anticline, W. Va 87 31. Idealized section through EJastern oil fields 88 32. Map of structural terrace 89 33. Map of structural ravines 90 34. Structure of oil sand on terrace 90 35. Surface structure on terrace 91 36. Oil pool in lenticular sand 92 37. Map of Wyoming, showing oil districts 93 38. Structure map of Basin Oil Fields 96 39. Structure map of Greybull Oil Fields 97 40. Structure map of Grass Creek Oil Field 102 41. Sketch map of Colorado 104 42. Saline dome 106 43. Section of volcanic neck 107 44. Section through a Mexican Oil Field 107 45. Oil pool sealed in by fault 108 Figure Title Page 46. Gas pool at unconformity, N. Y 109 47. Oil pool at unconformity, Wyo 110 •48. Oil seep and accumulation down dip 113 49. Dome left as structural piountain ... - 118 50. Dome eroded into valley 118 51. Section showing relation between width of productive area and dip of structure 119 52. Section of oil pools on unsymmetrical anticlines 120 53. Flowing well. Salt Creek 122 54. Offsetting 123 55. Map showing Western oil shales 126 56. Outline of treatment of oil shales 127 57. Experimental oil shale plant 130 58. Oil shale retorts 132 59. Bench of oil shale retorts, Pumpherston, Scotland 133 60. Bench of oil shale retorts, Broxburn, Scotland 134 61. Shale oil refinery, Broxburn, Scotland , 136 62. Production curves of wells 142 WS.S. WAR SAVINGS ST4MPS ISSUED BY THE UNITED STATES GOVERNMENT I. The Rise and Development of tne Petroleum Industry. Present Status. The rise and develapment of the petroleum industry is one of the interesting industrial rdinances of the present day. Starting with an insignificant beginning of two thousand barrels in 185U, the production of the United States has risen to a total of ;3()(),()00,()()i» barrels for l!tl6, a figure so large that it is difficult to form a conception of its magnitude. Collected in one spot the oil would form a lake five feet deep, covering an area of thirteen square miles. The value of the crude oil may be roughly esti- mated at $500,000,000. Large as this figure is, it does not correctly represent the magnitude of the petroleum in- dustry. Thus, for the year 1917 the value of the refined products will greatly exceed $1,000,000,000, a value greater than the combined value of the production of gold, silver, copper, lead, and zinc, for the same period. This is in spite of the excessive high production of the last three products for war materials, and their corresponding high value. The accompanying chart shows graphically the pro- duction of crude oil in the United States since 1S59. While production has increased from 250 million barrels in 1913 to :!50 million barrels in 1917, consumption has increased much more rajjidly. It is estimated that consumption has doubled in the last four years, and now exceeds production by nearly 15 percent. This excessive consumption causes serious concern, es- pecially because our known oil fields are rapidly nearing ex- haustion. Thus the United States Geological Survey gives 1 2 POPULAR OIL GEOLOGY. the following estimates as of January 1, 1917, to show the percentage of exhaustion of the various oil fields : Ohio, Indiana 93% Appalachian 70% Illinois 51% Oklahoma, Kansas . .25% California 26% y^arj ^SVO /SOS /9/0 Figure 1. Chart showing graphically the production of Crude Oil in U. S. since 1859. POPULAR OIL GEOLOGY. 6 The total estimated production of the United States since isc>d is four billion barrels; the total available sup- ply is Pf'vcH billion, six million barrels. At the present fiite (if consumption, this is sufficient for fmly about twoiity years. As a result of this condition the value of crude oil is higher than it has ever been before, in conse- quence of which there has been intense interest in oil stocks, both for investment and for speculation. Hundreds ms ivii tmr - — « — < -- ^ 1 . . n /* 'jmf « -^ ^ ^ 1 H'T' Cte. 10W \-K V^lA ■ 1 - ■— . - - -• --H ' L w* Of ~ " - ---< ^ - — 1 _ lu. ^ VLT (^ ' --■ - - - - - - - - — ^-^ — C IfiW " - — — - - - "- - z '—i d ' — 1 — i 1 — 1 ^ 1 — : _ ^ 1 1 Figure 2. Chart showing fluctuations in the value of Crude Oil for the prominent American oil fields. Each horizontal divi- sion indicates three dollars. of new oil companies have been organized, mostly for the purpose of exploiting or prospecting for new fields. Another result is the elimination of wasteful methods formerly characterizing the oil industry. Engineering and scientific methods are adopted, both in production and re- fining. Among all of these the most important is the general appeal of the oil man to the geologist. 4 POPULAH OIL GEOLOGY. The Application of Geology. In the early days of the oil industry, drilling was carried on in an unsystematic manner, without any re- gard for geological features. The presence of salt water, of oil and gas seeps, which experience has often shown to be delusive, were considered indications favorable enough to warrant extensive drilling campaigns. As a matter of fact, there was a marked distrust shown toward the geolo- gist. This was not surprising, because in general the geologist followed the oil man and did not precede him. It remained for an American geologist, I. C. White, in 1885, to give us the first clear outline of the application of geological methods to the finding of oil and gas fields and to the locating of wells. Indeed while geologists had been active before his day, they had not recognized the fact that geology could actually be used for this purpose. When White announced his discovery, it was received with derision by his own colleagues, who were only convinced when its practicability was actually demonstrated. Practical men remained skeptical, and only the serious condition of the oil industry in the last few years, and a consequent employment of geologists in large niim- bers, with the results they have achieved, convinced them that geology is indeed far more important than the most enthusiastic thought. It has been estimated that, in 1913, only three geologists were employed in the Kansas-Okla- homa fields. Today, in the same field, two hundred and fifty are employed. As a result of their labor, the chance for success of wildcat, or prospect wells has been reduced from one in one hundred and fifty, to one in three. Vir- tually every large oil company of importance maintains a geological staff, the duties of which are to prospect for new favorable areas, to locate test wells, and to map out a drilling campaign insuring the most economical produc- tion and maximum yield from a given field. The value of geological services are attested by the success of many new companies to such an extent, that it has become generally recog-nized that a disregard of geo- logical conditions is virtually an assurance of failure. POPULAR OIL GEOLOGY. 5 Petroleum in Antiquity. Ill the introductory remarks, the petroleum industry was said to bo about fifty years old. Its extreme youth is vprv surprisinj;-, because oil and its products had been known for many centuries and were used Inufj before the Christiiin era. Antiquarian explorations in Asia ]\[iiinr and T\i;;y])t have proved that asphalt was generally used in place of mortar for building purposes. Herodotus iiicu- tions that the walls of Babylon and of Xinevah were so constructed. According to the Old Testament asphalt was also used in the walls of the Tower of Babel. The ancient civilization of the Tncas in Peru, and ni tl:e Aztecs in Mcxicf) employed asphalt for architectural purposes. The Old Te.sliiiiient also mentions tlie fact that llic .\rk of JS'oah and the woven basket of Moses were made waterproof by an npi)lication of oil. Among the I'lgyptians, oil was used in enihalmiiiL;:. Indeeil, the word "iniiininy" is said to lie derived from the term "mumiya", the Persian for asphalt. Records show that since time immevnorable, oil has liccn used for lighting in the cities of the Red Sea, as, for example, Ras Gemsah and Oebe] Zeit. The medicinal value of oil was recognized by the Indians long before white men set foot on America, llarco Polo, writing in the thirteenth century, relates that the Russians of the Baku region, on the Caspian Sea, drank oil, both as a cordial and as a medicine. As a matter of fact, modem investigations pi'ove that the Persians sought the oils of Baku centuries before the Russians occupied the Caucusus. In view of these many uses, it is perhaps natural that oil and gas should become objects of worship. Most famous wei'e the ''Kterual Fires of Surakhani", on tlie Aspheron peninsula in the Caspian Sea. Here were the sites of sacred shrines and temples, to which the Parsees, or fire- worshipers, conducted pilgrimages, recorded as far back as 600 B. C. .\ modern Hindu temple, about two hundred years old, marks the site of the ancient shrines. The "Eternal Fires" are really gas seeps which, once ignited, will continue to bum. b POPULAE OIL GEOLOGY. Rise of the Modern Industry. The first elementary and crude attempts at the pro- duction of oil on a large scale were made by Peter the Great, in 1723. He, at that time, granted a private monopoly for oil production in the Baku region, which, it is interesting to note, continued in force to 1872. The real pioneer in oil production, however, was the United States. The first record of oil in America dates back to 1627, when the Franciscan friar, Joseph de la Eoche d'Allion, described in a letter the oil springs of Allegheny County, iN'ew York, which were highly prized by the Indians. Oil received only passing attention in the early part of the nineteenth century. There was, how- ever, great interest in salt and natural brines, which led to the devising of methods for drilling wells. The first drilled well in the United States was sent down in 1806, on the bank of the Kanawha River, in Virginia. This well was eighty feet deep and produced, in addition to salt water, about twenty barrels of crude oil a day. In 1820 drilling methods were so perfected that it was possible to drill wells one thousand feet deep. The general demand for salt and brines resulted in the drilling of a great num- ber of wells along the Kanawha. A great number of these produced oil, which was considered obnoxious and was permitted to flow into the river. From this practice origi- nated the name of "Old G-reasy", by which the Kanawha River was known for many years. During this period a small trade was established which exploited the use of oil for medicinal purposes. It was generally advertised as a cure-all, guaranteed to alleviate and cure all the ills of the human body. Especially famous were the so-called "Seneka Oils", and Krier's Petroleum Rook Oil. Krier was a druggist in Pittsburgh who had an excess production of crude oil beyond that needed for medicinal purposes. He therefore erected a homemade still and refined oil, selling the light products for illuminating purposes. During this period natural oil had to meet the competition of the coal- oil industry, which was based on the distillation of illumi- nating oils from coalsr Indeed the common term "coal-oil", POrULAR OIL GEOLOGY. 7 for kci'dsciic, is a survival of this industrv. In the early part I it tlio nineteenth century it was thought that the sup- ply of crude oil was apparently insufficient and was too spasmodic in its occurrence to insure i'x(cnsivc commercial use. A few people, hnwcAcr, had faith in the possibilities of the natural oil and, in 1S54, organized the first oil company of America, "Th(^ Pennsylvania Rock Oil Co." Like mniiy nf its successors, this company became involved in financial difficulties and was reorganized in Is.^s as tlie "Seneca Oil Co." This company secured Col. E. L. Drake ns su|icriiit('iid('nt of field o]K'r:itioiis, who drilled tlie first well in 1S,M», at Titusville, Pennsylvania. At a depth of fifty-oif;ht feet a flow of oil of twenty-five barrels a day was encountered. Drake's well marks an epoch in the his- tory of petroleinn hecause it was the first well drilled for the purpose of securing oil. The well demonstrated the feasibility of drilling for oil. It therefore insured the rapid develo])inent of the petroleum industry and at tlie same time paralyzed tlie coal-oil industry, then at its climax. Vigorous drilling followed all along the Allegheny River, spreading eventually into Ohio, West Virginia, In- diana, and TvTew ^'ork, and resulting in the development of the Appalachian oil fields, for maiiy years the leading producer in America. The chief competitor of the Appalachian field was the Baku region on the Caspian Sea. ITere the first well was drilled in issi) and prc)\ed such a lie ivy producer that the news, which exceeded the most s;inguine expectations, was regarded with suspicion for many years. The develoipment of oil fields proceeded slowly be- cause the progress everywhere was hindered by lack of transportation facilities. Thus both in the American and Russian fields the oil was hauled in carts to the railroad stations. The first pi]ie line of importance was laid in IsT.'i from the oil country to Pittsburgh. Russia quickly adopted tliis convenient method of transportation. As may lie imagined, the carters vigorously opposed pipe lines and went taraffin base; those of Texas and California are asphalt base. Those of Illinois carry equal proportions of both and therefore are known as mixed base oils. Although oils are essentially compounds of car- bon and hydrogen ; sulphur, nitrogen and oxygen are also present, as well as other impurities of minor importance. In percentage composition, petroleum shows the following extreme ranges : Carbon, 79% to 88% Hydrogen, 9.6% to 14.8% Nitrogen, 0.02% to 1.1% Sulphur Trace to 4% 18 POPULAE OIL GEOLOGY. Sulphur may be present as free sulphur, or it may be present as a sulphide. In the latter case it imparts to the- oil a very disagreeable odor, that of decomposing eggs, which is characteristic of the oils of Ohio and Texas. Nitrogen is present in the form of complex organic com- pounds. These are frequently edible, consequently such oils, as for example certain oils of California, when ex- posed to the air, become quickly infested with maggots. Analyses of Petroleums. C H S N Findlay, Ohio 83.41 13.13 0.56 0.06 Oil City, Pa 85.80 14.04 Baku, Russia 86.25 13.48 Beaumont, Texas 85.05 12.30 1.75 Ventura, Calif 84.00 12.70 0.40 1.70 McKittrick, Calif 86.06 11.45 0.87 Alsace, Germany 79.50 13.6 6.90 (Oxygen S N) Rangoon, Burma 83.80 12.70 3.35 Java (DanDang-Ho) 87.10 12.0 0.9 Burning Springs, W. Va. . 84.3 14.1 1.6 Amaze, Japan 84.66 13.22 0.22 0.36 Specific Gravity. The weight of crude oils is dependent to a consider- able extent on the chemical composition. Paraffin base oils are ordinarily the lighter. Consequently the expres- sions "light" oil and "heavy" oil have been used as syn- onymous with paraffin base and asphalt base oils, respect- ively. The relative weight of oil as compared with the weight of an equal volume of water is known as specific gravity. Considering the specific gravity of water to be one, oil lies between the limits of 0.Y3 and 1.0. It is more customary to express the M'^eight of oil in terms of degree of the so-called Beaume scale. This is usually read direct on a hydrometer immersed in the oil. The degree of Beaume goes up as the weight goes down, therefore a light paraffin base oil has a high degree Beaume', or is said to be a high gravity oil. A heavy asphalt base oil has a low degree Beaume, and is said to be a low gravity oil. The appended table shows the relation existing be- tween the degree Beaume, the specific gravity, and the POPULAR OIL GEOLOGY. 19 B" Gal fori Barrel F Gr. eSlion Barrel lO oooo asze 349 73 62.30/ 45 .eooc 6.66 3 zra.as 49.84 1 1 1 rsas S Z69 3-47 3/ 61 8S-9 4- 12 .»a5^9 8 Z 1 1 S'f-f 86 61. -422 4T .79/0 6588 276.6 8 •49.280 (3 .079O 8.IS3 3-42.-*« 60003 4-a .786S 6s5o 275 1 1 48.999 1* 97Z2 B OST' 34007 60 569 4.9 .7821 6.514 ZTSST 48T26 IS S&55 Sd*' 3 37 72 6e 152 5-0 .7778 6478 272 07 48458 16 0«83 7- 986 335:^2 SrST'tC) SI .7735 6.442 ZTO S& -48. ISS IT .052-» T03 2 333 )<^ ffesss se. .7692 6 4o« Sf,e.oA 4T9Z2 <8 S'^SS r era ,330. 87 SB.9SI S3 .7-650 6 871 zd-rsa 4T660 • 3 S3Se y.Bzs saa.6 7 5BSSa S4 .76 o9 6 3S7 266 /6 4T.405 zo .3333 T.rTS 326. -tS s-e./'/s S5 Tsse £303 £64. 72 4T 149 21 92TZ 7-.72S 3S-4.3 3 S-rras S& .7527 6 2«9 269 29 46 894 as sail 7 67/ 322 19 57 385 S7 .7487 6S35 2a/.a9 46 644 25 9lSO 7.CiO 320.O6 ffT-ooS 58 .744 7 6 202 2 60.'»3 46 305 z^ .909I 7 STI 3/7 93 6 6 637 S3 .740T 6 163 2 53 03 4-S I4S zs 9032 TSZ-Z 3/5". S3 S6.z-ro 60 .7363 6 /9& 257 TS 45.30J Z6 SST-* 7-47^ 3/3. So se&os <3/ .T3SO 6./05 2 56 40 45 667 i.T .9917 7-42S 3//'3 / ss^^ss^ 62 7292 6 OT3 ZSSor 45:-429 2S .9861 7 S79 309.3S ^s-.zos 63 7254 6.04/ 25374 45.193 29 B8oS 7 333 30799 5+856 64 '7216 6 009 zse.'^i 44.95e 50 e7SO 7287 306 07 5*513 65 .7/73 5" 379 251. 12 4-4.726 3t .S6Si, 7.Z-*Z SO* IS S'f/TT 66 .7/4 3 S-349 2 49 86 44 502 32 .86*2 T.I9T S02 23 53.840 67 .T/07 S" 9/9 248.53 44.277 39 SS99 r ISS 30O.-4-4 SS5IO 68 .ro7/ 5-883 247 34 44.053 a-t .8S3T 7/10 2 9S.6S 53/86 69 .TO 35 5:359 246.oe 43 829 35- &*es- Toss 2ss.ao SZ.B6Z 7o .7000 5-829 2-44.a5 4361 1 36 .BtA'f 702-* ass'.a^ SSS^S 71 .£96.5 5SO/ 24 3 63 49 393 sr asas «eS2 2 9S.e3 5i.«2.r 72 .693/ 5'772 242.44 43 ISI 3S 89A3 6.940 29/. ta 51 9/S 73 .6 897 5:744 241. 25 4 2.969 33 . Bza* 6eei» 289.77 SI.&IO 74 .6863 5:7/6 a4o 06 42737 '»o .8235 s.qsa 288 OS SI SoS 75 .6829 5:687 2 38. 87 -^2545 't 1 .8/87 6.S1S 2 86 38 SI. 006 76 6796 5:660 2 37 72 42.333 •»a .ai-»o 6.778 2e'»73 So.-ri 3 77 6763 .5:632 236. 36 42.134 -♦3 .So92 6 7»9 2830S- « 0. -»/■»■ 78 .6731 S.606 235.-45 41.935 ■^•^ .80+6 6.70( 28/ ■4'4 ^oiar 70 .6699 SST9 2 34.33 -11.7-35 Figure 4. Table showing the relation existing between specific gravity and weight of oil. (Payne & Stroud) 20 POPULAR OIL GEOLOGY. POUNDS pen CUBIC foot tjoiivs KA/ saf^nod POPULAR OIL GEOLOGY. 21 weight of crude oil. The second table shows the specific gravity of a few typical oils. Specific Gravity of Typical Oils. Sp. Gr. B6. Pennsylvania 0.801 —0.817 46.2 — 42.6 Ohio 0.816—0.860 42.8 — 32.5 Kansas 0.835 —1.000 38.8 — 10.0 Colorado — Boulder 0.814 42.0 Debeque 0.809 43.0 Shale Oil 0.9138 23.0 West Virginia 0.841 — 0.873 37.6 — 30.0 California 0.920 —0.873 30.0 — 12.3 Dutch East Indies 0.765 —0.791 53.0 — 47.0 Peru 0.815—0.945 38.0 Roumania 0.736 —0.8894 27.0 — 60.0 Mexico 0.809 —1.000 43.0 — 10.0 Wyoming — Greybull 0.786 48.2 Grass Creek 0.8187 41.0 Grass Creek 0.7984 45.3 Byron 0.8174 42.0 Cody 0.8454 35.6 Salt Creek 0.8221 40.3 Salt Creek 0.8255 39.6 Shannon 0.910 24.0 Lander 0.9198 22.2 Lander 0.9126 23.4 Lander 0.9091 24.0 Plunkett 0.8121 42.4 Pilot Butte 0.875 30.0 Distillation Tests. The percentage of the various products yielded on refining is most frequently used as a basis for comparing the different oils. Refining is simply a distillation pro- cess in which the oil is heated in retorts at various tem- peratures and the volatile material driven off and con- densed. The very volatile matter is given off at low tem- peratures, the less volatile at increasingly higher tempera- ture. The final residue is known as the base. This may be commercially valuable paraffin, as in the case of light (lil.s, or an oxidized residue, Avhich we call asphalt. A distillation analysis shows ordinarily four or five products. 22 POPULAE OIL GEOLOGY. First, tlie volatile oils, which include gasoline, naphtha, and benzene; second, the illuminating oils, or kerosene; third, the lubricating oils; fourth, fuel oils, which are of chief importance in the asphalt base oils; and last, paraf- fin, if present in commercial qiiantities. The following table gives the result of distillation tests on a few typical American oils: 1 2 3 4 5 6 Volatile Oils 12.0 11.5 3.5 11.0 3.0 6.0 Illuminating Oils 67.0 43.0 39.0 41.0 15.0 18.0 Lubricating Oils 12.5 15.0 ... ... 6.0 1.5 Fuel Oils 4.0 25.0 56.0 45.0 73.0 72.0 Paraffins 2.0 2.0 ... ... 1. Appalachian 4. Oklahoma 2. Lima, Ohio 5. Texas — Louisiana 3. Illinois 6. California Distillation Tests of Wyoming and Colorado Oils. Volatile Oils . .31.0 Locality — Greybull, Wyo Basin, Wyo Basin, Wyo 26.0 Basin, Wyo 30.5 Grass Creek, Wyo. 22.0 Grass Creek, Wyo. 35.0 Cody, Wyo Cody, Wyo Byron, Wyo. . . . Salt Creek, Wyo Salt Creek, Wyo Shannon, Wyo . . Shannon, Wyo. . Lander, Wyo... Lander, Wyo . . . Plunkett, Wyo . . Pilot Butte, Wyo Douglas, Wyo . . Douglas, Wyo . . Rangeley, Colo. Rangeley, Colo 25.0 De Beque, Colo. . . 1.0 De Beque, Colo Boulder, Colo 20 — 22 Florence, Colo. . . 4.15 29.0 8.0 11.0 2.5 2.0 14.0 19.0 8.0 Illumi- nating Oils 32.5 22.5 34.5 38.0 42.0 32.0 37.0 48.0 42.5 38.0 34.0 12.5 10.0 22.0 23.5 41.0 59.0 38.5 6.0 60.0 45.0 42.0 27.0 38—40 30.45 Residue 36.5 77.5 39.5 31.5 36.0 33.0 59.6 52.4 28.5 49.3 54.0 86.9 86.6 69.9 41.1 22.0 53.5 27.0 56.5 70.9 40.0 65.4 Gravity Paraffin Be 48.2 27.5 39.5 45.6 41.0 45.3 35.6 38.0 41.0 4.97 40.3 5.56 38.4 1.14 23.9 24.1 22.2 0.91 23.4 ' . . . 42.4 30.0 2.00 35.9 20.4 20.00 43.6 37.8 25.6 POPULAB OIL GEOLOGY. 23 Miscellaneous Properties. The color of oils is variable and depends mainly on composition. Paraffin base oils are the lighter; yellow to brown by transmitted light, green by reflected light. Asphalt base oils are ordinarily dark brown to deep black in color. The odor of certain oils is quite characteristic. The oils of Pennsylvania and Wyoming have the odor of gaso- line. California oils have a pleasant aromatic odor. The nil of the East Indies has the odor of oil of cedar. Ohio, Indiana, Ontario, and much of the Texas oil has the unpleasant odor of hydrogen sulphide. Another property of importance is viscosity, which may be defined as the internal resistance offered to flow. ParaflSn base oils are ordinarily quite fluid. Asphalt base oils are viscous. "Viscosity has quite an important effect on the transportation of oils. Some oils flow with such reluctance that they must be heated before they can be pumped tliroiii>li a ])ipe-liue. Oils that remain fluid at temperatures of about 0°, are known as winter oils. Those wliicli remain fluid only at temperatures of 40 degrees or higher, are summer oils. Summer oils are the heaviest oils, with high viscosity, which can onl}' be shipped during the summer season. Other physical properties, such as surface tension, optical aclivity, refraction, and expansion upon heating arc frequently determined. They, however, possess only a slight practical value and are more important from the theoretical standpoint; hence they will not be discussed in detail. Solid and Semi-Solid Hydrocarbons. There are other natural hydrocarbons besides gas and oil. As a matter of fact, all gradations, both chemical and physical ma^' be found from natural gas through oil into viscous and even solid bodies. A few of these deserve special mention. A viscotis pasty black-colored hydro- carbon, representing the resklue from evaporating heavy 24 POPULAE OIL GEOLOGY. oil, is knp'Wn as "maltha" or "chapopote". The natural wax or paraffin, ordinarily the result of evaporation of high-grade oil, is known as "ozokerite". "Gilsonite" and "grahamite" are very valuable, brilliant, black-colored, solid and brittle hydrocarbons, useful chiefly for varnishes,- shellacs, and enamels. "Lake asphalt" is known only from the Island of Trinidad, and is a highly viscous, semi- solid substance, similar to common asphalt. Occasionally the pores and openings in rocks are com- pletely saturated with residues left by the evaporation of oils. Such rocks are known as "bituminous rocks". Sand- stones, shales, and limestones, as well as gravels of this sort are knoAvn and are used quite extensively for road metal. III. The Origin of Oil ana Gas. Two questions are involved in any discussion of the origin of natural hydrocarbons. The first one con- cerns the original materials from which oil and gas are derived ; the second deals with the manner and methods by which this material ultimately changes into oil and gas. The first question is fundamentally a geological one ; the second is essentially a chemical and physical one. Classification of Theories of Oil Origin. The nature of the original materials from which the hydrocarbons are formed is a much disputed question. In general, all theories of origin fall in one of two classes, which for convenience we may call "inorganic theories", and "organic theories". Those of the first class maintain that the hydrocarbons are derived from inorganic materi- als. The second class, on the other hand, maintains their derivation from the remains of plants and animals. Inorganic Theories. The older and more strictly chemical theories postu- late a derivation from inorganic substances. Some of these theories are very crude and purely speculative. Others are more refined, and are based on exhaustive lab- oratory work and synthetic experiments carried on by Rus- sian and French chemists. Although there are a number of inorganic theories, attention will only be called to two representative ones. Cosmic Theory. One of the older ideas was that both oil and gas were constitiaents of the original nebular matter from which our solar system was formed; that, as the earth cooled down from high temperatures, the oil was precipitated as rain, was disseminated through the rocks, and was subse- quently collected in reservoirs to give us our oil fields. This theory, also known as the "Cosmic Theory", is an 25 26 POPULAR OIL GEOLOGY. * ** ? N tS 55 5 S I'OIMI.AE OIL GEOLOGY. 27 example of the purely speculative type, which has abso- lutely no scientific foundation behind it. Mendeleef s Carbide Theory. As an example of the more refined chemical theories we may mention tho theory of IMendeleef, who presup- poses the existence of metallic carbides in the interior of the earth. (Metallic carbides are compounds of a metal and carbon, similar to the calcium carbide which is used extensively for the generation of acetylene gas.) These carbides, at high temperatures in the interior of the earth, react with water to form acetylene, just as this gas is pro- duced in our commercial carbide plants. Subsequently, when subjected to different degrees of heat and pressure this acetylene is changed into the various hydrocarbons found in Nature. Inorganic theories are more generally accepted among chemists than among gcnlof^ists. Eugene roste, a Cana- dian geologist, however, is the most vigoroiis advocate of this view, and cites the following facts among others, which he believes definitely proves that oil is derived from inorganic materials : 1. Hydrocarbons have been found in meteorites. 2. Hydrocarbons have been found in the spectra of the stars and nebulae. 3. Hydrocarbons have been made artificially in the labnrattiry from inorganic materials. 4. They havo been found in igneous rocks, in veins, and in volcanic emanations. 5. ]\linute quantities have been found in cast iron. It may be of interest to add in this connection that there is a strong probability that the oil that occurs in igneous rocks and in volcanic emanations is derived from some oil-bearing rocks imder the earth's surface, and con- sequently not inorganic. In any attempt to discover the origin of petroleum, we must carry in mind the fact that the question at issue is not "How may petroleum be pro- duced", but "How can commercial a c cum illations of oil be formed ?'' Although all geologists are willing to admit 2,8 POPULAR OIL GEOLOGY. the possibility of oil formation from inorganic materials, by far the greater majority deny the probability of pro- ducing large quantities in this way. There is absolutely no evidence to show that the oil of any commercial field is derived from inorganic sources. Organic Theories. There are a number of different theories which post- ulate the derivation of hydrocarbons from the dead re- mains of organisms. Five such groups of theories are worth specific mention, all of which differ in that they start with different organic materials. These postulate one of the following as original materials : 1. Coal and similar carbonaceous matter. 2. Accumulation of plant remains. 3. Accumulation of animal remains. 4. Oozes, muds, and slimes made up in large part of the remains of micro-organisms. 5. Plant and animal remains in combination. Within the limits of this discussion, it is impossible to treat all of these in detail. Several of these theories may be selected as most representative, and will be briefly described : Coal Theory. The oldest of the organic theories postulates a deri- vation of oil from coal fields, and is suggested by the associa- tion of coal and oil in the older known fields. It is also a fact worth noting that certain of the gases which escape from coal and which are often so dangerous in mines are similar in composition to the hydrocarbons in oil fields. Again, it is possible to distill from coal, at high tempera- ture and pressure, certain gases and oils, indistinguishable from those met in Nature. In this connection attention has already been called to the derivation of the word "coal oil", which is used synonymously with kerosene, and which emphasizes the fact that illuminating oils were originally manufactured from coal. In several localities, as for ex- ample, in Scotland, at Vendee in France, and on the POPULAR OIL GEOLOGY. 29 Island of Trinidad, oils may be seen oozing out of coal beds. In recent years, however, a great number of oil fields have been found which show no relation whatever to coal fields, and which consequently throw discredit on the idea that all oils are derived from coal. In a few cases the theory is capable of application, and at least tentatively established. Plant Theory. There are many modifications of the theory which postulates a derivation from plants. Probably the one best established states that gelatinous plants, such as algae, are most likely to give oil under favorable conditions. In- deed, all our knowledge of the chemical principles in- volved lead us to the belief that plants with hard, woody tissue are more likely to yield coal rather than oil. The adherents of this theory believe that the accumulated re- mains of gelatinous plants forming along the ocean shore, are buried under the mud and sand, accumulating there, and are protected in this way from decomposition. Sub- sequently those remains are distilled into the various gases and oils met in Nature. In the laboratory, it is pos- sible to distill oils from such plant remains. Geographic study proves that such plants accumulate in considerable abundance. Therefore the probability of such' origin must be granted. As a matter of fact, certain of our oils very high in paraffin, such as the oils of Pennsylvania, are probably of this derivation. Engler-Hoefer or Dual Theory. The strict vegetable origin cannot explain all oils. Thus the many oils, high in nitrogen, sulphur, and with an asphalt base, can probably not be derived from plants alone. On the other hand, there are many objections to the theories which attempt to explain the derivation of oil and gas from animal remains alone. Thus, for exam- ple, it is necessary to dispose of virtually the entire nitro- gen content and preserve at the same time the fat of the animal. The abundance of scavengers in the ocean which POPULAR OIL GEOLOGY. 31 si C t S r POPULAR OIL GEOLOGY. 31 will, under ordinary conditions, devour the dead bodies of all animals, is often cited as another objection against this theory. Because of these reasons the so-called "Dual- theory" has been developed which postulates a derivation of oil and gas from both plant and animal remains. ProV ably the greater number of geologists favor this view, at the same time emphasizing the relatively greater import- ance of animal remains as a source of oil. It is believed that the decay of dead plants and animals is retarded by the salinity, or perhaps coldness, of the ocean water at the time of accumulation, and that there is a sort of select- ive putrefaction followed subsequently by burial. As a result of later distillation our oils are formed. In this connection it is of interest to note that a number of differ- ent chemists have succeeded in making oils from mixtures of plant and animal remains in the laboratory, which were in every respect similar to natural oils. Tliat the animal theories are fully competent to meet all the requirements of conniiereial oil fields is certain, in spite of the greater liability of the rapid decomposition and of being cnten by scavengers. Thus it has been esti- mated that the annual catch of licrring in the Xorth Re:i for l.SOO years is sufficient to yield all the oil produced in Galicia. If we carry in mind the fact that the annual catch of herring is only an insignificant fraction of the total number of herring in the North Sea, and that the herring tliemselves represent an infinitesimally small por- tion of animal life in the oceans, the fact becomes appar- ent that the most insignificant fraction of life forms only need be preserved to give us all the oil we find in Nature. It is certain that the organic origin of oil is best supported both by the geological evidence and by the chemistry of the hydrocarbons. Animals are probably the most important source. There is no evidence to show that any commercial oil fi.eld derives its oil from inorganic materials. Processes of Oil Formation. In the preceding discussion we have come to the con- clusion that organic matter represents the raw materials 32 POPULAR OIL GEOLOGY. from which petroleum is produced. We shall now discuss the manner and methods by which these have become con- verted into the different kinds of oils. A great deal of experimental work in the synthesis of oil has been done by chemists, much of it, however, under conditions not found in Nature. As a result a number of false ideas have been advanced and have gained current acceptance. Rea- soning and work along this line should be based on condi- tions as determined by geological observation. Thus we know: 1. That the formation of petroleum is a general process. 2. That the original materials represent both animals and plants. 3. That the process of alteration is one of selective putrefaction and distillation, taking place under the fol- lowing conditions : a. At comparatively low temperatures. b. Under comparatively great pressures, e. In the presence of water, usually salty, d. During a great space of time. The temperature under which the alteration takes place can be determined roughly by the depth of burial of the oil rock. There is every reason to believe that this probably never exceeds 300 degrees Centigrade. The pres- sure is at least partially due to the weight of the over-lying rocks, and in most cases is probably not less than one ton a square inch. Causes of Varieties of Oil. In the preceding discussion we have called attention to the fact that there are different kinds of oils in Nature, such, for example, as parafSn base oils, asphalt base oils, oils high in sulphur, or high in nitrogen. A number of explanations have been advanced to account for these varie- ties. These may be tabulated as follows: POPULAS OIL GEOLOOir. 33 1. Difference in the original organic material. 2. Physical conditions at the time of formation. 3. Migration and resulting filtration of oil. 4. The age of the oil. A number of American geologists believe that the character of oil depends upon the nature of the original organic material. They believe that high-grade paraflSn oils are derived from gelatinous plants; that asphalt base oils are derived from animal remains; that the high per- centage of nitrogen and sulphur present in certain oils indicates also animal origin. A larger number dissent from this view and believe that physical conditions or the age of the oil will determine "its character, and that the same type of organic material may give all the varieties of oil we have, depending upon physical conditions at the time of formation. Thus there is much evidence to show that high pressure means the retention of volatile con- stituents and a light oil. High temperature means a rapid formation of oil and a production of much asphalt Low heat means a slow gi-adual change with the production of parafiin. There is good reason for the belief that oil is seldom retained in the place where formed. Ordinarily it has migrated through the rocks and become entrapped subse- quently in a reservoir. In moving through the earth's crust, oils seep through various kinds of rock, all of which may exert some influence. Thus oils traveling througli clays are separated into two portions, a light oil, which percolates through the clay, and a heavy residue which is retained. That this process is active in Nature is certain. Another explanation is based on the fact that there are a definite series of stages in the alteration of organic matter to oil ; that the older oil is the better, and that the older oil retains the greater proportion of gas. The fol- lowing table shows in graphical manner the stages in the alteration of fats and waxes into oil. 34 POPULAR OIL GEOLOGY. Animal and Vegetable Residue. (Fats and Waxes) Liquid Paraffins and gases (C H , ) n 211+2 Liquid Parafllns and gases (CnH,„+2) defines Polyolefines (C„Hn)x Solid Paraffins Liquid defines Naphthenes Paraffins (C H ) (C H ) Naphthenes (C„H„J Lubricating Oils Liquid Paraffins and gases (C,H^n+2> Naphthenes (C„H^„) Lubricating Oils (Low in Hydrogen) C„H.„ .) The table shows that the first products of distillation of fats and waxes are stable paraffins and defines, and unstable solid paraffins. The solid paraffins produced, break up into liquid paraffins and naphthenes, both of which are stable and remain unaltered, while the defines pro- duced from the original fats and waxes as well as from the solid paraffins, break up into poly-olefines, which in turn are distilled to form liquid paraffins, naphthenes, and lubricating oils. As in the case of the first distillation, the liquid paraffins and naphthenes remain unaltered, but the lubricating oils break up to form more of the light par- affins and naphthenes, and in addition relatively stable lubricating oil, low in hydrogen. To summarize, we may conclude that the varieties of oils may be caused in part by differences in the material POPULAR OIL GEOLOGY. 35 fniiii which tlicy are formed, and in greater part they may rrprcseiil the result of alteration of the same material un- der different conditions. High temperature and conse- quentl}' rapid alteration means a heavy asphalt base oil, cliicfly useful as fuel. F.ow temperature, high pressures, slow alteration, old age, and much migration result in high- f;-nido light oil, pxtreniely valuable because of the high ]iro|yirti()n of gasoline and other volatile constituents re- tained. IV. Rocks anci Tlieir Properties Classification of Rocks. Geology as applied to petroleum work is concerned with the different kinds of rocks and with their arrange- ment in the earth's surface. It is customary to divide all rocks into three great classes, known as "igneous rocks", "sedimentary rocks", and "metamorphic rocks", respec- tively. The igneous rocks represent those that have solidified from an originally molten condition. They may reach the earth's surface like the lavas flowing from volcanoes, or they may harden deep below like granite. The sedimentary rocks represent materials deposited in layers by the action of the waves, of the wind, or of ice. In small part they also represent materials deposited from solution. They accumulate most commonly under water in oceans, seas, lakes and rivers. The metamorphic rocks were originally igneous or sedimentary rocks that have been so acted upon by heat or pressure subsequently to their formation, that they have lost their original characteristics. Both meta- morphic and igneous rocks are frequently included under the term "crystalline". In physical characteristics they are quite compact rocks, ordinarily very hard, and crystal- line in structure. They never carry commercial accumu- lations of oil. Kinds of Sedimentary Rocks. We recognize four kinds of sedimentary rocks; con- glomerates, sandstones, shales and limestones. Conglom- erates are gravels consolidated into rock; Sandstones, as the name implies, represent consolidated sands ; Shales are hardened and consolidated muds and clays; while Lime- stone represents the accumulations of the hard parts and shells of various marine animals, such as, corals, oysters, and other shell fish. POPULAR OIL GEOLOGY. 37 Conglomerate. Oonglomerate ordinarily represents the coarse mate- rial deposited along the edge of the ocean shore. It con- sists of boulders of various sizes cemented to a greater or lesser degree. The boulders and pebbles are usually well worn and rounded. Rocks made up of angular fragments instead of boulders are known as breccias. Conglomerates are of minor importance in oil fields. Sandstones. The sandstones are chiefly made up of grains of the mineral quartz. A cement of oxide of iron gives the rock a color varying from pale yellow to a deep red or brown. Lime, or calcium carbonate and silica form the common cement of the white sandstone. Shales. Shales are very compact rocks made up of exces- sively fine-grained material, especially mud and clay. The shales, to a greater degree than sandstones and con- glomerates, show a well-defined bedding. Their most char- acteristic property is to split in thin,, paper-like sheets. Oil-bearing shales are dull in color. Black, dark gray, or dull brown are the most common. Bright-colored shales, such as red or green of various shades, are the exception in oil regions. Limestones. Limestones are essentially calcium carbonate. They may have various colors, but dull drab colors are the most characteristic in oil fields. Limestones tend to occur in beds thicker and 'considerably harder than the layers of shale. They can be recognized by the fact that a fragment dropped in a glass containing a strong mineral acid will effervesce vigorously. Occasionally it may be necessary to heat the acid in order to get the effervescence. Transitional Rocks. The sedimentary rocks do not commonly occur in pure layers. Thus, sandstones are very frequently mixed with a small amount of clay, while shales frequently contain a 38 POPULAR OIL GEOLOGY. small amount of disseminated sand. The same is true of limestone. For these reasons we speak of shaly sand- stone, calcareous sandstones, shaly limestones, sandy shales, and calcareous shales. All of these terms are self-explana- tory in meaning. The relationship is shown graphically on the accompanying triangular diagram. Sandstone / \ Calcareous Sandstone Shaly Sandstone / \ Sandy Limestone Sandy Shale / \ Limestone — Shaly Limestone — Calcareous Shale — Shale Formation. Sedimentary rocks may consist of a collection of pure sandstones, pure shales, or pure limestones, but more frequently they consist of several of these rocks in more or less rapidly alternating layers. Any collection of such strata whicli may be conveniently considered together is known as a "formation". In order to distinguish forma- tions, it is customary to apply the name of a town, river, mountain or other geographic locality tOi it. Thus we have a Denver formation, a Big Horn formation, a ]^iagara for- mation, and many others. Stratification. The sedimentary rocks occur in more or less well- defined and parallel layers or beds. These were originally horizontal. Each individual layer is spoken of as a stratum, and the sedimentary rocks are said to be strati- tied. Strata may be, massive layers as much as twenty feet in thickness, or they may be thin and platy like sheets of paper. In the latter case the rocks are said to be lami- nated. Cross Bedding. Occasionally the well-defined, massive beds of rocks are made up of many smaller inclined layers. The incli- nation of these may be more or less constant, which is true of those sediments that are deposited by strong currents of water. In other rocks these inclined layers may be very POPULAR OIL GEOLOGY. 39 (•(•(•('iiti'ii' and iiTegiilar in direction, suggesting the deposi- tion In- tlif shifting winds. Any inclined lamination of this sort is known as cross-bedding. It is most character- istic (if sandstunos. Variations in Rocks. All i-dfks slinw more or less tendency to vary in their characteristics. This is cs|ieeially true of their thickness. Changes in cumpcisition are also cfiniinnn. One rock may gnido intd another when traced over a large area. The pure limestone layers deposited in the quiet and deeper parts of the oceans today, cliange into shaly limestones and eventually into shale as we approach the eccan shore. Erosion Forms. The configuration of the earth's surface is subject to I'ontinual eliange, so that the hill of today may become the valley of the future. 'I'he falling rains and the driving winds tear down the earth's surfaee at one point and build it u]) in another. This ju-oeess is known as erosion. No one has cx|>rcsscd the importance of this process in words finer than the following: "The hills are shadows, and they flee From form to form, and uotliing stands; They melt like mists, the solid lamls. Like cloTids they shape themselves and go." i^aturally erosion is most active on the softer rocks, and on these the valleys are usually located. The harder rocks give us the elevations. The differences in hardness of the individual layers of a rock are clearly shown in any exposure. The harder layers project as ribs or knobs; the softer layers arc -worn away and leave pits, cavities, and irregular depressions. To])ogra])liy depends to a great extent on the attitude of the underlying rocks. In regions of horizontal rock, the harder portions jn-ojcct above the surrounding country :is flat-topped elevations of small or large surface area, known resjieetively as "buttes" and "mesas". In regions of inclined rocks, llie hai'der layers form long narrow ridges which we speak of as "hog backs". V. Stratigrapkic Geology. The part of geological science that deals with the order of succession of rock layers, and attempts to deter- mine their relative ages, is known as Stratigraphio Geol- ogy. In attempting to compare or "correlate" rocks one of three methods can be followed : Tracing Outcrops. Occasioually it happens that a particular bed of rock, such as a limestone, yields a more or less continuous expo- sure or "outcrop" on the earth's surface, which can be fol- lowed for a considerable distance, and which will hence serve as a basis for comparison. This method is, of course, subject to limitations. The time required to trace a forma- tion from a known field to the one in question may be so great as to make its cost prohibitive. There is also the probability that the outcrops may be covered for a consid- erable area. This is generally the case. Comparing Lithological Characteristics. A known formation may be characterized by certain physical properties, such as its color, its hardness, its characteristic layering or bedding, and its composition. A similar formation in a different locality may represent the same layer. This is frequently assumed, but is not necessarily true, because experience has shown that no matter how peculiar and unusual certain characteristics may appear to be, they may recur any number of times. The comparison of successive layers of rocks, of their char- acteristics and thicknesses is a more valuable method of correlation. An illustration will make this clear. In a known field we find a conglomerate three hundred feet thick succeeded by eight hundred feet of red sandstone, which in turn is followed by eleven hundred fifty feet of alternating red and green shales. Some distance away we find a succession of rocks similar in characteristics and thickness. Therefore we may argue with some safety 40 POPULAR OIL GEOLOGY. 41 that these two groups are probably equivalent in age. This method, while capable of more general application than the first, is also subject to limitations. The liability of change, both in the thicknesses and characteristics of the rock layers, must be considered. In the case of widely separated fields, the individual rock layers may have changed so much as to make this method of correlation infeasible. Use of Fossils. About one hundred years ago the British civil engi- neer, William Smith, discovered the fact that each layer of rock carries fossils which are characteristic, and that these fossils can be used to prove that widely separated rocks are of the same geological age. This discovery en- abled us to make the geological time table, especially after the doctrine of evolution had been worked out in detail. Evolution. The theory of evolution teaches us that the various types of animals and plants have developed by descent from pre-existing types. In general, progress has been from the simpler towards the more highly organized and complex types. Indications are that all animals and plants are the descendants of a very few simple organisms not unlike the simpler protozoans. The various living types of animals and plants do not form a series showing a complete grada- tion from the most simple to the most complex. Instead, they represent a genealogical tree, the branches of which exhibit very different degrees of divergence 'from the parent stock. Indeed, many of these branches are now known only by their fossil remains. Close resemblance among animal groups, such, for instance, as that between man and the anthropoid ape, does not mean descent of one from the other, but indicates a common ancestral stock. Geology has proven the fact that every species of ani- mal and plant lives only for a limited time on earth, then it dies out, and once extinct never returns. If we arrange the sedimentary rocks in a column with the oldest at the 42 POPULAR OIL GEOLOGY. bottom and the youngest on top, similar to the chronolog- ical table given later, we will find that each species of animal or plant has a certain vertical range which repre- sents its period of existence on earth. The vertical range of species is not the same in all parts of the earth. A particular animal has its origin in some definite locality and spreads laterally from there over the surface of the earth and then dies out. It does not necessarily survive last in the area of origin. 5 A IV A > A 4 - / ^... TV >K 3 E J[>. ' h A Space DIsfrfbuT/on — *• Figure 8. Diagram to sliow space and time distribution of a fossil. The accompanying diagram illustrates this fact graph- ically. The horizontal line represents distance on the earth's surface; the vertical line represents time; 1, 2, 3, 4, etc., represent the sedimentary rocks deposited in order. A is the point of origin of a particular animal which spreads laterally and with different velocities to the points E and D, and eventually disappears at the point 0. The shaded area, therefore, gives us both the time distribution and the space distribution of this species on the earth. POPULAR OIL GEOLOOY. 43 If we examine the rocks deposited at the locality A, E, or C, we will find this species characterizing rocks of slightly different iii;f' because of differences in the time of appearance and of disappearance of this species. To make a fossil especially useful for correlation it should have a small vertical range, that moans short life on earth; and in addition it must he easily and rapidly distributed over a large area. Ordinarily we use not a single fossil, but a whole collection of fossils as a basis of comparison. The group of animal fossils characterizing a formation is known as a "faunn"; the group of plant fossils, as a "flora". Preservation of Animal Remains. Fossils are the impression or remains of animals and plants entombed in the rocks by natural causes. Pres- ervation depends on the character of the organism. Only those with bony structures are capable of preservation. It will also be evident that the home of the animal has a great effect on liability of preservation. Water, and espe- cially marine animals, are far more likely to leave a fossil than land animals. The fleshy portion is never preserved. The only exception to this rule are elephants that have been found frozen in the arctic gravels in northern Siberia, in which ease the preservation of the flesh was due to excessive cold. Under ordinary conditions only the bones and the shells can fonn fossils. Occasionally bones or shells are preserved in their original condition. More fre- quently, however, they have been replaced bv some mineral matter. This simply means that the bone has gradually gone into solution and that simultaneously for each parti- cle of bone dissolved, a particle of mineral matter has been deposited. There occur quite commonly in the rocks eccentric sliaped bodies which are the result of water circulation and the o o d s o" o o o o o 0) 10 § d X c c c 5: 3 SO it c I. 1 c E 2 w i u S u 2 < a c 5 o ■a o 5 <0 o c o c a c (0 a « c o d c «!( c: o c .2 '2 5 -J § •> «cS c .2 c a: i <<3 1 E a (0 C 1 E 1 V I. The Arrangement and Structures of R.ocks. Structural p'lilnfiv deals with the arrangement and attitude of rocks in the Earth's surface. From the stand- point fif tlie oil gooloirist it is the most important branch of geological science. We have already seen that the sedimentary rocks at the time of formation are deposited in parallel layers or strata that are more or less horizontal. We may find them, liowever, standing on edge and inclined in all possible directions as n result of some disturbance since the time of their deposition. Dip and Strike. The attitude or jiosition of a stratum is a geological feature of prime importance and one that must be recorded. Figure 10. Dip and Strike. This is done by observing the dip and strike. The dip is the inclination of the bed to a horizontal plane. The strike is the bearing of tlic line of intersection of a hori- zontal plane and the plane of the stratum. The direc- tions of dip and strike are at right angles to each other. The strike is always ex])rossed by compass directions, such as North 40 West (X. 40' W.), or South 12=' East (S. 12° E.). The dip angle varies of necessity from 0° for a horizontal bed to 90° for a vertical one. Dip and -Irike are frequently rceorilod on maps bv a symbol. Thus, a straiglit line is drawn in the correct direction of the 51 52 POPtTLAE OIL GEOLOGY. strike and at right angles a shorter line is drawn in the direction of dip. The direction of the strike line indi- cates the true bearing of the strike. The dip line indi- cates the bearing of the dip but not its amount, conse- quently it is customary to mark down the value of the dip angle on the symbol. Outcrops. In order to work out the structure of rocks and to determine dips and strikes, it is necessary to locate and study outcrops ; that is, exposures of bed rock at the earth's surface. When the surface is horizontal, the outcrop of the stratum gives the direction of strike. This is not true, however, in the case of inclined layers of rock that cross rugged country with high hills and deep valleys. Here the bearing of the outcrop and the strike of a stratum may diverge widely, because the outcrop deviates from a straight line when crossing points of- different elevation. Thus, if a bed dips upstream, the outcrop travels upstream when crossing a valley ; if the bed dips downstream, the outcrop travels downstream. The amount of this deviation or travel is a fimction of the angle dip and of the depth of the valley. In many cases this enables us to calculate the dip and strike when no direct observation is feasible. Thus, the flatter the angle of dip the greater the travel of outcrop up or down stream ; the steeper the angle, the less the travel. Vertical strata show no travel. Folds. Frequently we find the outcrops of certain beds re- peated in such a way as to suggest that strata of rocks in the earth's crust have been folded in nature much like we fold sheets of paper between our fingers. Such folding is a common characteristic of oil fields. Three kinds of folds may be recognized: Anticlines, Synclines, and llonoclines (or homoclines). POPULAR OIL GEOLOGY. 53 Figure 11. Various types of Folds. 1. Symmetric Anticline. 2. Asymmetric Anticline. 3. Overturned Anticline. 4. Symmet- ric Syncline. 5. Asymmetric Syncline. 6. Overturned Syncline. 54- POPULAR OIL GEOLOGY. The anticline is an upfold in the strata or an arch. The Syneline is a downfold or a trough. The Monocline is a stepfold, or a flexure in a single direction only. The term homocline has also been applied to a number of for- mations that dip in one direction only. Degree of Folding. Folding exhibits various degrees of intensity. All gradations from very gentle rock vpaves to intricately twisted and complex crumples are shown. Simple and Figure 12. Monocline. gentle folding is most characteristic of oil regions. Com- plex, intricate folding is unfavorable in general ta oil ac- cumulation. Anticlines and synclines are usually com- bined in a series of parallel folds of wavelike character, with the anticlines at the crests and the synclines at the troughs. Both occur in a variety of forms. They may be low and broad, or acute and sharply compressed. They may be horizontal, vertical, or inclined in position. The amount of folding is roughly measured by the difference in elevation of the same layers of rock between the lowest part in the syneline and the highest part in the anticline. This varies from a few feet to several miles. In Wyoming oil fields this is usually large, and varies from several hundred feet to one mile. In Oldahoma and Illinois, this is usually less than two hundred feet. POPULAR OIL GEOLOGY. 55 Nomenclature of Folds. Tlic sides of the folds are known as liml)-*. The axis is the ill reft ion of elongation. The anticlinal axi< is the liiiilicst part of the anticline, or its crost. TJie axis of a syufline is the bottom of the trough. Fulds are symmetri- cal or unsymmetrical, depending on whether or not the dip of the limbs from the axis is equal in opposite direc- tions. Folds are horizontal when the axis is horizontal. Folds with an inclined axis are plunging or pitching folds. \'arious folds are indicated l)y the dip and strike symbols in the accompanying figures. \ / \ \ \ \ \ \ \ \ \ / \ 0astn / / / SyrK/ifte ^/t/fiqin^ 'Sy/tc/*'ffC X X \ x^ Oomm \ \ \ P/unytng Ant/c//fre Figure 13. Various structures as represented by tlieir dip and strike symbols. Composite Folds. Two types of folds of extreme importance to an oil man are dome folds and basin folds. Both may be con- ceived of as composite folds, consisting of two folds cross- ing at right angles. In domes, or quaquaversal folds, the rocks have the attitude of an inverted bowl and dip away 56 POPULAR OIL GEOLOGY. in all directions from the center. In Basin, or centro- clinal folds, rocks are arranged in the shape of a natural basin and hence dip into the center of the fold. Domes and Basins also have axes corresponding to the axes of anticlines and synclines. The axis of a dome marks the highest part and the line of elongation of the fold. The highest point on the axis is the apex. Faults. In many regions we find that the rocks have been fractured and broken on an extensive scale, and that the broken parts have been displaced with respect to each other. Such displacement on opposite sides of a fracture or fis- sure, is a fault. The fracture is the fault plane. This is usually inclined. The two sides of the fault are known as the footwall and hanging wall, respectively ; see figure 14. According to the character of the motion we recognize two great classes of faults : normal faults and thrust faults. Figure 14. Normal Fault. Normal Faults. These usually have steep dipping fault planes and are produced by the tension or stretching of rocks. In these, the hanging wall moves down with respect to the footwall. POPULAK OIL GEOLOGY. 57 Thrust Faults. The majority of thrust faults have flat, dipping fault planes. They are most common in regions of intricate and fc implex folding. In these faults the hanging wall moves up ovrr the fnotwall. They are produced by lateral press- ure and the crowding of rocks over each other. Figure 15. Thrust Fault. Displacement. Tlic actual amount of motion in the fault plane is the displacement. This may vary from a fraction of an inch tn sevonil miles. Normal faults are most common in oil fields. Th(>so usually have displacements of a few hundred feet or less. Complex faulting on a large scale is unfavor- able to oil accumulation. Figure 16. Apparent change in character of roclcs due to faulting shown by Well No. 2. (U. S. Geol. Sur.) 58 POPULAR OIL GEOLOGY. POPULAR OIL GEOLOGY. 59 Unconformities. Tlic sedimentary rocks are deposited in a regular and systematic order. Each stratum represents a definite time interval ; all collectively represent a continuous space of time. The regular succession of rocks may be broken or internipted. For example, after the deposition of marine strata there may be an emergence of the continent from the- ocean, which exposes the recently formed strata to ero- sion. These may be folded and faulted and eroded into hills and valleys. Subsequently the continent may rgain be submerged under the ocean and new deposits may be laid down on the dissected surface of the older series. The younger beds, therefore, do not conform to tlie older rocks below. A surface of contact of this nature is an Uncon- formity. The Sedimentary Rocks record Earth history. The rocks above and below the unconformity record periods of time perhaps less extensive than the duration represented by the unconformity. This marks a lost time interval sim- ilar to a chapter torn out of a novel. Unconformities may be clearly shown by differences in attitude of rocks indi- cating that the older series of rocks were tilted and folded and eroded preceding the deposition of the younger series. They are quite important and their influciice must bo care- fully considered in certain oil fields. VII. Reservoirs of Oil and Gas. Any rock that is capable of containing oil and gas in commercial quantities is known as a "reservoir". The most common types of reservoir rocks are: First, sand- stones; second, limestones; and third, shales. These v^ill be discussed briefly. Sandstones. Sandstones are the most common type of reservoir rocks. The amount of oil that any sandstone may carry is determined by the number and size of openings it con- tains, or, in other words, its porosity. This depends on the size and shape of the grains, and on the degree of cementation. The greatest amount of pore space is pos- sessed by the rock that has spherical grains of uniform size ; the least amount of pore space, by the sandstone made up of unassorted angular grains. Cement is quite important in determining porosity because it clogs up the interstices between the grains to a greater or less degree. A well- cemented sandstone is hard; a loosely cemented one, soft and friable, that is, it may be crumbled in the hands. Hard, well-cemented sandstones form the reservoir rocks in the Appalachian oil fields, in Illinois, Kansas and Okla- homa. Soft, friable sandstones form the reservoirs in Wyo- ming, Colorado, and in northern Texas and Louisiana. The oil production from California, Russia, Galicia, Eou- mania, and Peru comes from unconsolidated, loose beds of sand. According to the amount of pore space, we speak of "close" or "tight" sands, which means those of low poros- ity, and of "open" sands, those of high porosity. The amount of pore space of any sandstone can readily be determined by saturating the dry rock completely with water and noting the amount of water absorbed. The porosity so determined is known as theoretical porosity. This varies from one-half percent in the case of quartzite, to 30 percent in the case of sand. The general average 60 POPULAR OIL GEOLOGY. 61 Figure 18. Diagram Illustrating the effect of size of grain and method of packing on porosity. 62 POPULAR OIL GEOLOGY. is 10 percent. This isi the equivalent of seven hundred seventy-six barrels of oil per acre-foot. This means that a sandstone bed one foot in thickness and extending over one acre, will contain seven hundred seventy-six barrels of oil. We must, hov?ever, carry in mind the fact that there is a difference betvpeen theoretical and practical po- rosity. While the theoretical porosity may be 10 per- cent, the practical porosity is far less, because ordi- narily only from 50 percent to 75 percent of the oil in the sand can be recovered. Thus in the Appalachian fields the practical porosity is 4.5 percent, which is equiv- alent to three hundred fifty barrels of oil per acre-foot. At Glennpool, in Oklahoma, the practical porosity is 6.5 percent, which means that five hundred thirty-five barrels of oil can be extracted for each acre-foot of sand. Extraction is favored by high porosity, by large and con- nected openings, and by low viscosity of the oil. All of these factors promote ready circulation and easy flow. In the case of unconsolidated sands, even a highly viscous oil may flow readily because of the fact that it will carry the sand along with it. Thus in some of the Russian and Califomian fields, more than 50 percent of the material flowing out of the well is sand. In color oil sands vary decidedly. Usually they are darker in color than the barren sands. Asphalt oils leave yellow to brown stains on the rock and impart to it the odor of petroleum. The paraffin base oils are so light and evaporate so readily that frequently no trace is visible in the outcropping oil sands. Test for Oil in Sands. The presence of inspissated hydrocarbons in an out- cropping sand can be determined by sampling the outcrop, crushing the rock and treating a tablespoonful of the frag- ments with ether in a well-corked bottle for half an hour. Any hydrocarbons present will go in solution. If subse- quently the liquid be poured off into a white china dish, it will evaporate rapidly and leave behind a ring of oil. This will be greenish amber to pale brovsm in color in the POPULAB OIL GEOLOGY. 63 case of very high-grade paraffin base oils, or dark brown to black in color in the case of asphalt base oils. Shape of Reservoir. Certain sandstones occur in well-defined strata that are more or less constant in thickness, and that extend over very liirf;e areas. An example of such is the Dakota sandstone which is known to extend over an area of two thousand by one thousand miles. More frequently, sand- stones are lenticular in structure. They are limited in areal distribution and thin out or "pinch out" laterally. The entire sandstone bed must not be thought of as being WCUNO.I IVCLLN0.3 Figure 19. Lenticular sands and their effect on wells. (U. S. Geol. Sur.) a reservoir. There are certain portions that may be in- capable of holding either oil or water because of the fact that they are very tightly cemented, or perhaps made up of excessively fine grains. The resei-voir is confined to the porous part of the sandstone where the grains are coarser and consequently the interstitial cavities are larger, or where the cement is poorer and does not completely fill the room between the grains. The accompanying sketch map shows a small area vmderlain by oil sands. The reser- voirs are indicated by shading. It will be noticed that the oil pools are restricted laterally, not by the structure nor by the extent of the sandstone, but by the porous layers capable of acting as resei-voirs. POPULAB OIL GEOLOGY. Figure 20. Lenticular layers in oil sands shown by shading. Cross hatching shows oil, dotting gas, brolien lines water. Limestones. The limestones that we meet with in oil fields repre- sent the fragments of the shells of animals and the skele- tons of corals, which have been compacted into rock. Fos- sils are plainly visible in many limestones. In many others they are very indistinct and may be completely de- stroyed. Limestones are essentially calcium carbonate. Wlien pure they are ordinarily unfavorable as oil reser- voirs. Certain limestones, known as dolomitic limestones, or dolomites, carry varying amounts of magnesium. Such contain oil or gas in a number of prominent fields. While there are differences of opinion as to the origin of the POPULAK OIL GEOLOGY. 65 dolomites, it is generally conceded that magnesium carbon- ate, which is brought into the limestone by circulating solutit>ns, takes the place of a certain number of calcium carbonate molecules. Since the specific gravity of magne- sium carbonate is greater than that of calcium carbonate, less space is required for each magnesium carbonate mole- cule, and as a result we have a shrinkage of volume in the (iriijiiinl rock. The shrinkage is equal to 1:^.30 percent. Thus if one hundred cubic feet of limestone has one-half of its molecules of calcium carbonate replaced by magne- sium carbonate, the resulting rock will have 12.30 cubic feet of pore space. These openings serve as receptacles for oil and for gas. Doloraitic limestones form the reservoir rock of the Lima field of Ohio and Indiana, of Spindle Top and other fields in Texns, and of Jlaiileii-i-Xapthun in Persia. The oils in limestone are usually of asphalt base and are high in sulphur and in nitrogen. Pure linicsttincs are quite easily soluble. Conse- quently cin'ulating water will dissolve out caves and chan- nels. The extensive cave systems of ]\lammoth Cave in Kentucky and of Wind Cave in South Dakota are famil- iar examples. Water channels of this sort may occasionally act as reservoirs. This is true in certain of the ]\loxican fields. Oil will flow very readily in such reservoirs. Con- sequently wells of great capacity and usually short life may be expected. Shales. The older geologists emphasized the importance of rock fractures and fissures ns oil containers, and believed these to be far more important than the interstitial cavi- ties between sand grains or the shrinkage cavities in lime- stones. At the present time this idea is applied to but a few pools. For example, at Florence, Colorado, oil is foimd in open fissures and fractures in a thick bed of shale. Several other localities, such as West Salt Creek, in Wyo- ming, and a few areas in Pennsylvania, show a similar type of accumulation. Generally, however, it may be said that such occurrence is unimportant and unreliable. 66 POPULAE OIL GEOLOGY. 2SS. Z7S iss dhari «o IJJ Limm ia3- 170 Lima 170 IBS a>iai* 200- 330 Umt JJO- MO Shdte 360- •416 Sand 4(5- 430 Shmf 4J0- 340 3and S40- sso Shalt «w- >«0 Sana C«0- 400 Elttarado ahalUvi oH 5«nd. Shah «ao- 0OO Limt 600 9O0 M Lima sand B 940- 970- i for* I040 1030 IOT3 L.tm* 1075- ■ 333 3haU I 333- (400 tim* •400- 1305 Snel* iAS3-i3t* Sond 1323- 1333 Snste 1333- iTiO Lim« iTiO>iaO0 Smnd 1080- 1000 ShdM 1690-2003 LM/c Zi«0-Z9lO Limtf 23I0-Z970 3hafe Z»70-Z«3o TYPiCAL NMLLLOG Figure 21. Map of the Augusta and Eldorado pools in Kansas and typical well log. (After Hager) POPULAR OIL GEOLOGT. 67 Other Rocks. The al)Ovf! include all important reservoir rocks, al- though small quantities of both oil and gas occur occasion- ally in crystalline rocks. At the recently discovered Thrall oil field in Williamson County, Texas, the reservoir rock is a basic igneous rock known as limburgite. It owes its porosity in large part to extensive alteration by circulating underground wafer. The oil and gas it contains are de- rived fi-diii tlie surrounding ( 'rct;iec'cius sediments with which this imeous I'ock is interbedded. '&' The Enclosing Beds of Reservoirs. Reservoir rocks must be retained between rocks im- pervious to the circulation of oil, as, without these, we could expect no commercial accumulation. The most com- mon type of enclosing beds are water-wet, fine-grained rocks, such as clays and shales. Occasionally, the enclos- ing rocks are similar to the resen'dirs, but eitlier so tightly cemented or so exeessivdy fine-i;viiined ;is U> make the movement of oil thr(iiii;li tlicin imiiossilile. VIII. Tke Laws of Migration and Accumu- lation of Oil and Gas. In the preceding discussion we concluded that oil and gas are formed by the distillation of plant and animal re- mains which are buried in the rocks by natural causes at the time of their deposition. Of all sediments, muds are most prolific in organic remains. It seems highly probable, therefore, that by far the greater part of oil and gas was originally formed in shales. Since neither oil nor gas occur in any great quantity in this rock, we are driven to the conclusion that they have migrated from shale and have been concentrated in rocks more suitable as reservoirs. Causes of Migration. A number of different causes have probably been act- ive in forcing such migration, chief among which we may mention the following: 1. Differences in specific gravity of gas, oil, and water. 2. Head of ground water. 3. Gas pressure. 4. Eock pressure. 5. Earth movement. 6. Heat gradient. 7. Capillary attraction. Differences in Specific Gravities, It is a well-known fact that gas is lighter than oil, and oil lighter than water. Oil and water are not miscible. Oil floats, therefore,. on the surface of the water. Conse- quently, wherever oil and water are mixed in rocks under the earth's surface oil should be on the top, and wherever water moves through rocks, oil must be driven ahead of it. Many phenomena tend to show that ground water is seldom stagnant, but instead is subject to gentle and continuous circulation, and for this reason, many geologists see in the 68 POPULAR OIL GEOLOGY. 69 differences of the specific gravities of oil and water the most powerful cause of oil migration. Head of Ground Water. The water in the rocks of the earth's crust is known as ground water, or undergrouml water. Tliis water is under pressures whicii is known tlieoretic;illv as "head". The head is the factor determining; the heifjlil to which water will rise. "Head", therefore, causes water to flow, and for the reasons already mentioned, oil and gas are driven ahead of the M'atcr thrmifili the rocks. In many fields the head of the ground water has been determined and for a large number of cases proved to be equivalent to the pressure on the oil and gas as determined in the wells. Thus for many of the Ohio fields the pressure on the oil is equivalent to the head of water standing at the level of Lake Erie. Gas Pressure. The gas associated with oil is frequently \inder very great pressure. Maxima of fifteen hundred pounds to the square inch liavc been recorded. This pressure is of neces- sity exerted in all directions and may to some extent force oil to move through rocks. Gns pressure is of great im- portance in certain oil fields because it may lie sufficiently great to force the oil through the well up to the surface of the earth and so produce flowing wells or gushers. It is probably not a very important cause of oil migi-ation. Gas migrates in all directions far more easily than oil. Gas fields, therefore, are of larger extent than oil fields, and may be entirely distinct from them. Rock Pressure. Rocks underneath the earth's surface are under pres- sure equivalent to the weight of the column of rocks above them. With increasing depth this pressure may be so great that no openings can exist, and that the rocks will flow like wax. Such pressure is hydrostatic, that is, sim- ilar to pressure under water, equal in all directions. Kocks under such pressure are said to be in the zone of flowage. 70 POPULAR OIL GEOLOGY. As will be evident, the pressure necessary to bring about this condition will vary with the rocks. Kocks of high crushing strength, such as well-indurated sandstones, re- quire a pressure equivalent to a burial of several miles; clay shales on the other hand, are in a condition of flowage after burial of three hundred feet and perhaps less. The effect of rocks whose pores and openings are saturated with oil or water will be similar to that of a sponge saturated with water and subject to pressure. The liquid and lighter material will be gradually squeezed out and forced towards the surface. Rock pressure is undoubtedly a very potent cause of oil migration, especially in rocks deeply buried. Below four thousand feet it is probably the most important cause of movement. Earth Movements. Earth movements, such as folding and faulting and tidal deformations, set up stresses and strains in the in- terior of the earth which have some stimulating effect on oil migration. Their importance is probably very slight. Heat Gradient. As we descend from the earth's surface, we find that the temperature increases at a more or less regular rate of 1° C for every fifty to one hundred feet. This regu- larly increasing temperature may have a slight stimulating effect on circulation. The general tendency will be to drive the liquids upward. Its importance is probably very slight, because of the great depth required for an effective temperature increase. Thus a burial of one mile is only equivalent to a temperatuvp increase of 50° to 100° C. Capillary Attraction. The tendency of liquids to ascend minute openings and pores, such as those in sponges, is a result of capillary attraction. Any opening of tube shape and less than one- half millimeter (one-fiftieth of an inch) in diameter is a capillary opening. Liquids will tend to rise in such tubes against the effects of gravity. The height of such rise will depend upon the nature of the liquid, the size of the tube. POPULAR OIL GEOLOGY. 71 and tlic material of the tube. The effective pressure that fnrcos liquids to ascend such tubes, is capillary pressure. This is a function of the surface tension of the liquid and the attraction between the liquid and the tube. The greater the surface tension the greater the capillary pres- sure, consequently the greater the tendency to enter micro- scii|iic. pores. Water has a surface tension three times that of crude oil. Water therefore, exerts a capillary pressure three times as great as that of crude oil. Figure 22. Rise of a Water-Oil emulsion between plates of glass as a result of capillary attraction. Cross-hatched area is oil. Note that on separating, the water has occupied the space of smallest size. Considering the fact that a mixture of oil and M-ater is disseminated through the rocks of the earth's crust, it will be evident that the differences in surface tension will cause a selective segregation of oil and water. The water, be- cause of its superior surface tension, occupies the pores of smaller diameter; the oil is driven into the opening of larger size. Capillary pressure decreases with rise in tem- jierniure. Because of the increase in temperature due to lie;it gfiidient, it is virtually negligible in rocks at a depth I if .several miles. 12 POPULAB OIL GEOLOGY. Conclusions. All the factors discussed separately, probably played a part in causing oil migration. To some extent, at least, tbeir effects can be differentiated. The original sedi- ments, which consist in greater part of muds with minor layers of sand or perhaps porous limestone, must suffer considerable compacting at the time of their consolidation into rock. The muds especially are subject to a consider- able shrinkage of volume, which is mainly the result of rock pressure. The sands and limestones offer greater re- sistance to pressure and cannot be compacted to the same degree. Their pores will remain open and will serve as reservoirs for the liquid materials squeezed from the clays and mud. Capillary pressure also plays a role and prob- ably the most important one, in affecting a primary con- centration of oil and gas in the reservoir rocks. Thus in the progress of time, the oil and gas contained in the shales will be driven out by water because of its greater capillary pressure, and will be forced into the rook with larger pores — the reservoir. Rock pressure and capillary pressure are chiefly im- portant in collecting oil and gas in reservoir rocks. They will be disseminated through the entire formation, and only under very exceptional conditions can they be concen- trated into commercial pools by rock pressure and capil- lary pressure alone. Oil pools in fissured shale may owe their existence mainly to such concentration. In the majority of cases the concentration of oil and gas into commercial pools is the result of the differences in the specific gravities of oil, gas and water, and of the movements of the underground water. Oil and gas rise to the top of the water, and wherever currents exist move ahead of the water surface through the reservoir rocks. >A concentration of large quantities of oil and gas may take place where suitable structural conditions exist. The term "trap" is frequently apjjlied to such a condition, and is quite appropriate. POPULAR OIL GEOLOGY. 73 Gas pressure and water pressure due to head are the most important causes of flowing wells, with one or the other dominant, depending upon local conditions. Laws of Oil Accumulation. The laws of oil accumulation, although relatively sim- ple, were not clearly formulated until 1885. In that year, I. 0. White published what is known as the "anticlinal theory". This is probably the most important single con- cept of oil geology which in more or less modified form, governs oil accumulation in virtually all oil fields. In oil fields we do not find the sedimentary rocks flat and undis- turbed as they were originally deposited, but we find them folded and wrinkled much like the quilt on our bed after a night's sleep. The upfolds or arches are anticlines; the downfolds or troughs are synclines. Experience has shown that the higher parts of the folds, that is, the anti- clines, are more likely to carry oil. This is explained as follows : The sandstones or limestones which act as oil and gas reservoirs ai'c, in most cases, saturated with water. They are overlain and underlain by shale or some other rock which forms a more or less impervious cover. Oil and water, even if vigorously stin-ed up and shaken in a bottle will not mix, but will separate in two layers according to their weight — the oil on top, the water below. Similarly in the oil sand such a-separation will take place. If the sand be completely saturated or filled M'ith water, the oil will rise to the highest part of the reservoir — which is the very top or crest of the anticline. If the sands are only partially saturated, the oil will accumulate on top of the water level along the sides of the folds. If the sands are dry, the oil of necessity will be found in the bottom of the troughs — or, to use the geologic term, in the syncline. In by far the great majority of cases, the oil sands are com- pletely saturated, and the oil accumulates therefore in the crests of the anticlines. These are the conditions met with in the most fields of Wyoming, California, and the Appa- 74 POPULAE OIL GEOLOGY. lachians. Whether or not a sand is saturated can only be determined by drilling. In many fields noticeable quantities of gas accompany the oil. This, being the lightest constituent present, rises to the top of the oil. The occurrence of gas wells, oil wells, and water wells on the same structure is explained by the fact that the oil sands are penetrated at different eleva- tions ; the gas well at the highest ; the oil well at an inter- mediate; and the water well at a lower elevation. The accompanying figure makes this clear. Figure 23. Section illustrating the occurrence of a gas well (A) ; an oil well (B), and a water well (C) on the same anticline. There are a number of other structural arrangements of rock that afford suitable traps for oil accumulation. These will be discussed in some detail in the following chapter. No matter what the structure may be, we must have a porous rock, usually a sandstone, that is capable of act- ing as a reservoir and that is enclosed in relatively imper- vious rock, usually shale. The arrangement of rocks must be such that there exists an opportunity for the accumula- tion of commercial quantities of oil and gas. The most important single factor in the locating of an oil well isj therefore, the geologic structure. The chief value of any geologist is his ability to determine the structure from the distribution and arrangement of the rocks at the surface, and to locate the favorable areas for testing. It may be POPULAK OIL GEOLOGY. 75 well to emphasize the fact that a perfect geologic structure is not necessarily an assurance of a producing well. The presence of an oil-pool can only be determined by an actual test. The correct application of geologic principles does not ensure success; it minimizes risks. Under the most favorable geological conditions, drilling in untested and new areas has only about one chance out of three for suc- cess. On the other hand, a disregard of geological condi- tions in drilling a well is practically an assurance of fail- ure. IX. Maps and Tkeir Uses. Nearly every report on an oil field, whether a govern- ment report or one made for private interests, includes a map of some sort. This is not surprising because a great amount of information can be shown on a map in a con- densed form and in such a way as to summarize clearly the importance features of the region. Three kinds of maps are most frequently used. These are topographic maps, geologic maps, and structural maps. Topographic Maps. Topographic maps are intended to show the configura- tion or relief of the earth's surface, the distribution of the hills, valleys, mountains, streams, roads and similar fea- tures. The United States Geological Survey has com- pleted over twenty-five hundred topographic maps scattered through every state of the union, each of which covers an area of from about two hundred to about three thousand square miles. These maps show the earth's relief by means of contour lines, which are lines drawn through points of equal elevation at a definitely stated interval, known as the contour interval, above sea level. On the .government maps these contour lines are drawn in brown. Each fifth line is drawn heavy and has inserted at frequent intervals its elevation above sea level. The contour interval depends on the ruggedness of the country. In the western states it is usually fifty feet. Water is always drawn in blue, while the work of man — culture, as it is called — such as roads, buildings, railroads, and land divisions, is indicated in black. The spacing of contours indicate the slope. A long, gentle slope has few contours widely spaced ; a steep slope has contours closely crowded. The accompanying figure shows an ideal sketch of a landscape and the corre- sponding contour map. The relief features of the earth's surface are deter- mined by the geological structure. Much useful informa- 76 POPULAE OIL GEOLOGY. 77 tioii ciin therefore be obtained from a careful study of the t(>])(p.s;niphy or the topographic map. Crvstalline rocks ai-e very resistant to erosion. They usually form rough, irngular, and steep slopes. The topography is character- izeil by i;ciicr;il ruggedness. .Soiliinciitary rocks give a ninro varied topogi-aphy. The well cemented sandstones and conglomerates and the limestonos usually form the Figure 24. Ideal landscape and its contour map. (U. S. Geol. Sur.) steeper slopes and the elevations ; shales form the gentle slopes and tlic valleys. Horizontal sedimentary rocks pro- duce a decided similarity in surface features over the whole area, so much so that almost any square mile of the area of tlie map may be substituted for any other with- out produeing any marked change. Occasional buttes and mesas may remain as elevations. The streams have a char- acteristic, treelike or dendritic shape. Inclined sedimen- 78 POPULAR OIL GEOLOGY. tary rocks produce a topography characterized by a linear arrangement parallel to the strike of the rocks. The hard layers form more or less parallel hogbacks, the softer lay- ers the valleys between. The main streams usually cross hard and soft layers alike. The tributaries are confined to the softer layers and are arranged in a roughly parallel manner. Geologic Maps. The topographic map is frequently used as a base map upon which is recorded by means of suitable symbols or colors, the distribution of the various geological formations at the earth's surface. The structure of the rocks deter- mines this distribution ; conversely, therefore, the struc- ture may be determined from the distribution of forma- tions as shown by the map. Thus in dome folds we find the older rooks in the center surrounded by progressively younger rocks as we go outward. In a basin we find the younger rocks in the center surrounded by rocks progress- ively older. Columnar Section. Every geological report includes a columnar section intended for the purpose of interpreting the map. This is an aiTangement of all the formations in a vertical col- umn according to age, with the oldest at the bottom. The thickness of each rock member and its lithologic charac- ter are also indicated. Thus limestones are shown by masonry pattern ; sandstones, by dots ; and shales by closely crowded parallel lines. Intermediate rock types, such as calcareous shales, are shown by a combination of two such patterns. Certain beds of rock are located with great ac- curacy in the columnar section because they can be readily recognized, and hence are of value as "index beds" or "key horizons". Structure Sections. Most maps are accompanied by a structure section. This is a drawing of a vertical section through the earth's POPULAR OIL GEOLOGY. 79 Figure 25. Map and section of Ideal dome. 80 POPULAE OIL GEOLOGY. surface and shows the various rock formations in their true attitude. A structure section is usually drawn to scale, consequently we can determine by a direct measurement the depth down to any bed of rook for any point on the line of the section. Structure Map. Most of the maps of oil and gas fields are structure maps. These show the attitude or structure of a particular bed of rock, such as an oil sand, by means of structure contours. These are lines similar to the contour lines used on a topographic map. They are not, however, drawn through points on the earth's surface — but instead, through points of equal elevation on top of a certain bed of rock. The contours indicate by their arrangement the structure of the rock layer and its elevation above sea level for all points. Maps of this sort are very usefiil as they show at a glance the attitude of the rocks over the entire area cov- ered, and at the same time enable us to determine the depth from the earth's surface to any rook layer whose posi- tion is given in the columnar section. The structure con- tours are drawn from the surface exposures of the rock and their observed dips and strikes, which enable us to calcu- late the depth to the rock in question. A structure map can be drawn with very great accuracy in the developed fields because reliable information can be obtained by a study of the well-logs and records. Isochore Lines. In certain oil fields the beds of rock exposed at the earth's surface are not absolutely parallel to the oil sand. As a result the normal distance between a certain layer of surface rock and the oil sand gradually diminishes in one direction. The rate of approach for two layers of rock is subject to much variation. It may be a few feet per mile or several hundred. This feature must be considered in interpreting the structure of any field, because the struc- ture of the oil sand may not coincide with the structure of the surface rock. Hence, the area which appears to be POPULAK OIL OEOLOGV. 81 Mluitiitian bI «n iriliclin*! gu fi«ld in Panniylfanli in which Hiiril und* in productn* A thowi It) ■i>d dip ef lurflc* >t'il*. v'lth.poii- i'o"i«(iil -tlU. Bikow) Uj tniiif sf • ihttlow und, wUh poiition* of wall* drilltd 1o It, C ii ■ conmgine* mip uMd in mIcuImioji ito l«j of tlit JMp unrf far . D,iK»«i t*j~*nd dip d( ■ d(«p Mnd. with poulloni sf wilU drIIUd Is iL Figure 26. The application of convergence maps. (After Clapp) 82 POPULAR OIL GEOLOGY. favorable as judged from surface exposures may in reality be unfavorable in the productive horizon. For this reason it is necessary to determine the rate of approach of a cer- tain keybed at the surface and the oil sand, and to con- struct a "convergence sheet", that is, a map -which shows for all points the actual vertical distance between the key- bed and the oil sand. This is done by means of isochore lines — that is, lines of equal distance which are drawn a definite interval apart. The convergence sheet — or iso- chore map— r<5an then be superimposed upon the structure map of the key horizon and from the two, the structure map of the oil sand can be drawn. X. Oil Structures. Structure. Any arrangement of the rocks of such a nature as to form a trap suitable for the accumulation of commercial quantities of oil, is known as a "structure". Such may occur in a great variety of forms and in considerable com- plexity. Classification of Oil Fields on Basis of Structure. Ivxpiricufp has shown that the various oil fields have corlain geological structures that are characteristic and dis- tinc'li\f, and that vary decidedly from field to field. The t'lilliiwini;' classification of American oil fields is based on structure: I. Fields with Folded Structure. The Appalachian field. Illinois. OklahoMiii-KiUisas. California. Wyoming. Colorado. If. Fields with Monoclinal Dip (Homoclines). Ohio-Indiana. California (minor importance). Wyoming (minor importance). III. Fields on Domes. Wyoming. Ohio. Louisiana-Texas. Mexico. IV. Fields on Faults. California (of minor importance). Wyoming (of minor importance). V. Fields on Unconformities. California Wyoming (of very minor importance). Oklahoma Quebec and Ontario. JN"orthern "Rew York. 83 84 POPULAB OIL GEOLOGY. POPULAR OIL GEOLOGY. 85 m or WILO lUU U lUU JUU MO Figure 28. The oil fields of the United States. (After Johnson & Huntleigh) Fields with Folded Structure. By far the greater part of the oil fields of the world are in regions characterized by folding. This is true of virtually all important foreign fields, such as those of Eus- .«ia, Gnlicia, Roumanin, India, Persia, Peru, and the Dutch 86 POPULAR OIL GEOLOGY. East Indies. The folds may consist of closely crowded and rapidly alternating anticlines and synclines, or of large isolated anticlines standing some distance away from the general area of folding. The degree of folding differs very decidedly in the different fields. Thus, in the Eastern fields and in Oklahoma and Kansas the folds are very gentle and show dips of a few degrees only. In some cases the dips of the beds are so flat that they can only be deter- EXPLANATIONS: Structure-Contour Lines, Showing Lay" of Gu Sand*. • Oil Wall: -J^ Gaj Well; -^ Dry Hole; our HOu. ^e*a WELL. • on WEU, K W K 1 CC^E Ml aiu Figure 34. Surface struc- ture on same area as in Fig- ure 33. (After Clapp) Structural Terrace. A change in the rate of the dip sufiicient to cause a noticeable flattening of the rocks produces a structurr, which is known as a "structural terrace" or as an "arrested anticline".' The change in dip may be sufficient to retain POPULAE OIL GEOLOGY. 91 oil and gas in commercial quantities. Terraces of this na- ture have been quite productive in the Ohio fields and else- where, but have not been tested out in Wyoming with the possible exception of the Big Muddy field, which may be considered to be a big terrace. In many cases an actual trap for oil and gas exists, in others, the oil is escaping on the updip side of the terrace. In the latter case there may be an accumulation because of the slow motion of the oil through the terrace and the relatively rapid addition of oil from the downdip side. Figure 35. Oil accumulation on a structural ravine. Ohio. (U. S. Geol. Sur.) Structural Ravines and Valleys. A change in the direction of the dip may produce a suit of triinsverse wrinkle iu the rocks which looks like a valley or ravine on the earth's surface. Folds of this sort are usually diagonal to the general slope of the rocks and die out gradually by flattening in the direction of their axes. They may entrap oil or retard its passage for a sufficiently long time to make a commercial accumulation possible. Many examples of such structures are known from the Ohio, Oklahoma and Pennsylvania fields. 92 POPULAB OIL GEOLOGY. Lenticular Structure. In the preceding pages attention was called to the fact that many sandstones possess a lenticular structure, that is, they disappear by thinning in various directions. A len- ticular sand of this nature enclosed in impervious beds and not actually outcropping would form an ideal reservoir for oil and gas. The gas sands of eastern Ohio are of this nature. Asphalt Sealed Sands. Oil-bearing sands that outcrop at the earth's surface usually give oil and gas seeps. Because of this fact they are frequently drilled down the dip in the hope of striking an oil pool. This is not justified unless there is evidence of the existence of a terrace or structural ravine. Certain heavy oils may carry so much base, especially in the form Figure 36. Accumulations in lenticular sands. of asphalt, that this may clog up all the pores in the sand in the outcrop and so form an effective seal on the remain- ing oil. Such accumulations are reported from the Island of Trinidad. They are very rare, however, and need not be expected in the light Wyoming and Colorado oils, as these do not carry enough heavy base to seal a sand. A number of outcropping oil sands have been drilled down- dip, both in Colorado and Wyoming, but with disappoint- ing results in every case. Fields on Domes. Some of the world's most productive oil fields are located on dome structures. Among the best known of POPULAR OIL GEOLOGY. 93 a '$ o si m lio a a o a m 94 POPULAR OIL GEOLOGY. Oil Structures in Wyoming. No. on Produces Formation Formation Producing Map Name at Surface or Possible Producer 1— Salt Creels Light Oil Niobrara Wall Creek 2 — Grass Creek Light Oil Niobrara Wall Creek 3— Big Muddy Light Oil Pierre Shannon and Wall Creek 4 — Elk Basin Light Oil Cody Wall Creek 6 — Lost Soldier Light Oil Niobrara Wall Creek 6 — Basin Light Oil and Gas Frontier Mowry 7 — Greybull Light Oil Frontier Mowry and Dakota 8— Pilot Butte Light Oil Cody Niobrara 9 — Byron Light Oil and Gas Cody (Niobrara) Wall Creek and Dakota 10— Little Buf- and Morrison falo Basin Gas Pierre Wall Creek 11 — Oregon Basin Gas Cody (Niobrara) Rusty Beds, Cleverly 12— Dallas Heavy Oil Chugwater Embar and Tensleep 13 — Lander Heavy Oil Chugwattr Embar and Tensleep 14 — Sage Creek Heavy Oil Chugwater Embar and Tensleep 16 — Thermopolls Heavy Oil Chugwater Embar and Tensleep 16 — Douglas Light Oil White River Cretaceous sands and Tertiary- Basal White River. 17 — Spring Valley Light Oil Aspen Aspen 18 — La Barge 19 — Vermillion Tertiary Aspen (Mowry Shale) 20 — Hawlins Various Embar ' 21 — Laramie ^^tlt tJCLL Plains Pierre Frontier 22 — Oil Mountain Sundance Embar — Tensleep 23 — Rattlesnake Mountains Various Embar — ^Tensleep 24 — Washakie . t*A AU Ll .3 25 — Newcastle Ligh'tOi'l" Benton Sandstone In Benton 26 — Moorcroft Light Oil Benton — Dakota Benton — Dakota 27 — Bonanza Light Oil Mowry Dakota 28 — Sunshine Mowry Dakota 29 — Cody or Shoshone Light Oil and Gas Frontier Mowry — Thermopolis — 30 — Shannon Heavy Paraffin Cleverly Oil Pierre Shannon 3 1 — Cottonwood Mowry Dakota 32 — Cottonwood Creek Mowry and 33— Alkali Butte lower Dakota 34 — Dry Piney 35 — Rock Springs 36 — Wheeler Pierre Wail Creek 37 — Powder River Jet. Mesaverde Shannon — ^Frontier Embar — Tensleep Embar — Tensleep Basal Paleozoic Embar — Tensleep Frontier 38— Tlsdale Sundance 39 — Kaycee Morrison 40 — Sheep Mtn. Madison 41— Shell Creek Morrison 42 — Dry Creek Cody 43 — Mercer Sundance Embar — Tensleep Frontier — Cleverly Embar — Tensleep Embar — Tensleep Madison Madison 44 — Manderson Cody 45 — Palntrock Sundance 46 — No wood Chugwater Tensleep Tensleep 47 — Ziesman 4 8 — Brokenback 49 — Sherard Oil and Gas Frontier Mowry — Cleverly POPULAR OIL GEOLOGY. Oil Structures in Wyoming — Cent. 95 No. on Map Name Produces Formation at Surface Formation Producing or Possible Producer 50— Well Area 61 — Tensleep 62 — Bud Kimball 63 — Mahogany Butte 64— Lyslte Mtn. 66— Black Mtn. 66 — Lake Creek 67 — ^Zimmerman Butte Cody Mowry Chugwater Madison Mowry Mowry Frontier Cody Thermopolls Embar Chugwater Morrison Fort Union Cody Cody Cody Cody Cody Cody Frontier Mowry Mowry Mesaverde Frontier Pierre Morrison Mesaverde Casper Pierre Frontier — Cloverly Mowry — Cloverly Embar — Tensleep 9 Cloverly Cloverly Mowry — Cloverly Frontier — Cloverly Cloverly 58 — Blue Spring 59 — Red Spring 60— Wlldhorse Butte 61 — Lucerne 62— Nelber 63 — Sand Draw 64 — Waugh 65 — Wagonhound 66^ — Enos Creek 67— Little Grass Creek 68 — Gooseberry 69 — Fourbear 70 Pltrhfork Tensleep — Madison Etoibar — Tensleep BJmbar — Tensleep Frontier — Cloverly Frontier — Cloverly Frontier — Cloverly Frontier — Cloverly Frontier — Cloverly Frontier— Cloverly Mowry — Cloverly Mowry — Cloverly 71 — Spring Creek 72— Frost Ridge Mowry — Cloverly Frontier 74— Teapot 7R North Lusk Embar (Mlnnelusa) 7fi Cofll Preek Frontier Casper Frontier 79— Big Hollow 80 — Saratoga 81 — Muddy Creek 82 — Big Sand Wasatch Pierre Fort Union Chugwater Fort Union Tensleep Benton Chugwater Frontier Sundance Wasatch Frontier 83 — Rock Springs Frontier Embar — Tensleep 85— Wallace Creek Eagle — Frontier Madison ? 87— Bates Hole 88 — Goose Egg 89 — Iron Creek 90 — Pine Dome 91 — Sundance Dakota Embar — Tensleep Dakota Gas Embar — Tensleep Benton Dakota 93— Platte River 94— Wheatland 96- Meridian 96— Tolteo 97 — Medicine Bow 98 — Simpson Ridge 99— Baxter 100— Castle Creek 101 — Sweetwater 102 — Upton 103 — South Lusk 104— Bitter Creek Pierre Benton Tertiary Dakota 9 96 POPULAR OIL GEOLOGY. these are the Gulf Coast fields of Texas, Louisiana, and Mexico; the Lima field of Ohio; and the greater part of the Wyoming fields. - Three types of domes may be recognized. These are Structural Domes, Saline Domes, and Volcanic Necks. Structural Domes. Dome structures which are the simple result of fold- ing or arching of the rock of the earth's crust are "Struc- tural Domes". STRUCTURE CONTOUR MAP OF LAMB ANTICLINE AND TORCHLIGHT DOME (Nos. 5 AND 6. RESPECTIVELY, ON PLATE I) AND STRATIGRAPHIC SECTION Ths oulciops o< sands ere mapped aF sand:*ones By Chtrlu ^ Lupton Scale ee^oo Figure 38. Structure map of Basin Oil Fields. POPULAR OIL GEOLOGY. 97 r^^^^^ Structure contours (lines of equal altitude) on 'top of P^*ZL_|GreybuM sand. Numbers show distance above WGas well * !■*■ level. Contour interval. ZOO feet -^Dry hole Figure 39. Greybull Oil Field. (U. S. Geol. Sur.) Wyoming, because of its complex geological structure, has a great number of such domes. Most of these are really "structural highs" on well-defined anticlines. Be- cause of the great interest in these structures at the pres- ent time, tlioy will he discussed in some detail. Figure 25 sliows a structural section of an ideal dome and also its structural cimtour map. On the map the structure is slmwn by contours one himdred feet apart. A number of terms are defined on the figure such as major and minor axes of diiniG, and height of dome. The contours are 98 POPULAE OIL GEOLOGY. SECTIONS SHOWING OCCURRENCE OF OIL AND GAS IN SOME OF THE ROCKY MOUNTAIN FIELDS. (Modified After Hares.) [Correlations approximate and sections incomplete. o., Oil; g., gas; +, seeps or small production of oil or gas.] System Spring Val- ley and Labarge. Big Horn Basin. Lander. Central Wyoming. Wasatch. +0. Wasatch. White River. + Tertiary. Wind River Wind River. + ? Bvanston. Fort Union. Absent or concealed Fort Union. Tertiary (?) Lance or Ho. Lance. Adaville. Meeteetse. Lewis. g Mesaverde, or Gebo Eagle. Mesaverde Mesaverde. Teapot, -f Parkman. S Hllliard. Cody. Pierre Basin. Mancos. (+0.) Steele. Shannon, o. s o S Niobrara. s Carlile. Cr )lorado. Frontier, o. Frontier, o. Torchlight. Peay (o.g.) Frontier. Wall Creek, o. + ■Peay. + O Aspen, u. Mowry. o. Mowry. Thermopo- lis. g. Therm opolis. Bear River, o. Cloverly. g. GreybuU Dakota. Dakota. -|- Beckwlth. Lower Cre- taceous (?) Lower Cretaceous Shale. Conglomerate + Cretaceous (?) Morrison, g. Morrison. Morrison. + Jurassic Twin Creek. Sundance Sundance. Sundance. + Triassic. Chugwater Chugwater, -\~o. Chugwater. + Permian. EJmbar + Embar. o. Embar. g. \ Pennsylva- nlan. Tensleep Tensleep. u. Tensleep. + Amsden. POPULAR OIL GEOLOGY. 99 SECTIONS SHOWING OCCURRENCE OF OIL AND GAS IN SOME OF THE ROCKY MOUNTAIN FIELDS. (Modified After Hares.) [Correlations approximate and sections Incomplete, o., Oil; g., gas; + , seeps or small production at oil or gas.] System Douglas. Black Hills Boulder, Colo. Florence, Colo. Tertiary. White River. O.K. Laramie (7) Port Union. Tertiary (?) Lance. Fox Hills. Fox Hills. Fox Hills. Trinidad. 7. o Pierre. Parkman (7) Shannon 7 + Pierre. + Pierre. Hygiene, o.g. (0.) Pierre. (0.) ous. Niobrara. Niobrara. Niobrara, o. Niobrara. s Benton. +o.g. Wall Creek 7 Mowry. (o.?) Carlile. + Benton, o.? Carlile. + O 6 Greenhorn. Greenhorn. o O Graneros. Mowry. o. Graneros. "Cloverly." 0.+ Dakota. + Dakota. + "Dakota" + Puson. + Lakota. Cretaceous (?) Morrison. Morrison. Morrison. Morrison. + Jurassic Sundance. Sundance. Trlasslc. Chugwater. Spearfish. Lykins. Minnekahta. Permian. Porelle (7). Satanka 7 + Casper. + Opeche. Lyons. Minnelusa. o. Pennsylva- nlan Pahasapa. + Fountain. EJnglewood. 100 POPULAK OIL GEOLOGY. SECTIONS SHOWING OCCURRENCE OF OIL AND GAS IN SOME OF THE ROCKY MOUNTAIN FIELDS. (Modified After Hares.) [Correlations approximate and sections incomplete, o., Oil; g., gas; + , seeps or small production of oil or gas.] System Western Colo. San Juan, Utah. Grand Co., Utah. Green River + Tertiary. Wasatch e.g. Tertiary(?) Mesaverde. o.g. Mancos. + Cretaceous (?) Jurassic Triassic. Permian. Pennsylva- nian. Dakota. + Flaming Gorge White Clift. L,a Plata. Dolores. Mochcopie. Goodridge. o. Green River. + Wasatch. + Mesaverde. Mancos. -f Dakota. McElmo. + La Plata. Pecos Valley, N. M. Red Beds. Delaware, o.g. POPULAK OIL GEOLOGY. 101 closely crowded