Structure of Typical American Oil Fields, Volume II

Edited by Sidney Powers


The Stephens field, discovered in 1922, has, produced 3,137,448 barrels of oil to January 1, 1928. The estimated future production is 2,175,000 barrels. It is estimated that the ultimate average acre-yield will be 1,875 barrels. The production is mainly from the Buckrange sand, the basal member of the Ozan formation, but a small volume of oil and gas is obtained from the Nacatoch sand. Both producing horizons are in the Upper Cretaceous. The structure of the field is a southeastward-trending structural nose, limited on the north by a graben. The lenticular structure of the reservoir sand has determined the distribution of the oil.

  1. Page 1
    1. Page 1

      The Stephens field, discovered in 1922, has, produced 3,137,448 barrels of oil to January 1, 1928. The estimated future production is 2,175,000 barrels. It is estimated that the ultimate average acre-yield will be 1,875 barrels. The production is mainly from the Buckrange sand, the basal member of the Ozan formation, but a small volume of oil and gas is obtained from the Nacatoch sand. Both producing horizons are in the Upper Cretaceous. The structure of the field is a southeastward-trending structural nose, limited on the north by a graben. The lenticular structure of the reservoir sand has determined the distribution of the oil.

  2. Page 18
    1. Page 18

      In the four oil fields of the Santa Maria district, namely, Casmalia, Cat Canyon, Lompoc, and Santa Maria, the reservoirs have been formed in the rocks where the oil and gas originated. The oil occurs in cross-faulted anticlines in which the faults have influenced the movement and location of the oil. In the Santa Maria district the oil comes from the diatomaceous Monterey shale of Miocene age. Although the diatoma-ceous shales have been commonly considered the source of the oil and gas, more recent studies have indicated that these highly organic sediments may have been deposited under conditions that would preclude their contribution of any hydrocarbons.

    2. Page 23

      The Ventura Avenue oil field is located in Ventura County, California, 2 ¼ miles north of the city of Ventura, in the Ventura River valley. This field has the reputationof being the most difficult field in California in which to complete a deep well. The topography of the field is very rough, embracing elevations from 100 to 1,100 feet. The Ventura anticline is 16 miles long with Ventura Avenue field at the center. The anti-cline plunges in both directions from the center of the field and is characterized bysteep dips on the flanks, which range from 300 to 600;. Production comes from the Picoformation, of lower Pliocene age. The field has six oil zones, but practically all production comes from the deepest zone, the Lloyd. The Lloyd zone has a known thickness of 2,600 feet, with the bottom of the zone as yet not found. The Ventura Avenue fieldhas at present [February, 1928] a production of 57,000 barrels per day of 20° so gravity oil, from 113 wells. The field has produced, since its discovery in 1915, up toJanuary 1, 1928, approximately 44,000,000 barrels of oil and more than 130,000,000,000 cubic feet of gas, yielding approximately 1 gallon of gasoline per 1,000 cubic feet of gas, and should ultimately produce 250,000,000 barrels of oil and 600,000,000,000 cubic feet of gas.

    3. Page 44

      The first drilling for oil in the Elk Hills commenced in 1910. The first well to pro-duce oil was completed in June, 1911, at; a depth of 4,000 feet. At the end of June, 1928, the total production was 96,199,914 barrels. The surface beds, aside from alluvium, belong to the Tulare formation of uppermost Pliocene age and are divided into upper, middle, and lower zones, altogether 730 feet of fresh-water sand,; marl, and clay. The subsurface beds are thicker and, in addition to the lower Pliocene, include Miocene formations. Maricopa diatomaceous shale (Miocene) is supposed to be the source of the oil. Surface structure, reflected by topography, is an elongate dome with closure of 450 feet. Subsurface structure much steeper than the surface indicates a closed dome in the eastern field, in the western field, and in the Hillcrest area. Anticlinal conditions have influenced the accumulation of the oil and gas; but sand conditions, more than position on structure, have influenced the volume of production.

    4. Page 62

      Long Beach, located in the Los Angeles Basin, has produced more oil than any-other field in California in the seven and one-half years since its discovery. A new sand was found in 1927 and exploited in 1928. Because of the location of the field in a city, a very rapid, competitive drilling campaign has followed the discovery of each successive oil zone. The present campaign has led to the preparation of a state report, an abridgment of which is presented as a typical example of one of the prolific anticlines of the district.

  3. Page 75
    1. Page 75

      The Florence field occupies a strip 3 miles wide on the eastern limb of a geosyncline. The oil occurs in fissures in the Pierre shale. The general dip throughout the field ranges from 2° to 5° westward. The eastern boundary of the field is a steep monocline that brings the productive beds to the surface. The western boundary coincides approximately with the occurrence of a heavy sandstone overlying the Pierre shale. Possibly the removal of the sandstone allowed the fissures to open and the oil to accumulate. Thus the accumulation may be as recent as present topography.

    2. Page 93

      The producing structures of northwestern Colorado are: (i) Iles dome, (2) Moffat or Hamilton dome, (3) Tow Creek anticline, (4) Thornburg dome, (5) Rangely dome, (6) White River dome, and (7) Hiawatha dome. Other seemingly favorable structures have been drilled and found barren. The producing formations range in age from Jurassic to Eocene. Oil and gas accumulation in northwestern Colorado is evidently caused by anticlinal structure. The nature of the hydrocarbons in the different structures and the lithology of the strata in which they occur indicate that the causes of accumulation were not common to all and that the folding and uplift to which they were subjected may have been factors in forming the oil and gas from the original organic material as well as being the agents of accumulation.

  4. Page 115
    1. Page 115

      The cross sections, maps, and other data presented in this paper give the essential facts about the Centralia district in south-central Illinois, the Martinsville pool in east-central Illinois, and the Francisco pool in southwestern Indiana. In the Centralia and Francisco areas, pronounced domes in the Pennsylvanian beds mark similar but more pronounced domes in the underlying Mississippian beds. In the Martinsville area, only a slight suggestion of the lower Mississippian folding is shown by the overlying beds.

      In general, the oil accumulation has taken place on the high parts of the several anticlines and domes. Locally, irregular sand conditions have modified this relation so that the limits of the producing areas do not exactly conform to the structural contours.

  5. Page 142
    1. Page 142

      The Virgil pool is one of the early pools to produce from the “Mississippi lime” in Kansas. Since 1916 the pool is estimated to have produced 5,000,000 barrels of 370-410 Bé. gravity crude from small long-lived wells located in an area of more than 1,000 acres. The pool is on a well-defined closed anticline which has been the governing factor in the accumulation of the oil.

    2. Page 150

      The Madison oil field is a part of one of the “shoestring” lines of production in Greenwood County, Kansas, which produce from Bartlesville sand lenses of great linear extent. The pattern and shape of the lenses, their double convex cross section, and their distribution with respect to paleogeography indicate that they represent sand bars and tidal delta bars formed by waves, currents, and tides near shore lines. Some of them may represent stream-channel deposits.

      Structure as represented by surface beds, the base of the Kansas City formation, and the top of the “Mississippi lime” seem to conform but to be without definite relation to Bartlesville sand deposits except that these lenses occur between and on the t sides of “Mississippi lime” buried hills, with the exception of the Seeley, Clark-Wick, and Shambaugh pools. Inasmuch as Bartlesville sand bodies are lenticular and are surrounded by shale which may have been the source rock, they are excellent oil reservoirs.

    3. Page 160

      The El Dorado oil field is the largest in Kansas and one of the largest in the United States. Until its discovery in 1916, little oil had been produced in Kansas. Since that time the state has been one of the leading producers of petroleum. The accumulation of oil and gas is due to the existence of a buried anticline over which the younger rocks have been folded a lesser amount. Oil and gas are found in these younger rocks, but the major production of oil has come from the Ordovician at the unconformity between this system and the Pennsylvanian.

      The anticline, with a total structural relief of approximately 1,400 feet, is typical of the “Granite ridge” of which it is a part. Faulting and most of the folding is confined to the pre-Pennsylvanian rocks, although there is closure of 150 feet on the surface beds. Because of the erosion which took place after the major uplift, the lower part of the Ordovician “Siliceous lime” is in contact with the upper part of the Pennsylvanian Cherokee formation, the unconformity being measured by the absence of ap-proximately 1,400 feet of sediments. The stratigraphy of the pre-Pennsylvanian is typical of that of south-central Kansas.

  6. Page 168
    1. Page 168

      The development of the Pine Island deep sands followed the exhaustion of the oil from the so-called “Woodbine” sand.

      The Glen Rose limestone is found in the Pine Island field immediately below the “Woodbine” sand at an approximate depth of 2,300 feet. The Washita-Fredericksburg sediments were deposited and eroded from the crest of the dome but occur around the flanks of the Pine Island uplift.

      The Trinity group in this paper is separated into upper Glen Rose, 200 feet; anhydrite zone, 450 feet; lower Glen Rose limestone, 900 feet; and red shale and sand zone, 2,000 feet.

      The main structural features of the region are the gentle folding of the Upper Cretaceous, which involves the entire area of the northern Sabine uplift and the more intense folding of the Comanche. The latter is confined to the Pine Island field. No faulting of any considerable magnitude is present.

      Three oil zones and one gas horizon have been developed to date in the Comanche sediments of Pine Island.

      The field has been outlined by dry holes, and the possibilities of deeper production are yet unknown.

    2. Page 183

      Caddo is the oldest oil field in Louisiana and was discovered and almost wholly developed before geology became an essential part of the oil business. The writer believes that, although the so-called “Woodbine” sand, the main oil-bearing horizon, may be in part the equivalent of the Woodbine formation of Texas, it also includes several sands both above and below a pronounced unconformity between Upper and Lower Cretaceous rocks and is in part Tokio and in part Washita in age.

    3. Page 196

      The Homer field, discovered in 1919, has produced more than 56,000,000 barrels of oil to date, and it is estimated that the ultimate production will total 64,000,000 barrels. Expressed in terms of acre yield, the production to date has been 24,600 barrels per acre, and the ultimate production is estimated at 28,000 barrels per acre.

      The Homer dome has a diameter of about 9 miles and a structural relief of 1,100 feet. The producing area comprises 2,300 acres at the apex of the dome. The dome is traversed by an east-west trending fault of the normal type, with the downthrow toward the south. The maximum throw of more than 500 feet coincides with the highest part of the dome. The angle of the fault plane ranges from 400 to 500.

      The oil is obtained from two sands in the Gulf series of the Cretaceous. The Nacatoch sand is productive throughout the field at depths ranging from 675 to 1,150 feet below sea-level. The Oakes sand produces oil on the south side and salt water on the north side of the major fault. The depth of the oil-producing sand ranges from 1,750 to 1,850 feet below sea-level. This erratic distribution of the oil in the Oakes sand is ascribed to upward migration along the fault plane, whereby the oil, which under normal conditions would have been trapped in the Oakes sand on the north side of the fault, migrated upward into the Nacatoch sand on either side of the fault.

      The Trinity group of the Comanche series has not been tested in this area but is believed to contain promising oil- and gas-producing horizons.

    4. Page 229

      The Bellevue oil field, in northwestern Louisiana, has produced in five years 8,500,000 barrels of 19.30 Bé. gravity oil from the Nacatoch sand, of Upper Cretaceous age, at a depth ranging from 300 to 400 feet. The field lies at the apex of a broad dome having a closure of about 800 feet. The accumulation of the oil is directly associated with a series of tensional faults. The faults in the Upper Cretaceous range in throw from 20 to 250 feet, but in the Lower Cretaceous a central horst has been faulted up 800 feet. Recently a deep well on this dome has penetrated much older beds than any hitherto encountered in Louisiana.

  7. Page 254
    1. Page 254

      The Kevin-Sunburst field is in Toole County, Montana, near the Canadian border. This northernmost field in the United States ranks second in oil production in the Rocky Mountain region. The producing structure is a dome on the north-plunging end of the Sweetgrass arch. The principal oil-producing horizon is at the unconformable contact of the Ellis (Jurassic) and the Madison (Mississippian) limestones. The principal gas-producing horizon is the Sunburst sand (Lower Cretaceous). Although there is no oil production on the top of the dome, it is believed that local folding in areas of porosity has influenced accumulation. The nature of the unconformable contact at the principal producing horizon also affects accumulation.

  8. Page 269
    1. Page 269

      The Kevin-Sunburst field is in Toole County, Montana, near the Canadian border. This northernmost field in the United States ranks second in oil production in the Rocky Mountain region. The producing structure is a dome on the north-plunging end of the Sweetgrass arch. The principal oil-producing horizon is at the unconformable contact of the Ellis (Jurassic) and the Madison (Mississippian) limestones. The principal gas-producing horizon is the Sunburst sand (Lower Cretaceous). Although there is no oil production on the top of the dome, it is believed that local folding in areas of porosity has influenced accumulation. The nature of the unconformable contact at the principal producing horizon also affects accumulation.

  9. Page 290
    1. Page 290

      The Hewitt field is the second largest field in southern Oklahoma. It is an example of an anticline overlying a buried hill. The rocks at the surface are Permian Red-beds. The oil is found in sands of Pennsylvanian age.

      The discovery well in the Hewitt field was located on the basis of surface geology. Later development, however, proved the subsurface “high” on the top of the first Hewitt sand to be considerably north of the well.

      The maximum production was reached in the month of September, 1921, when the daily average was 43,902 barrels. At the end of 1927 the field had produced 19,786 barrels per acre. It is estimated that at the end of 1941 the total yield per acre will be 27,301 barrels.

    2. Page 300

      The Cromwell field occurs in a belt or zone of en éelon faulting as expressed in the surface sediments which are composed of sandstone and shale belonging to the Francis formation of Pennsylvanian age. The surface irregularities and faulting are believed to be a reflection of subsurface folding, and possibly subsurface faulting. The Cromwell sand (Lyons sand) of Pennsylvanian age has been the source of practically all of the oil. The “Wilcox” sand, which is one of the sand members of the Simpson formation of Ordovician age, has produced a small amount of oil. The Cromwell and the “Wilcox” sands are found at average depths of 3,400 feet and 4,150 feet, respectively. The migration of oil up the dip from the west has been intercepted by two subsurface structural features, namely, a fault with more than 214 feet of displacement and a dome with 70 feet of closure. Production bears a close relation to these structural features, and there would have been a closer relation had local sand conditions not interfered.

    3. Page 315

      The Greater Seminole district, comprising the Seminole, Searight, Earlsboro, Bowlegs, Little River, Pearson Switch, St. Louis, Mission, and Maud pools, had a total production previous to January i, 1929, of more than 275,000,000 barrels of 400-gravity oil since the discovery in July, 1926. This is an average recovery of 15,055 barrels of oil from each of the 17,700 producing acres, and the area is producing 400,000 barrels of oil per day (January, 1929).

      The stratigraphy, structure, and geologic history are similar to the other major “Wilcox” sand pools of northern Oklahoma. Crooked holes, pre-Pennsylvanian faults, and rotary drilling have complicated the details of the geologic record. All of the pools are producing from anticlinal structures, many of which are reflected in the sur-face formations as minor folds, flattenings, and changes of strike.

      A chapter by Ira H. Cram of The Pure Oil Company gives an idea of the detailed geological problems in the district.

    4. Page 362

      The Delaware Extension pool is a long, narrow sand lens projecting westerly from the north end of the Nowata pool, Nowata County, Oklahoma. The pool was drilled up in 1910 and 1911 and has produced to date approximately 4,000,000 barrels of oil gross. The oil comes from the Bartlesville sand at a depth of 800 feet on the east end and 1,200 feet on the west end. Geologically the pool is entirely a sand-lens condition and is productive regardless of local structure. The conditions suggest that the sand lens is a buried river channel with similarities to the east-west shoestring pools of Kansas.

    5. Page 365

      The Depew area of Creek County, Oklahoma, is southwest of Bristow and includes two small pools and scattered clusters of wells. Surface structure is mapped with some difficulty owing to the fact that the sandstones and shales have weathered to a heavy soil cover with few and widely separated rock exposures. The eastern half of the area shows uniform westward dip, but the western half is broken by a series of en echelon faults with two small anticlines in Sections 8, 9, and 16. Subsurface structure in the Poor Farm and Depew fields shows small, gently dipping anticlines with the main axis north-south. Subsurface structures mapped on the Hogshooter lime, the Checkerboard lime, the base of the Layton sand, the base of the Bartlesville sand, and the top of the “Wilcox” sand, vary but little, but show a westward shifting of the axis of the fold. Production in the area is from the Layton, Cleveland, Prue, Dutcher, and “Wilcox” sands.

    6. Page 378

      The field here described, located in the southwest portion of T. 25 N., R. 8 E., Osage County, Oklahoma, produces oil from three formations, each bearing a different but definite relation to the geologic structure. All of the reservoir rocks are salt-waterbearing off of the local folds and oil-bearing on the higher parts of the closed structures. The field furnishes an excellent example of oil and gas accumulation governed by the principles of the anticlinal theory.

    7. Page 396

      The Cushing oil and gas field has produced nearly 300,000,000 barrels of oil since the completion of the discovery well in 1912. This amount is exceeded only by two other continuous fields in the United States. Accumulation of oil in the field is due to the presence of an anticline 20 miles in length. The producing area comprises 34 square miles. The average yield per acre to January 1, 1928, was 12,993 barrels. Previous publications relative to the Cushing field have not discussed in detail the unconformable relation between the Pennsylvanian strata and underlying rocks. At the Drop right dome, the Bartlesville sand (lower Pennsylvanian) rests on the Arbuckle limestone (lower Ordovician). This unconformable condition is present but less pronounced throughout the entire field. The pre-Pennsylvanian rocks on the east limb dip at a rate of 150. The west flank dips at a rate of less than 20. Several erosion cycles have affected the rocks in the Cushing district. The fold was probably present as an anticline at the end of Arbuckle time. Local history of movement cannot be traced during Ordovician, Silurian, Devonian, or Mississippian time. In early Pennsylvanian time the Cushing anticline was again uplifted. Subsequent erosion of the newly formed anticline resulted in the typical concentric distribution of outcrops about the anticlinal axis. The base-leveled anticline was later covered by the advancing early Pennsylvanian sea. Gentle uplifting occurred contemporaneously with the deposition of the Pennsylvanian rocks. The predominant west dip of surface beds throughout the region suggests a westward tilting of the Cushing anticline at some time after the deposition of the Pawhuska formation, outcroppings of which occur in the Cushing field.

  10. Page 407
    1. Page 407

      The Bradford oil field is of peculiar interest for several reasons. It is located about equidistant between the place where oil was first discovered in America and the famous Drake well. Its 85,000 acres of continuously productive territory from the Bradford sand, its 25,000 producing wells, and its fifty-five years of productive history make it one of the most outstanding oil fields of the world. It has received much publicity because of the successful use of water-flooding for increasing oil recovery within the past twenty years. The field was opened in 1871, and the peak of production was reached in 1881, when 23,000,000 barrels of oil were produced. The present production is about 3,700,000 barrels per year.

      The stratigraphie column of the Bradford oil field is limited to the Paleozoic. The principal oil-producing horizons are in the lower part of the Chemung formation of Upper Devonian age. The reservoir rocks are very fine-grained and tightly cemented sandstones. The most important sand, the Bradford, has an average thickness of 40 feet and an average porosity of approximately 15 per cent.

      Two anticlines, plunging southward, and converging northward into the Knapp Creek dome, with a closure of approximately 2 50 feet, have been the dominating factor influencing oil accumulation in the Bradford sand. This structure was also a primary influence in the accumulation of oil and gas in the minor productive sands, although the irregular depositional character of these minor sands has been an important -contributing factor in limiting production.

      Bradford oil has an average gravity of 45.50 A.P.L and is widely known for its high-grade lubricating fractions. Gas wells were rare in the original development of the field. On the Knapp Creek dome and at intervals along the crest of the anticlines, the upper part of the Bradford sand was a gas “pay.” The original rock pressure was presumably subnormal, but data on this are indefinite. The Bradford sand thins out on the east edges of the pool. Elsewhere edge water is present. Encroachment has been so very slight that from existing operating records it is impossible to establish any definite rate.

    2. Page 443

      Scenery Hill, a small village in West Bethlehem Township, Washington County, Pennsylvania, 25 miles southeast of the famous McKeesport field, was the scene of unusual activity in the spring of 1927, when the first gas well was completed in that field. Since that time thirty-six wells, sixteen of which were dry holes, have been drilled within a radius of 1 mile.

      Local domes located on a plunging syncline afforded an ideal condition for the segregation of gas, oil, and water. Unfavorable sand conditions caused many dry holes.

      Twenty wells produced 1,500,000,000 cubic feet of gas, with original rock pressures varying from 1,000 to 1,200 pounds. Production was largely from the Fifth sand. This compares on a small scale with the McKeesport field production of 22,000,000,000 cubic feet of gas from approximately 800 wells.

      Production reached its peak during November, 1927, when fifteen wells produced 454,600,000 cubic feet of gas. By August, 1928, there were only four producing wells, sixteen having been abandoned. The four active wells produced only 3,556,000 cubic feet of gas in July, 1928, these being operated on a vacuum.

  11. Page 451
    1. Page 451

      Oil accumulation on salt domes is either in super-cap sands, cap rock, or lateral sands. West Columbia is an example of a salt-dome oil field which produces only from lateral sands. One 20-acre lease has produced 620,000 barrels an acre in eight years. The Texas Company's Abrams No. 1 was completed on July 20, 1920, and for six weeks flowed at the average rate of 26,500 barrels per day of pipe-line oil.

    2. Page 470

      Stephens County, in north-central Texas, is situated on the axis of the Bend arch, one of the most important buried structural features in Texas. The most widespread occurrence of oil in the Bend series, of basal Pennsylvanian age, has been found in this county. Oil is also produced from sands in the Strawn formation, above the Bend. The control of oil accumulation is essentially anticlinal.

    3. Page 480

      The Yates field, eastern Pecos County, Texas, is on the crest of a bifurcate domal fold developed in the Permian “Big lime.” Subsurface folding in the Permian rocks is reflected by a similar anticlinal feature in the surface Comanche limestones. This dome, on the southwest margin of the Saline Basin geosyncline of West Texas, is a marginal fold on the general line of folding which extends through Upton and Crane counties. Production is from porous limestones near the top of the “Big lime.” The prolific production of oil is, in large part, due to the high degree of porosity of the limestones under the influence of high hydrostatic pressure of the water immediately beneath the oil.

    4. Page 500

      The Big Lake oil pool, located in the southwest corner of Reagan County, Texas, and opened by the discovery well in the Texon zone on May 28, 1923, was the first major oil field found in what is known as the “West Texas” district. The remarkable producing capabilities of its wells greatly stimulated geologic investigation and intense wildcat drilling throughout West Texas and southeast New Mexico. This has resulted in opening several prolific oil pools in a region formerly not considered seriously in estimates of our future petroleum reserves.

      Four distinct oil zones have been developed in the field. Two, the Shallow and Texon, seem to belong in the Choza member of the Clear Fork formation, Permian in age. The Third and Fourth have been developed in the deep well (University i-B) of the Texon Oil and Land Company at depths of 6,284-99 feet, and 8,520-25 feet, in probably the Strawn and the basal part of the Bend, respectively, both formations being Pennsylvanian in age, with the probability that the deeper zone is pre-Pennsylvanian. This well not only possesses an exceptional record for sustained rate of. increase of daily oil production from the Fourth zone after drilling operations had ceased, but it is also the deepest oil-producing well in the world and the deepest boring ever drilled for any purpose. The well opened this Fourth oil zone on December 1, after the manuscript for the original paper had been submitted, on November 11, 1928, for publication; but a description of the well's producing activity and character of the oil from this deep zone is given in an Appendix under date of January 31, 1929.

      The pool is closely related to a low anticlinal dome in the surface beds (Comanche), that is a reflection of a much more pronounced dome in the Upper salt beds (Permian) and a dome of still greater amplitude in the Texon discovery oil zone (Permian).

      The pools in both the Shallow and Texon zones are encircled by edge water, thus conforming to the applications of the “anticlinal theory” of oil and gas accumulation. It is believed that the pool in the Texon zone has been trapped while the oil was migrating laterally up the dip from the west and northwest, and that the character of the oil and gas in the Shallow sand suggests they may have migrated upward from the Texon zone pool along the plane of the fault immediately on the east side of the dome. Further, it suggests that the source material of the oil and gas in the Texon zone is indigenous to the dolomitic limes of the Permian.

      Up to October 1, 1928, the total production of the field was 36,238,451 barrels of oil-35,210,344 from the Texon zone and 1,028,107 from the Shallow sand, or 97.16 per cent and 2.64 per cent, respectively, of the total from the field.

      Many new wells remain to be drilled to develop fully the proved leases for the Texon, Third, and Fourth zones.

    5. Page 542

      A buried ridge or series of buried hills, known as the Red River arch, in northern Texas and southern Oklahoma, extends from northern Denton County, Texas, west to central Foard County, Texas. A number of productive geological structures are located on this arch. The Petrolia dome is the oldest of these fields and one of the most pronounced structures. Drilling has revealed that beneath the producing horizons in this field lies a series of thick limestones of Ordovician age, supported by a core of igneous rock; also, that beds of only two formations, Permian and Cisco, extend completely over the crest of the dome, but that those of Canyon, Strawn, and possibly Bend are deposited on the flanks. The chief source of production is near the base of the Cisco. Thick bodies of water sands are found in the lower formations around the edge of the field. One distinct unconformity is known to exist. This is between the Ordovician and beds of overlying formations. The Petrolia field is an excellent example of the relation of petroleum accumulation to anticlinal structure.

    6. Page 556

      Oil-producing conditions in this shallow field are typical of those existing in. other fields in this part of Brown County, Texas. The sand producing the high-gravity oil from a depth of about 1,300 feet is lenticular. It is stratigraphically located about 50 feet below the unconformity between the Canyon and Strawn formations of lower Pennsylvanian age. The interruption of the normal northwest dip found in this field is thought to be due more to differential settling than to folding or faulting. Contour patterns based on the top of the Palo Pinto limestone and on the top of the producing sand are shown to bring out the conclusion that contours based on the top of a lenticular sand body do not show the true deformation but, instead, show only the shape and ex- tent of the sand body. Porosity and the amount of true sand in the producing horizon have been the most important factors in the accumulation here. Structural deformation is considered, secondary.

    1. Page 571

      Even though West Virginia is the state where the anticlinal theory received its earliest practical application, later developments have proved that the state also contains the outstanding examples of synclinal oil pools. This is especially true in the southern part of the state, where such important synclinal pools as the Tanner Creek field of Gilmer County, the Rouzer pool and the recent Granny's Creek pool of Clay County, a part of the Blue Creek and Clendenin pools of Roane and Kanawha counties, and the Big Creek pool of Lincoln County are located. In the central part of the state the Copley field of Lewis County and the Wolf Summit fields are the major synclinal fields. Some of the synclines are closed structures; others are open.

      The following are the important sands which produce oil from synclines: Maxon, Keener, Berea, Big Injun, Weir, and Gordon.

  12. Page 577
    1. Page 577

      The Elk Basin oil and gas field on the state line between Wyoming and Montana is on a large anticline in formations of Upper Cretaceous age. Oil production comes from sands in the Frontier formation, and gas from the sands of the Dakota group. The structure is broken by three sets of normal faults with displacements ranging from a few feet to 700 feet. The south end of the field is an excellent example of the accumulation of oil in fault blocks. The field was discovered in October, 1915, and the total production to January 1, 1927, was 8,120,000 barrels. The field is now being revived with a unified gas drive. There are untested possibilities for oil and gas in deeper formations.

    2. Page 589

      The Salt Creek oil field has produced 209,619,275.48 barrels of oil since its discovery in 1889. It ranks as one of the largest oil fields of the world and still produces 50 per cent of the light oil of the Rocky Mountain region. The field has two new producing sands and several deeper horizons that remain untested. The development map of Salt Creek and Teapot domes is posted to October 1, 1928.

      A subsurface contour map and cross section show that the relation of oil accumulation to structure is in general accord with the anticlinal theory of accumulation. With the exception of the lower Sundance sands the entire Salt Creek field is producing to capacity. The production curve of the Salt Creek field will continue to show a decline.

    3. Page 604

      Lance Creek oil and gas field, discovered in 1918, is on a large anticline. Structure has controlled the accumulation of oil and gas. Production is from sands of the Dakota group (Cretaceous). The First, or Muddy, sand yields oil in small amount in a limited area on the crest of the fold, but the principal production is from the lower sands of the Dakota group. In these sands, gas in large volume is found throughout a large area, and a very narrow strip of oil territory borders the gas cap on the south and east. Because of steeper dip, the oil-bearing zone in these sands is probably much narrower on the north and west flanks than on the others, and has not yet been found by drilling, though there seems no reason to expect it to be absent. The water table originally plunged eastward, and production was obtained at the east end of the field down as far as the limit of closure, but farther west production was never found so low structurally. The gravity of the oil is 41.8° Bé. The average recovery of gasoline from the natural gas is 1.54 gallons per thousand cubic feet. To January, 1927, the field had produced nearly 3,500,000 barrels of oil.

    4. Page 614

      Rock River oil field was discovered in May, 1918. The oil comes from the sands of the Dakota group (Cretaceous). Accumulation has been controlled by structure, but the water table plunges nearly 900 feet from the south to the north end of the field. Production holds up better in wells on the flanks of the structure than in wells higher structurally. The gravity of the oil is approximately 370 Bé. Production to date has been more than 10,000,000 barrels, and it is thought that possibly as much more will be produced in the future.

    5. Page 623

      The Grass Creek domal structure is one of the most important of Rocky Mountain fields. It has several producing horizons of both paraffin and asphaltic oils. These are briefly discussed. Maps show the structure development at several periods including Tensleep and Embar (Pennsylvanian), and pre-Jurassic and Frontier (Cretaceous). No theoretical discussion is included.

    6. Page 636

      The commercial oil and gas pools are on crests of closed anticlines and domes except in the General Petroleum field, where oil is found in variable shaly sandstone beds on a pitching anticline without structural closure. The oil sand of the G. P. field (G. P. sand) is not productive elsewhere even on closed structures.

      Commercial oil is found in the Mowry shale on the crests of the three sharpest folds-Little Lost Soldier, Wertz, and Ferris. It is not found in the Mowry shale on the gentler folds or elsewhere. Seemingly the maximum fracturing and other mechanical effects peculiar to the crests of sharp flexures are necessary to the formation of the shale oil pools or pockets.

      The productivity of the structures, other factors being equal, is in close relation to the extent to which they are fractured and faulted. Burial of the productive sand beneath a great thickness of shale is equivalent to diminution in faulting, since the faults may be sealed or may not persist to great depths. The more numerous and open the faults, the greater the tendency toward an oil pool or to barrenness through more or less complete leakage. The fewer and tighter the faults, the greater the tendency toward a gas pool or to barrenness through lack of migration and accumulation.

      With the Lost Soldier and many other oil and gas fields of the Rocky Mountain region as confirmatory evidence, it may be said that, in the post-Paleozoic strata of the region (i) water in an upper sand is not indicative of what is to be expected in lower sands, whether oil, water, or gas; (2) gas, as the predominant product in an upper sand, means that lower sands may be expected to be primarily gas sands; and (3) oil, as the predominant product in an upper sand, indicates that lower sands are likely to be primarily oil sands.1

      • 3J. S. Irwin, “Faulting in the Rocky Mountain Region,” Bulletin Amer. Assoc. Petrol. Geol, Vol. 10 (1926), pp. 127-28.

  13. Page 667
    1. Page 667

      This paper is intended to summarize and correlate the results of the papers in cluded in the two volumes that comprise the symposium on geologic structure held by the American Association of Petroleum Geologists. The examples of various types of structure that are cited are drawn largely but not entirely from the symposium. Although, on casual reading, many of the papers may seem to depart in some particulars from recognized structural principles, petroleum geologists are not misled by the seeming “exceptions” into supposing that conditions really conflict with the principles. Careful studies have proved that the accepted relationships of oil and structure prevail universally, subject to the control of other fundamental criteria. The advance of our science during the last few years emphasizes the existence of many factors that were formerly unsuspected, any or all of which may affect the position of oil on, or in relation to, favorable structural areas. Every so-called “exception” is found to clinch the structural principles more firmly than before, and we can go forward with greater confidence despite seeming difficulties and can more keenly appreciate the pitfalls and the means for avoiding them.

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