UC BERKELEY MASTER NEGATIVE STORAGE NUMBER 03-67.43 (National version of master negative storage number: CU SN03067.43) MICROFILMED 2003 UNIVERSITY OF CALIFORNIA AT BERKELEY LIBRARY PHOTOGRAPHIC SERVICE REPRODUCTION AVAILABLE THROUGH INTERLIBRARY LOAN OFFICE MAIN LIBRARY UNIVERSITY OF CALIFORNIA BERKELEY, CA 94720-6000 COPYRIGHT The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted materials including foreign works under certain conditions. In addition, the United States extends protection to foreign works by means of various international conventions, bilateral agreements, and proclamations. Under certain conditions specified in the law, libraries and archives are authorized to fumish a photocopy or other reproduction. One of these specified conditions is that the photocopy or reproduction is not to be "used for any purpose other than private study, scholarship, or research." 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The application of the Anticlinal theory of oil ana gas to prospecting 1920 BIBLIOGRAPHIC RECORD TARGET University of California at Berkeley Library Master negative storage number: 03-67.43 (national version of the master negative storage number: CU SN03067.43) GLADIS NUMBER: 184785379C FORMAT : BK AD:991006/FZB LEVEL:b BLT:am DCF:a CSC:d MOD: EL:7 UD:030604 /MAP CP:cau L:eng INT: GPC: BIO: FIC: CON: ARCV: PC:S PD:1920/ REP: CPI: FSI: ILC: 1:0 040 CUScCU 090 SbDISS.O'NEILL.GEOL 1920 100 1 O'Neill, Frank, E. 245 14 The application of the Anticlinal theory of oil and gas to prospecting 260 $c1920. 300 [11], 57 p. ;$c29 cm. 502 Thesis (B.S. in Geology) --University of California, Berkeley, May, 1920. | 610 20 University of California, Berkeley.$bDept. of Geology and Geophysics$xDissertations. 690 0 Dissertations, Academic$xUCBS$xGeology$y1911-1920. Microfilmed by University of California Library Photographic Service, Berkeley, CA FILMED AND PROCESSED BY LIBRARY PHOTOGRAPHIC SERVICE, UNIVERSITY OF CALIFORNIA, BERKELEY, 94720 DATE: 7/03 REDUCTION: 10 X or PM-1 3%."x4” PHOTOGRAPHIC MICROCOPY TARGET NBS 1010a ANSI/ISO #2 EQUIVALENT 56 32 oedl a Il 2.0 Laan l= l= iid nis a MR T T MTs 4 A eu fn a un ol 16 18 ld El hd dh 1 ; | 192.0 | Page EAE rr Development of Anticlinal Theory - -I.C. White - 1 Application of the Anticlinal Theory = = = = = = 5 The Anticlinal Theory of Naturel Gas = = - - - =~ 7 Surface Indicetions for Oil and Gag = - - - - =~ 9 Strategraphic Relations of Petroleum = = - - - = il Structurel Relations of Petroleum = = = = = - =~ 11 Movement of Oil in the Birailg » = = = = = = « « 12 THE APPLICATION OF THE ANTICLINAL THEORY The Capillarity Concentration of Gas and Oil - - 14 OF OIL AND GAS TO FROSPECTING Studies in the Applicetion of the Anticlinal Theory of Oil and Gas Accumulation = - - - = 22 More Recent Statement of the Anticlinal Theory - 24 O Movement in POrous ROCKS = = = = = = = = = =» = = 24 The Coalinga District = = = = = = = = = = = = = 27 iy Relation of Oil to Structure - - = = = ~- ~- -== 36 LIBRARY COPY The 0i1 City Field = =~ = = = = = = = a a = =o = 36 The Kreyenhagen Field =~ - - = = = = = = = = = = 38 The Bast Side Field ~~ - = =~ = = =» = = = = = = = 39 Zhesis for Phe West Side Field =- - - = =~ = =~ = = = = = = = 40 Bs D. Degree The Kettleman Hills =- = = = = = = = = = = = = = 41 % Y, A oy) Sunset Oil Region - California = = = = = = = = = 42 ' 4 The McKittrick Field = = = = = = = = = = = = = - 43 Phe Monterey = = = ww = = = = = = = so =.= == 43 The Santa Margarita ~~ = » =» = = = = =» = == =» 43 Midway Field =~ =~ » =» mn» m= =» = wu == === 45 Sunset Field - - - = =~ = = = = = = = 2 =-w .--_—_---- 46 The Lost Hills “mee. -- 48 Salt Creek 0il Field - Wyoming Structure - - - - - - 50 The Salt Creek POOL =~ = = = = = = = = =u =m = = =» = 51 General Structure of Big Horn Basin - - = =» - -» - ~- 52 O11 and GEE = = = = = = = «= = =» ww ww w--n=- 54 DEVELOPMENT OF ANTICLINAL THEORY In testing the anticlinal theory of oil and gas with reference to prospecting, the following information is taken from a paper by liz. I. C. White* who is, in reality, the discoverer of the theory and by whom the theory was tested thoroughly in many Bastern fields. Mr. White discovered the characteristic accumu- letion of oil and ges in anticlines while employed by an eastern company to do reseerch along the line of oil and ges accumuletion. The theory was immediately accepted by Professor Bdwerd Orton, at that time one of Ohio's most emminent geologists, and applied to the oil fields of Ohio. Dr. Orton has expressed the ideas of the theory as follows: Structure is the essential element in the accumu- lation of large quentities of either oil or ges, for if the rocks lie nearly horizontal over a large areas we find, when we bore through them, "A little oil, a little ges, a little water, & little of everything, and not much of anything"; while if the rock reservoirs be tilted considersbly, S0 that the small quantities of oil, gas, and water in all sedimentary beds cen rearrange themselves within the rocks in the order of their specific grasvities, then and then only cen commercial quentities of each accumulate, provided the *White, I. C. Geol. Soe. America, Bull, Vol. 3, , 1892 “Dm reservoir and cover are good. The anticlinal waves which traverse the great Appalachian plateau westward from the Alleghanies and practically parallel to those mountains present just such structure as the theory requires in the N. Y., Pa., South=- ern Ohio, and West Va. oil and ges fields, while the more ancient flexures in northern Ohio and Indiana account for the large accumulations of oil and gas in the Trenton limestone of those states. The Florence (Colorado) and other oil fields in the far western states and territories have this tilted rock structure, and the same structure is plein in the Cenedien oil end gas fields, according to Selwyn; while other geologists who have studied the foreign oil fields report ah identicsl geological structure there. This theory so simple and consistent with well known physicel laws, as well as so harmonious with the facts of 2€01087, was heartily welcomed by most of the oil and gas operators, and by nearly all geologists that have given any thought to the matter, as a satisfactory solution of the geologic problems connected with the oil and gas accumulations. A few heve attempted to relegate the greet principle of structure to a subordinate position, but the facts have pointed so conclusively to its great value that opposition has been greatly overcome at last, whether convinced or otherwise. “Su Guided by this theory kr. White in 1884 located the important gas and oil field near Washington, FPennsyl- vania; slso the Grapeville gas field along that greet arch by the same name in Westmoreland Co.; and the Belle Ver- non field on the lionongahela river. On the same theory he located end mapped out for Mr. J. M. Guffey, the cele- brated Taylortown oil field of Washington Co. months before the drill demonstrated the truths of his conelusions and on this Mannington-lount Morris belt a derrick was built to bore for oil on one of his locations at Feirview more then 5 years before the drill finelly proved that his loestion was immediately over one of the richest pools of 0il in the country, and before the drill had shown that there was any oil in this portion of West Virginia. These are only a few of the positive fruits of the theory to which we can point; the negative results in condemning immense sarees for both oil and gas being even more import- ant in preventing unnecessary expenditure of capital where a search for either gas or oil would have certainly been in vain. An important corollary, drawn from the "anticlinsl theory" of gas and oil, and announced as probably true in an article by lr. White in The Petroleum Age for March, 1886, was that the pressure under which the oil and gas in any rock or field are found is of artesian origin; or in other alle words that the initial pressure in any oil or ges field is messured by the pressure of a column of water equal in height to that which rises from the same rock when water is struck instead of oil or gas. This was announced as the most probable theory in the paper referred to, and Professor Orton has since demonstrated the theory to be true in Ohio with reference to the gas pressures in the Trenton limestone. Dr. Orton proved thet the pressure in many of the fields in Ohio was equivalent to the head of water standing at the level of Lake Brie. The pressures obtained by lir. White in the oil and gas fields of Ohio and West Virginia checked splendid- ly ageinst the elevations below tide. The following data was compiled by kr. White in eastern fields: Field Feet below tide Pounds per sq. in. Gas in Pottsville conglomerate at Mannington 200 to 300 350 to 400 Gage in Mount Morris sands at liount Morris and Mannington - 700 | 500 to 550 Gas in Kount Liorris sand at Blacksville 600 - plus Gas in Mount Morris sand at Harrisville, West Virginia 1000 680 " Gas in Gordon sand . near Pittsburg 800 Gas in Gordon sand near Waynesburg | 1300 " wii APPLICATION OF THE ANTICLINAL THEORY Working upon the hypothesis that gas pressure was due to acolumn of water and therefore must be the same at various points in eny limited area where the rocks lie at the same depth below the sea level, lir. White de- cided that the oil deposit in the Liount liorris oil belt would extend across the country slong the strike of the beds in a pool comparsble to a lske or string of lskes should the rocks not be equally porous at every point. Hence, he concluded it would only be necessary to fol- low the outerop of any ecsily recognizable bed in that series where the oil was developed in order to determine with approximste accurscy, many miles in advsnce of the drill, the location and width of possible oil territory. For this purpose he was fortunste in finding two beds of coal whose outerops could be followed many miles. He made an accurate survey locating the top of the Waynesburg coal bed as to elevation at meny different points. He found thet wherever the Waynesburg coal had an elevation of 970 feet above tide they found gas and where it was 870 feet above tide they found salt water. Thus, knowing the dip he wes able to compute the possible width of the oil pool by the funetions of the angles of the right triangle, using the difference between the elevation of the coal bed over the gas and its elevation ley 870 feet _. . _. Llev. 970 fret. _ _ _ _. aif gw over water 88 one leg. This he did carefully and then traced the outerops into the vacinity of Mannington forgetting all else except his theory. The nearest well was twenty miles from the point picked for drilling. The course thus marked out was so crooked and passed so mueh farther to the west than the practical oil men thought was possible for the oil belt that the hypothetical belt was the subject of much joking among the 0il men. And only after much persuasion was he able to get capitalists to invest at such a point. Pinally, on October 11, 1889, the drill penetrated the top of the "Big Injun" oil sand and & splendid showing of oil wes obtained. After the Mannington test well was drilled there were about 200 wells drilled along the belt between Mennington and kiount Morris, the belt which had been mapped by Mr. White &s being possible productive terri- tory. Not more then 5 of these wells have been totally dry. This is a very small percentage for a large field for oil sands vary in porosity and numerous cases have been found where the porosity changed so repidly that on a favorable structure a dry hole has resulted within a few hundred feet of a gusher of 15,000 barrels per day. 1. ge le THE ANTICLINAL THEORY OF NATURAL GAS In 1883 lir. White was employed by a Pittsburg firm to meke investigetions concerning the accumulation of natural gas and while meking this investigation he noted that every large gas well was located at the crest of an upfold of one kind or another. This led him to believe that the accumulation of gas was relsted to earth movements. When he investigated the synclines he found that they furnished little or no gas but in many cases much salt water was found. Thus connecting up in his mind the commercial accumulations of nstural gas with upfolds and arches, lr. White set about testing the theory in a practical way by condemning and locuting gas terri- tory. The general results were to confirm the anticlinel theory. But while we find grest wells of gas and oil on anticlines we cannot conclude that all anticlines contain gas and oil. There are certain limitstions to the possibility of finding large gas wells on anticlines. The arch in the rock must be one of considerable magnitude. A coarse, porous rock of considerable thickness, or, if & fine grained rock, one that would have extensive fis- sures and thus in either csse capable of serving as a reservoir for gas must lie benesth the surface at such depth that the gas cannot escape at the surface but still Be close enough to the surface to be profitably penetrated with the drill. (Given by lir. White as 500 to 2500 feet.) The area where great gas flows might be obteined is con- fined to those underlain by a considerable thickness of bituminous shale. Pair gas wells may be obtained down the dip from the axis if the dip is sufficiently rapid and especially if the slope is slightly crumpled. In regions where there ere no well marked antielinals good wells may be obtained if there is a feirly repidly dipping stratum with ter- race structures along the dip. In the Pennsylvenia and West Virginia oil fields the drill has shown that sll of the great gas wells are located along the anticlinals and up folds, and where an apparent exception to this rule occurs we find a cross cut depression is the disturbing cause, and hence the seeming conflict is the strongest confirmetion of the real essence of the anticlinal theory, which, condensed and simplified in the fewest words, means that structure is the main factor in the search for great gas wells. om URFACE INDICATIONS FOR OIL AND GAS The chief types of surfece indications are the following: l. 0il seepages. a. Outerop of oil bearing stratum at the surface. bP. Where the oil has escaped through a crevice or fault. 2. Natural gas springs. 3. Outerops of sands impregnated with tar or bitumen. 4. Dikes of bitumen. 5. Bitumenous lakes. Non-cheracteristic indications: 1. Salt water and salt deposits. 2. lud volcanoes. 3. Hydrogen sulphide escaping. Surface indications are not essential in the location of oil since many fields, such as those of Ohio, Indiana and Illinois, show an absolute lack of surface jndications. However, when the surfsce indications are found, it is evidence that there was at one time, if not at the present, oil in that locality but the structure may be such that the commercially important sccumulations are far from the indicetions noted upon the surface. -10- For the economically important accumulation of 0il there must be certain favorable structural conditions. The greater part of the world's petroleum has been found in sandstones and limestones but producing wells have been developed occasionally in shales and even in igneous rocks. Formations from which oil may be obtained by wells are spoken of as reservoir rocks. These seem in the majority of cases to be merely containers of oil, the Jan 0il having been genersted in neighboring strate and col- | lected in the reservoir rocks due to their porosity. The porosity of rocks is an essential factor in determining the capacity of the rocks to store oil. ll STRATEGRAPHIC RELATIONS OF PETROLEUM One of the principel reyuisites for a productive oil field consists of a porous reservoir rock overlain by en impervious cover. Usually the reservoir rock is sandstone, send or limestone and the cover shale. There are, however, exceptions to this rule. This covering rock is cslled the "cap rock" and is usually hard and impervious. It may be of lirestone and has been known to be of hard sendstone. The most widespread formation in Ohio and Indiana fields overlying gas and oil sands is the "Utica Shale" above the "Trenton" limestone. The Clinton sand of central Ohio is overlain in the same way by the Clinton shale. In the Louisiana fields a hard stratum of limestone acts as a cap rock. Cap rocks may consist of almost any relatively impervious formation. Where there is no cap rock the oil will soon lesk to the surfsce and disappear. Structural Relations of Petroleum Oil gas and water S10 COMEOULY found in a defi- nite relationship to each other. They are supposed to have been intimetely mixed at one time and due to earth move- ments, folding, ete. They have separated out by virtue of their different specific gravities. They occur in anticlines and domes with gas resting upon oil and oil “lB resting upon water. Where the strats sre perfectly dry the oil may be found at the bottom and in sueh cesses it may occur in synclines. Such is however & rather un- common occurrence. The ges, usually, in segregating goes to the highest available place in the stratum. Movement of Oil in the Strata There are three forces supposed to be mainly responsible for the movement of oil through rocks: 1. Gravitation 2. Capillary attraction 3. Difference in specific gravities Gravitation is prascticslly negligible owing to the grest amount of friction encountered by the oil in passing through the rocks. Capillary Attrection can teke place only in rocks having exceedingly small pores such as clays or shales and under certain conditions to be stated later. When these small pores contain water the oil cannot enter. This is why the csp rock of clay or shale serves so well as an impervious layer to the oil. (This will be dis- cussed further at another plsce in this report.) Difference in Specific Gravities - This seems to be the principal factor in the accumulation of oil, water and gas. Water seems to have assisted the 0il in moving -15- through the porous stratum until the gas came against the impervious stratum and the oil cushioned against the gas, the oil resting upon water. This has been the sequence in every case except where there was no water in the rocks (Ponnevivenis and West Virginia occasionally) and in such cases the pool of oil was found in the syncline. Conse- quently upon the examination of an oil field, one must determine whether or not the rocks are wet or dry. ld THE CAPILLARITY CONCENTRATION OF GAS AND OIL Porosity - The porosity of a formation would be independent of the size of the grains if all grains were of the same shape and size. This however is not the case in the geologicsel column and the porosity depends upon the amount of fine material thet is in the open spaces. It has been shown by Slichter that the porosity for a pile of spheres is sbout constant regardless of their diameters so long as the diameters are the same. The shape of the grain meterially affects the porosity, round grains leaving more open space than angulsr or flat grains. The thin plates of kaolin and the fine rlestic matter of clay fit quite perfectly when pressed together and it is probably this close fit due to the shepe and not to the size that causes the low porosity of clesy shale. The best sorted, lesst cemented sediments are the most porous. The porosity of a very fine grained rock mey exceed 10% if the grains are uniform size and discrete as in the so-called 0il shale discovered by Woodruff in the Green River forma- tion of Western Colorado and Utah. The rock has the magascopiec appearance of a tough cemented shale but in reality it is & consolidated eolcareous mud or fine mare composed of discrete angular microscopic grains of cal- cite with solid and liquid hydrocarbons in the interstices. 1B The porosity is the measure of the maximum reservoir capacity of the stratum. Capillarity - Capillary action varies directly as surface tension and inversely &s the diem. of the capillary. The surface tension of oil is sbout one-third that of water. Capillery Concentration - Since water has about three times the surfsce tension of oil, capillary attrsction must exert sbout three times as much pull upon it and since the pull veries inversely as the diam. of the capillary the water would tend to be drawn into the finest capil~ laries leaving the larger ones for the oil. The gas with no surface tension would tend to fill the largest pores. Moreover capillary attrection resists the movement of water from the fine to the lsrge pores with about three times the force thst it resists the movement of oil, hence the water would tend to displsce the 0il in small pores snd force it into the larger ones. The finsl result would be the concentration of ges snd oil in the largest pores end in fissures if present. This has been born out in practice in oil fields where the pores of the coarser greined rock contsin most of the oil while the pores of the sdjacent fine grained rock contain chiefly water. Any slow flow of water between shale and sand would tend to concentrate the coil in the sand and the water in the lbw shale. Probably the capillary force alone would be suf- ficient to displace the oil from the shale. In the ebsence of water the 0il would be drawn into the finest capillaries and would be widely diffused throughout the area and there would be no economically important concentration of the oil. 0il shale like those in Utah and Colorsdo could easily be formed by the oil impregnating layers of fine porous lirestone which it reached by ascending through fissures. This would have to teke place where the layers of limestone were dry. There is an upper and a lower limit to the diam. of tubes in which capillary sttraction can take place. In pure water there is no attresction in tubes above | 0.508 mm, diem. and in smooth fissures over 0.264 mm wide. 0il and gas are collected in these larger ones not because it is attrected but because water occupied the others. Crude oil has no attraction in tubes over 0.2 mm in diam. and in fissures over 0.1 mm wide. The minimum diam. is | somewhat uncertain but usually placed at 0.0002 mm for tubes and 0.0001 mm for plane fissures. Friction in the small opening slows down the flow; according to theory, capillery attraction must cease when there is not room for two or more molecules of water to pass through it together, that is, in csse of & fissure where the width becomes less than twice the radius of the “l= sphere of molecular action. The range of molecular action for weter equals 0.00005 mm. Capillery Pressures - The maximum theoretical pressures developed by capillary ection are those developed in the finest tubes in which capillary action is possible. These pressures have been calculated for the temperatures prevailing at varying depths by Johnson and Adams and accepting their assumptions, using 0.0002 mm &8 the mini- mum diameter for tubes we have these pressures tabulated below. Approximate Maximum Capillary Pressure ( Diam. of Pores, 0.0002 mm Temp. Gradient, 1 degree C per 30 m Depth in lieters Pressures in Atmospheres +100 15.0 +200 14.6 500 14.1 1.000 13.6 <.,000 12.1 5.000 7.8 10.000 1.0 20.000 0.0 The above shows that the maximum capillary pres- sure decreases about half at a depth of 5000 meters but owing to the fact thet in many oil fields the temperature «18 increases more rapidly as the depth increases we would find the capillary force decreesed by half at a depth of 3000 to 4000 meters below the surface. The change in surface tension of the hydrocarbons is much less rapid than thst of water for esch increment of temperature so that the surface tension of water is not much in excess of that of the hydrocarbons at great depths. Hence we would think that the capillary concentration of oil and gas must be effected within 4000 to 5000 meters of the ground surface. Oil in the deeper strata must remsin in its original dis- tribution unless concentrated at some earlier geologicsl period when the rocks stood at 2 less depth from the sur- face. The pressures shown in the previous tsble are not sufficient to give the pressures found in many of the oil fields and one cannot attribute these pressures to the capillary action. If however we assume the capillaries pores and fissures to be continuous, which is plausible, we might well attribute this pressure to the imperceptible outwerd translation of the rock fluid snd the pressure of the abyssasl gases. (The capillary penetration of the abys- sal fluids need not approach the base of the sedimentary strata to account for the incressed pressure in sends far above them.) However, the presence of chlorine in oil field waters, and the great amount of helium and argon in natural -l19- gas suggest that the upward migration in oil regions is more extensive than the excess pressure would require, and possibly some fluids of sbyssel origin may be pene- trsting far through the sedimentary strata. Time - In tubes epproaching the minimum capillary dismbter the flow from capillery action would be negli- gible, but in pores of 0.001 mm dismeter, which are of about the Same magnitude as the intergranuler pores in shele, the flow due to capillary action would be gbout 15 X 107° ¢.c. per year. In s rock contsining 10k pore spsce this would result in a flow of about 15 c.c. across egch square Cm. per year. Possibly 7 .ccC. per Square Ch per year correspond more closely to the fsctors imposed by ordinary clay shale. This would be sufficient to produce capillary concentretion in & geologicesl period but not in & short time. In 10,000 years the movement if continuous would smount to 700 m but this would not be continuous, as it would chenge in direction with pore diemeters and only smell distances could be traversed directly by cspillary pull. The fine shales probably gather the oil from its originel dissiminated sources and pass it on to the coarser figsures. Under the principles gdvanced the capillary flow of oil in wet rocks should tend glways towsrd the coarser or lsrger openings. It is not necessary to assume the movements in the pores are due to «20 - capillarity but there are doubtlessly other slow motions of underground fluids from some causes or other and any motion whatever will tend to concentrate the oil and gas in the lsrger openings, whether the motion be direct, reversed, or oscillatory becszuse the water would enter the fine pores with grester esse and would be dislodged with grester difficulty than the 0il or gas. Antielingl Theory. The oil and ges must be gathered in the sands by capillary concentrstion 2nd then the ges by difference in Sp. G. goes to the highest point of the sand. Due to friction there is some doubt about the oil rising by dif- ferences in Sp. G. glone but knowing thst where ges is pessed through weter and & bubble of gas touches a drop of oil the two unite, the oil enclosing the gas, we have reason to think thst the oil rises to the surrace due to assistence from rising ges and circulstion in the water and once at the water ges surface it is held there by the surfece tension, Thus we have the sccumulasting deposit of oil and g&s in the antecline. In this action the sur- fece tension has & tendency first to join like particles together and thereby the ges gathers until it will dis- place enough water to rise ageinst friction. This occurs with the 0il to & certein extent but the 0il requires some movement of the vweter to rise agsinst the friction. Where 2] STUDIES IN THE APPLICATION OF this motion is absent we may have the oll concentrated THE ANTICLINAL THEORY OF OIL AND GAS ACCUMULATION below weter as has been found in Some cases. Mslcolm J, lunn Places of Accumulation 1. In dry rocks the principal points of sccumu- 1stion of oil will be &t or nesr the bottom of the syn- clines or ot the lowest point of the porous medium, or &t any point where the slope of the rock is not sufficient to overcome the friction, such ss structursl terrsces or benches. 2. In porous rocks completely satursted with aceumuletion of both oil snd ges will be in the anticlines ( | or slong the level portions of the structure. iihere the ares of porous rock is limited the sccumulstions will occur at the highest point of the porous medium, and where aress of impervious rock exist in & generslly porous stretum the sccumulation will tske place below such im- pervious stop, which is reelly the top limit of the porous rock. 3. In porous rocks that are only pertly filled with weter the oil sceumulstes at the upper limit of the satursted area. This limit of ssturstion traces a level line around the sides of each structural basin, but the height of this line may very greatly in adjscent besins and in different sands of the same basin partial saturation “D5 is the case most generelly found, in which case accumula- tions of oil may occur anywhere with reference to the geologic structure; it is most likely, however, to occur upon sStructursl terraces as these places are favorable to sceumuletion in both dry and satureted rocks. Under all conditions the most probable locations for the sccumulstions of gas are upon the crests of ante- clines. Small folds glong the side of a syncline may hold a supply of ges, or the rocks may be SO dense that gas cannot travel to the gntecline, but will remain in volume close to the oil. 24 More Recent Statement of the Anticlinal Theory Whether the petroleum comes from within or below the shales it must pesss through them and to do this it must pass through the very small pores existing in "those relatively impervious beds. The nature and cause of this movement are not understood. Cepillary gsetion end grest rock pressure nay be suggested as csuses which aid in forcing the petroleum out from the shsles, but there are not sufficient deta on this subject to justify any scientific explanstion, It mgtters little what the ultimate source of the oil; the important fects are its occurrence now in the porous sandstone, its eirculstion through the rocks and the conditions leading to its accumu- letion in commercial deposits. Movement in Porous Rocks The porous rocks into which oil and ges enter mey be dry or they may be completely sstursted with water. In most cases it is probeble that a combination of these two causes exist - that the porous rocks are completely satureted with weter up to & certain level but above that point they are dry. The movement of the hydrocarbons | through the rocks will not be the same in the two cases and therefore esch comdition must be considered separstely. If small gquentities of oil and gas enter & dry porous rock at different points the 0il will flow down as long as gravity is sufficient to overcome the friction and capillary attresction. The ges will diffuse with the | | | | | air or weter vapor conteined in the pores of the rock. | 0il end gas entering & rock thst is completely setursted with weter will be forced up to the top of the porous stratum by the difference in the Sp. G. of the hydrocarbons and the water. Here the oil end ges will remsin if the porous stretum be perfectly level, but if it hes a dip sufficient to overcome the friction the perticles of oil and ges will gredually move up this slope, | the ges with its lower Sp. G. occupying the higher places. In case the porous rocks are partly saturated 8 combingtion of these two sctions will tske plece. The 0il entering above the line of complete saturstion will flow down to thst line end the oil entering below will be forced up to the top of the completely setursted portion. The statements given above are based on the assumption thet the 0il bearing rock is homogeneous through=- out snd that the oil will move with the same degree of freedom in every dipeation, This is rsrely the cese. Sandstones are noted for their irregulerity in composition gs regards both the size of the individual grains of sand and the meterizl which cements the grains together. It is obvious that any fluid will move more repidly through & coerse conglomerste irregulesrly cemented than through a -20 = dense, fine grsined sandstone, the psrticles of which ere thoroughly coated and all the interstices filled with impervious cement. If the oil besring rock contsins areas precticslly impervious, these aress, seeording to their size and position will be more or less perfeet barriers sgainst the movement of the oil or the gas. “Zl = The Coalinga District Recent quarternary: Alluminum Terrace Deposits es 89 59% as a» Pleistocene Pliocene : Tulare Etchegoin licKittrick Cenazoice o® 9% os se as Tertiary liiocene : $8 «8% @&% 2% 8% s% 8 ae = 8% 9% a» Santa. lergarita - as ae 8% wo eh «es S86 a=» .e a0 8% 5% a8 =» +. Vagueros Oligocene | et a . aP 8% a8 9% an Eocene : Tejon .e Upper Cretaceous - Chico lVesazoice Lower Cretsceous - KEncxville es ©8 ss as ss Juressic - Francisean (Associsted with some igneous) ——————— The formstions underscored above with the exception of certain igneous and metamorphic rocks associ- ated with the Frsunciscan, are of sedimentsry origin. With the exception of the grester portion of the pliocene and quaternary and of minor smounts of the esrlier tertiesry deposits, these sedirents are merine. They indicste that the grester portion of the srea included in the Coclinga field wes benesth the ses during periods occupying probebly the mejor portion of the time from the Jurassic to the end of the liiocene. Yet unconformeties sepsrating these forua- “iB= tions from one another show that intervals occurred during which no sediments were deposited, and that even with the enormous thickness of strata preserved the record is not complete. It is in generesl nesrer complete in the southern than in the northern district. Franeiscan Formation - Jurassic The Frenciscan rocks are characterized by the presence of serpentine which has been intruded into the sediments. The originel sedimentery rocks which are sand=- stone, shale and Jasper are much disturbed and occur in detached areass. They are mingled with glancophone octino=- | lite and other schists, serpentine and other metamorphic rocks. These Franciscan rocks are not known to contein any petroleum. ¥noxville - Chico Rocks - Cretaceous sbout 12,800 feet thick. These strsts sre hendled together s&s they show no distinet line of seperstion in this field. The Horse- town formetion is not known here. The Knoxville-Chico is sandstone, shale snd conglomerste Lower portion - Thinly bedded compact shale and sandstone. Upper portion - Massive drab concretionary ssndstone. The Enoxville~-Chico rocks sre divided into three divisions: lower, middle and upper. The Lower Division is 2000 feet of alternating thin beds of greyish black shele, shely sandstone and fine -29- sandstone of dark gray color. At the base of these there is a massive sandstone which forms the prominent ridge of Curry Mt. The total thickness of the Lower Division is about 3100 feet. The lower division is overlain by a heavy conglomerate. Middle Division ~- Resting upon the lower with the heavy conglomerate at its bese there is a series of alternating thin beds of dark shale and sandstone about 4800 feet. Upper Division - Concretionary sandstone in lower part; shales in upper part; thickness of at least 4700 feet. These strata grade into one another and seem to indicate continuous deposition. The ssndstone of this division is usually dvab, medium greined and not very hard. Contains numerous reddish brown concretions. The upper pert of this division is sheles end with difficulty dis- tinguished from the eocene beds overlying. There are two shales here separated by a conglomeratic sandstone. The lower shale bears some fossils. The uppermost shale, owing to its petroliferous character and similarity to the eocene beds is of interest. About 1200 feet thick and has some considerable admixture of send and sandstone and is a purple shale. Purplish brown, fairly hard, thinly bedded, both siliceous and calcareous clay shale, in which test of foreminifera are sbundant. Contains nodules of yellowish calcareous shale and grayish white limestone. Above the purple shale there are seversl hundred feet of dark clay and clay shale beds. Importance with Relation to Petroleum - Presumably the source of a large amount of light oil produced by the oil city field. | Tejon Formetion. (Bocene) 1600 to 1850 feet thick. Two parts: lower one =- sandstone in south and dark clay shale with sand in the north; upper one ~ light colored organic shale. These shales are whitish and purplish siliceous, argillaceous and locally calcareous shale. This shale is supposed to be the source of the oil found in the Tejon and later formations of the Coslinga district. The post eocene beds are petroliferous where associated with the Tejon and where it is absent they are dry. The oil has migreted upward from the Tejon and accumulated in the more suitable reservoirs afforded by the miocene beds. Vaqueros Sandstone (liiocene) Rest unconformably upon the Te jon of the eocene. From 5560 to 900 feet thick. Hard and soft sandstone and shale and conglomerate. This is underlain by the Tejon shale and overlain by the Sante liargarite shale. The vaqueros is the principal reservoir of the Coalings field. The 0il collects chiefly at its base. «3]l- Sante liargarita - Miocene (upper middle) seems to be the same as the Sante Margerita which was found ferther west. Fossil oysters and barnacles of very large size. The basal portion of this formation known as the Big Blue. This fossiliferous formation is overlain by 400 to 500 feet of alternating beds of fine sand, sandy clay, coarser sand and gravel up to the base of gravel zone on bese of Jacilitos. The Santa Margarita is about 1000 feet thick. This formstion is of great importance as forming an impervious cap (big blue) which has held the oil in the viqueros formation. Jacilitos (upper miocene) Sends, gravel and clay sbout 3500 feet thick. Productive in east side field only, due to approximity there to the Tejon. Btchegoin (uppermost miocene) beds of sand, gravel and clay about 3600 feet thick fossiliferous. Non=- productive. Tulare Formation (upper pliocene or lower pleistocene) Gravel, sand and clay, little consolidated with beds of freshwater shells, marls and limestone at base. 2400 feet thick. No traces of oil. Alluminum and Terrace deposits. Structure The structure of Mt. Diablo Ridge is anticlinal while the eesstern side is a greet monocline of sedimentary strate dipping towerd the Sen Joaquin velley. The general orientetion of the structure is N. 40 degrees W. There is considerable faulting in this field end folding. lMovements took plesce in pleistoce times which disturbed the tertiary and cretaceous beds as shown by their relation and the degree of folding in pliocene and early sleistocene. Other movements took plece before miocene times. Owing to resistance to folding the cretaceous strete has been faulted a greet deal. The tertiary however is folded more than feulted. There are many unconformities in the Coslinga field. Mein Lines of Structure The Coslings Antecline (60 miles long) in the northern part of the field is plunging N. Es. and in the southern pert it is plunging N. W. It is rether assymet- rical. The Coalinge Syneline is immediately west of the anticline. The fsults and folds in this section are curved end plunging. Varying locally in direction and amount of movements. Structure in Los Gatos Creek Here & broadly folded antecline of Cretaceous beds with a locally sharp axis plunges S. i, and N. E. of the flanks of these two ridges, towsrd the lower part of “BG Los Gatos Creek, where it is crossed by a oroad syncline . plunging N. W. into a section of White Creek end S. E. to -Plessent valley. Toward Pleasant velley it broadens out to form a part of the general monocline dipping toward the axis of Coalinga Syncline. Complicated faults occur along Los Gatos Creek. Jacalitos Hills Between Alcalde and Reef Ridge there is a de~- pressed area occupied by comparatively low rolling hills that represents the structural continuation of the old | Synelinal basin of Waltham velley. The Jacalitos Ante- cline plunges in both directions into the flanks of the Jacalitos Syncline. | Castle Lt. Feult Zone complicated feult zone | in the S. W. pert of the field. The movement here had precticelly cessed before Santas largsrite of liiocene was 1aid down @g shown by slight smount of folding in Sante Margarita. pyramid Hills Antecline in S. W. pert of fields and was formed long after cessation of fsulting of Castle Mt. Zone. Here the exposed rocks belong chiefly to the Knoxville-Chico, the lster formations having been eroded away . Awenal Syncline - West of and about parallel to the Pyramid Hills Antecline. | -34- Diablo Antecline - 5S. W. of avenal syncline, and is a steep fold plunging S. E. Its axis exposing Knoxville-Chico. The later formetions having been eroded away « Formations in which the petroleum occurs Petroleum occurs in five different formations in this district: 1. Purple shale memper of Chico (upper Cretaceous) 2. Tejon - eocene 3. vagueros - lower miocene 4, Santa liargarita - upper middle miocene 5. Jacalitos - upper miocene The oil in the first two is thought to pe primary while the 0il in the other three is supposed to have mi- grated there. The Chico 0il Zone The sandy zones in the lower pert of the purple ‘shale contein commercial quentities of oil on the Coalinge Anticline in the oil city field. Paraffin oil, usually about 33 degrees to 34 degrees Beume and is greenish color. Yield 4 to 75 barrels per well per day. Thickness of pro- ductive measure 15 to 60 feet. Tejon Oil Zone is known to contaln commercial quantities of oil only in the southern portion of the dis- trict where the oil has gsthered in the porous sandstone -3Dw of the lower member below the shales of the upper member in which it is supposed to have originated. Very light amber colored oil from 45 degrees to 48 degrees Baume occurs sparingly in the uppermost productive Tejon sands of the 0il City Field. Vaqueros is the principal 0il bearing formation of the Coalinga field. hers are three zones which are productive in the Vagueros. Black or dark brown oil 14 degrees to 31 degrees Baume aversge from 100 to 200 berrels per well per day. Santa Margarita - A stratum of sand carrying characteristic fossils of the Sents liargarita formation immediately overlies the Tejon in sections of the west side field is productive. Jacalitos is commonly oil bearing wherever it rests upon or is relatively near the Tejon which is the source. There are two zones here, one in lower part and snother about 200 feet above. These are separated by sulphur weter. The water in this field occurs in some- what isolated lenses. ~B6w Relation of 0il to Structure The coalinga District is divided into five separete fields as follows: l. 0il City field 2. West Side field 3. Bast Side field 4. Kreyenhagen field 5. Kettlemen Hills The following is given over to sctual fects obtained from drilling records and from reports from the fields and while in some cases these reports were scant it will be seen that in every case the oil is found accord- ing to the principles laid down by the anticlinsl theory. No other theory esn expleéin the consistent occurrence of oil and gas in anticlines, domes, terraces, monoclines and upfolds of all kinds. The 0il City Field The productive portion of the Oil City Field is nainly in the northern one-half Section 20 T 19 S RISE. This portion occupies the gentler slope of an antecline. Immediately below this area is & steeply dipping portion of the sane and operations in this portion of the field, which is the southern one-half of Section 20, have not been successful. The oil has migrated up this steep slope and become trapped on the gentler slope which acts like a terrace in the accumulation of oil and gas. These wells «3 = produced only small quantities of oil and were not profitable. Later, wells were put down southeast of these locetions, .at which place the dip had become gentler, and 0il was found in commercial quantities. There was much money expended in this field without any study of the structurel conditions and the first successful wells were located merely by chance. A few years after this the field was studied by the United States Geologicel Survey and a theoretical limit of the possible productive area based upon the structure with reference to the anti- clinel theory wes indiceted upon the geologicel map. Inasmuch as the actual conditions of saturetion of sands with water cen be had only from drilling, there wes a syncline included in this area. Actual drilling showed the sands to be fairly well satursted with water which excluded the possibilities of oil in the syncline leaving only the entecline to be fested. Drilling opera- tions under the guidance of this work by the United States Geological Survey have been successful and much loss of money snd time has been avoided by sinking wells in the favoravle locations. The theoretical limit of the pos- sible productive area originally extended as far south, along the flanks of the anticline ridge, as Guijarral Hill. This point is loceted upon the axis of the Coalinga enti- cline but the anticline southeast of this point plunges 38 = MN. W. end N, W, of this point it plunges S, E. The fact that the altitude of the anticline was such could be readily detected but the amount of this plunging was estimated at about 200 feet fall per mile. lore complete work brought out the fact that the plunging was nearer 1000 feet per mile. Owing to this discovery and the inability to definitely determine the actual structure beneath the hills the theoretical limit was moved about six miles N. Wo, at which point the line on the map crosses Anticline Ridge. The dip of the axis is so great that in all probebility the oil hes migrated up the dip. If, however, there is still oil in the flexure beneath the Gui jarral Hills 1 probebly could not be reached profitably with the drill. The Kreyenhggen field covers a narrow strip of territory on the eest side of Reef Ridge. A monocline dipping eest at a steep angle provides the possible trap for the oil and gas. This field is narrow, owing to the steeply dipping reservoir streta. However, this field has no impervious strata for a trap and the only trap available is the residual from the evaporated oil. It cen be seen that 0il in large quantities hes migreted up this dip and escaped at the surface. For this reason there is probably very little oil left in this reservoir. Had this condition been noted before drilling commenced much money could have ~39 - been saved that was spent in drilling. The anticlinal theory states that there must be an impervious strata or seal above and below the reservoir rock. Only in few exceptional cases has the residue from petroleum proved sufficient berrier on a steep dip to prevent the mein contents from escaping. Had the anticlinal theory been followed here the risk rate would have been known. The Bast Side field is located on the east slope of the Coalinga anticline. The eest flank slopes more gently than the west flank and thereby offers a better opportunity for the accumulation of oil. It, at the same time, owing to the gentler dip effords a larger drilling aree than the steeply dipping flenk. The oil from the west flenk migretes to the highest point in the anticline. Just before reaching tiis point the dip be- comes gentle and where this has occurred the oil has been found in commercial quantities. From this point the east flank resumes its homoclinal structure striking in a northeasterly direction and dipping to the S. BE. The productive area has been extended along the flank of the monocline to the NN. B., for a considerable distance from the axis of the anticline. The first drilling took place in Section 21, 22, 27 and 28 T 19 S RIBE and more recent operations have carried the productive area up to 3ec. 2, T 19 S$ RIBB. This extension has followed slong the flank dQ of the monocline. This field has been developed according to the enticlinal theory and has been a great success. The West Side field lies on the flank of a homocline which has & moderate dip to the esst. This field has been successfully extended to the south along the flank. The Blue Dismond well, which discoursged operations eve for a while but it was put down too near the outcrop of the petroliferous formation and was a failure. Late wells drilled down the dip from the Blue Diamond proved successful. The edge water in this field has been found to be in contact with the oil on the lower portion. of the flank of the homocline. The level of edge water is rising eech year due to the continued production of the oil from above the water leaving, thereby, new space into which the water rises. If we drill below this contact line between the oil and edge water we get nothing but water, while above the line we get oil with a little water perhaps. This smell amount of water is due to the deple- tion of the ges pressure by production;where the ges pressure is high the contact between the oil and water is usually sharp but where the ges pressure is low the water tends to channel through the oil in places. This accounts for the edgewater produced with the oil above the edgewster line. The encroschment of edge weter may cause the well to “ile be producing from both the oil and water levels and may in that way account for some of the water produced with the oil, The Xettleman Hills, which are underlain by the petroliferous vaqueros formstion according to indications are formed by an anticlinal fold. These Hills were reported by the United States Geological Survey as & fevorable loca- tion for oil in commercial quantities. Development has apparently proved this ststement to be wrong. There is little doubt that oil underlies the Kettleman Hills but it is not possible to produce it with modern drilling equipment for the section through the Hills will show that in order to reach the Vaqueros formation it is nec- essary to penetrate about 5000 feet of pliocene strata and about 2000 feet of the Santa lLagaritas formation, making the well at least 7000 feet deep. The deepest well in the Kettleman Hills seems to be about 4700 feet deep. Thus it is necessary to drill beyond the point from which it will be of econcmic adventege to produce. dB Sunset 0il Region - California Recent : + Pan: deposits, stream terraces Pleistocene 3 : McKittrick t: Santa Margarita Miocene : : lionterey Shale : vagqueros Sandstone Oligocene Eocene Tejon : Chico Cretaceous : Knoxville Jurossic Franciscan The above is & succession of beds in the NeXittrick Sunset region and with the exception of certain intrusives and metamorphic rocks in the Franciscan and of two areas of Basalt associated with the miocene beds, these formations consist wholly of marine and freshwater formations. In this region the Franciscan and Enoxville- Chico formations have been found to be unproductive, nor is the Tejon an importent source as it is in the Coslinga field. It possibly affords reservoirs for oil. The lionterey end Santa liargarita have proved to be the most importent sources of petroleum. From these the products have passed downward into the more porous sands and gravels of the underlying Vaqueros (lower miocene) and upward into the wd interbedded lenses of the Sante liargerite and also into the deposits of the McKittrick formation unconformably overlying the Santas liargerite and lionterey formations where it has lsrgely been retained until it has been tapped by wells. Through denudation or structurel dis- turbance there have been asphaltic products associated with the upper part of the licKittrick and more recent deposits. The LicKittrick Field - The formations involved in the licKittrick field are the diatomaceous shales of the lionterey snd Santa largarite formations, sandstone, clays and gravel of the licKittrick formetion and the wuaternsry grevels, sends, clays, travertine &nd asphaltum deposits. The Monterey - 3,000 to 5,000 feet of hard clay and dispmeceous shale, with some calcareous layers and gsendstone lenses. The Sente largerita - 1,500 feet of soft dieto- meceous shales locelly silicified to chalcedony in which are a few fine soft sandstone lenses and leyers. LeXittrick Formstion lies unconformebly upon the lionterey and Sents largerits and consists of nearly 2,000 feet of soft, dsrk colored shale, fine and cosrse pebbly send and incoherent cobbly layers. will The coarser basal portion of the MeKittrick is the productive oil zone of the field, the petroliferous strata being found throughout a thickness of 200 to 600 feet or more. The oil is struck meinly on the flanks of the Dabney end Shamrock anticlines. The Dabney anticline is overturned at one plsce in the southern end of the lic- Kittrick field. There is precticslly no water in these sands and the oil has to be pumped to a great extent practically entirely staept in the new wells. The gas sends above the 0il send have considerable pressure. In ceses where there is water the oil is found well up the flanks of the enticlines. This is seen in the eastern flank of the overturned Debney anticline. The oil sends sre overlein and underlain by the blue shale or shell. In the McKittrick snticline the oil is found along the flanks on the lL. I, side. The first work was done in the licKittrick field by shafts and open cuts in 1866 and this was done near the outcrop. About 1884 8 well wes drilled in S. EB. 4 Sec. 13, T. 30 5S. R. 21 E. and the oil rose about 100 feet in the pipe but the well never produced. There were other wells drilled at verious points away from the favorsble structure but these were feilures. Some of them gave showings of oil but none of them gave commercial quantities. The pro- ductive area is confined to the flanks and crests of -45- the several anticlines mentioned and desperate attempts to extend the proved area have feiled. The licKittrick field is smell in acreage but has produced heavily per acre. Midway Field ~- Here we have the liidway and Spellacy folds developed as subsidiary folds on the flank of the monocline on the esstern flank of the Temblor range. The axes of both anticlines are more or less unduleting end the dips on their flanks very from five degrees to twenty-five degrees. Here the best pro- duction and lightest oil come from the territory adjacent to the knobs of the snticlinal exes, especially nesr the knob which marks the beginning of the plunge of the axis toward the Liidwaey velley. This fect suggests that the accumulstion of 0il in this field is possibly controlled in part at leest by water. As we go down the dip awey from the axis of the anticline we come into areas charac- terized by unproductive wells and wells gone to water. The productive arees follow the exis of the Spellacy Hill anticline in 8 N. W. direction and then in Sec. 17, 7. 32 S, R. 23 E the productive eres turns more to the north end follows the Liidwey anticline. These two structures can be followed on the map by the trend of the plotted productive wells. willow There are & few wells gone to weter nesr the crest of the anticline but these wells are the result of top water due to poor "shut offs” end not of oie water. Much trouble has been met with in this field from weter treceable to improperly cemented water strings and lists of such wells are being published by the State liining Bureau for repeirs. Sunset Field - This field is located on the . Thirty-Five and Celifornia Fortune Anticlines and sub=- sidiery flexures all of which are developed on the flank of the great monocline on K. E., flank of Temblor Range. The wells here sre loceted on the flenks of the anti - clines and subsidisry domes end folds. The first work in this field was done about 1894 in the S, W. border of the field and the wells were sunk near the outcrop snd in shallow territory. Develop- ment extended the productive area northwestward along “the N, &., flank of Temblor Renge. The productive wells lying in a belt on the monocline which penetrate the mein oil send epproximetely between 600 feet sbove and 200 feet below sea level were the deepest wells until 1908. After this dete development took place further down the dip of this monocline and in 1910 the Lske View gusher was brought in. This well is situated on the flank of the monocline where the productive formation changes 4" = from a steep to a gentle dip. Such & location would be an ideal place for asccumulstion of oil and gas due to the slow movement of the oil escross the terrace and the relgstively rapid addition of oil from the down dip side. An examinetion of the latest maps from the Sunset region shows a number of wells drilled in the Midway velley in Sections 22, 23, 26 and 24 of T. 32 S, R 24 B, also in Sections 30 and 31 of T 32 5, R 25 E. and in Section 18, TT 31 S, R R56 BE, &ll of which pro- duced water. This field was examined by the United States Geological Survey and owing to the fect that this area wes determined to be synclinal predictions were mede that wells located there would bring water and little or no oil. Exploretion has sustained this view. Geologists who made the above report sglso reported on the Buens vista Eills, steting that the structural con- ditions were ideal for the sccumulation of oil and gas with’ reference to the gnticline passing through the hills. The shales of the lionterey snd Sante Lsrgarite were traced to such & point thet they were believed to underlie the licKittrick beds that form the surface of the hills and the chances for obtesining commercial quan- tities of petroleum there were reported as excellent. Future developments sustained their views as can be seen in Section 26 end 36, T 31 S, R. 23 E in which there -48- -iQe heave been put down about fifty wells. Those at the : ‘ . p y while in the southern srea the axis has emerged suffi- crest of anticline heve been gas producers while the ‘ Sw g P ciently to be within reach of the drill until it plunges others have been oil producers. n P S. Zs under the alluvium &t the southern extremity of | | the Lost Hills. The Lost Hills Phe areas in the Lost Hills were examined and the report was favorable to the production of oil in commercial quantities in that the monterey shale is | underlein by the Vagueros sandstone which sandstone furnishes much of the oil of the lMeKittrick end Sunset region. No indicetions were found of oil above the Sente Msrgerite but the stetement wes msde that such | was possible. Development in this erea hes shown that | the oil lies in the formetion known ss the mtchegoin sbove the Sante lMergerita. The occurrence of the 0il & at this horizon accounts for the shallow wells contrary to predictions. The formetion is enticlinel and the 0il is obteined from a nsrrow strip on eech side of the axis. These shellow wells are the result of the oil having migratea into the overlying formation rather than into the underlying vagueros. This is in accordance with the Anticlinal Theory in every aspect. It seems as though the petroliferous strats in the northern ares of the Lost Hills is beyond the reach of the drill SALT CREEK OIL FIELD - WYOMING Structure The Big Horn Mountains are flanked on the S. E. by seversl anticlines, arches of strata that rise like a series of waves, each higher than the last, toward the major arch that forms the mountains themselves. On the eesstermost, (the outermost) of these anticlines is the Salt Creek 0il field which obtains its oil principally from the Wall Creek sand. The pool in this sand occupies about seven square miles on the crest of an arch that, considered in its entirety covers several hundred square miles. The fold is not symmetrical for its crest is much nearer its western than its eastern limit. The width of the eastern limb of the fold, measured from the crest to the bottom of the adjoining syncline is about twenty miles while the width of the western limb measured from the crest to the bottom of the adjoining syncline is about one and a quarter miles. The Salt Creek Anticline is made up of three minor domes and two shallow intervening saddles. The northermost of these domes, the Salt Creek dome, is the largest and is outlined by the outcrop of the Shannon sandstone. The fact that the dip of the east limb of the Salt Creek anticline is very much gentler than the -Hl- dip of the west limb hes an important influence on the depth of the 0il sand below the surfesce. The axial plane of the fold slopes toward the east snd the crest of the 0il send, which in the Sslt Creek field lies sbout 1,000 feet below the surfece, is therefore about a quarter of a mile ferther east then the trace of the crest of the dome on the surfesce aes indicated by the dips. The Salt Creek anticline, in spite of its asymmetric cross section, is extremely regular in outline &s compared with anti- clines in other oil regions. The irregularities which do occur seem to be gentle swells on the sides of the fold and only tend to extend the 0il pool slightly in those directions. The Salt Creek Pool The principel source of the oil in the Salt Creek Pool is the Wsll Creek sand which, at the crest of the dome is sbout 1,000 feet below the surface and has a thickness of from 100 to 1285 feet. The distribution of the oil in this sand is dependent to a certain degree upon the relative porosity et different parts of the send. The porosity varies from about 7h to 25%. The totsl porosity is sbout 18% end the effective porosity is less than this, due to the cementing materiel in some places in the send. The distribution is, however, very -52= regular, there being no dry holes found within the limits of the pool, commercial production being obtained wherever the send is tapped within the limits of the pool. The edgewster level does not vary more then 150 feet all around the pool. The wells near the crest of the dome obtein a larger percentege of ges then those farther down the flenks but all the wells in the pool flow from their own rock pressure snd the flow continues for years without pumping. This flow is to be attributed to the pressure of the dissolved gas end the fact that all of the wells show this to a certain extent leads one to believe thet the ges is fairly well distributed over the field. The variation in the ges pressure in different parts of the send end slso the variation in the porosity cesuse some of the wells to flow inter- nittently, every thirty minutes or hour. From the surfsce to the send inside the rim rock there is nothing but shele. The wells ere shot with from 100 to 200 querts of Nitroglycerine, which greatly inproves their flow. General Structure of Big Horn Basin ~- Structure- ally the Big Horn Basin is & depression bounded on gll sides except the north by prominent upfolds which form the mountains that surround it. The grester number of the folds in this region are unsymmetricel, having steeper dips on one side than on the other. The folds become flatter near the trough of the basin and the general trend of the structure is along & line N 40 degrees W. There is some faulting in the area. wb 0il and Gas Mode of Qccurrence (Specific information ob- tained by drilling) The beds that have yielded most of the oil and gas in the Big Horn Basin are Cretoceous age and are parts of the Cloverly formetion, Thermopolis shale and Frontier formetion. Gas has been found also in the Morrison formetion. An oil seep has been noted at the base of the Chugwater formstion, slso in beds that may be psrt of the Amsden, Tensleep or Ember formetion. The results of drilling to dete show that the sands of the Frontier formation yield the grestest pert of the oil and thet the sends of the Liowrey shale end Greybull sand yield oil ss well &s most of the gas now produced in the besin. Other formstions et present offer no pro- spects for successful drilling. Areess that are structure- ally fevoreble should be tested to the depth of these formations before being sbandoned except in cases where erosion hes been so active as to cut the reservoir rock end thereby permit the contents to escape. The wells thet have struck large quantities of oil end ges in the Big Horn Basin sre near the crests of anticlines and domes. Of those wells drilled nesr synclines or where the beds are neerly flat over large 55 areas & few heve struck small guantities of oil and ges end a few have failed to yield oil, ges, or water, but most have yielded water. In severel of the productive fields on anticlines weter is found in sands both above and below the 0il &nd gas sand. ‘In general, the relation of gas, 0il and water in the snticlines in this are those demanded by the simplest interpretation of the sntielinel theory es set forth by Dr. Orton in 1886: "T¥ one of these sandstone streta filled with salt water, oil and gas and freely per- meable leterelly snd horizontelly for miles at a time were thrown into g system of low folds, what effect would this movement have upon the contents of the stratum? Would not a separstion of gas oil and weter be sure to follow, the ges finding its way to the summits of the srches snd the salt weter sinking to the bottom of the troughs? Such a result would be ineviteble under the conditions as~- sumed." According to the theory, if ges, oil and water are present in lerge quantities and if the sdjustment in the pervious bed according to the specific gravities of the substances were complete the ges would occupy a zone at the highest part of the folded beds &nd be limited be- low by the roughly horizontel upper surface of a zone of 0il. The oil, in turn, would be limited below by the approximately horizontel upper surface of a zone of water. If the proportion of gas were relatively low it is clesr that -56= all of it might be dissolved in the oil under existing pressures and the oil rise to the highest pert of the fold. The available informetion from the productive fields of the Big Horn Basin shows that in this region much less gas is present than is commonly associated with productive 0il pools. The limits of some of the productive oil pools in the Big Horn Basin are rather sharply defined and in the Gress Creek rool. After two years of development a sinuous line may be drawn which will separate the oil and water zones. The inner layer within which all wells which penetrate the productive part of the frontier formstion will yield oil with little if eny water, and the outer area within whose boundaries a well penetrating the pro- ductive horizon of the frontier formetion will yield water. Bach prominent enticline thet conteins oil sppeers to hold but a single pool. In the ares of the Greybull, Torchlight end Grass Creek the zones in the grolific sends that yield the oil extends much lower slong a pert of the flet besinward 1imb than on the steep mountainwerd limb. The besinward folds (where the strete dips without reverse to the Big Horn Basin) have proved to be by far the more productive of the two. The practicel absence of flowing wells in the Big Horn Basin may be contrested to the number of flowing -57- wells in the Salt Creek field and the reason for this may be the grester number of uptfolds adjacent to the Big Horn Basin, The Greybull Dome is approximately elipticel in shape with the smaller point to the N. We. The 0il occurs on the N. W. side of the dome and the gas about at the top or slightly to the NN. W. side of the dome. To the E, S, and S., W. we have water. There is opportunity for water to enter the send on the N. E. side about three or four miles from the dome and due to this force probesbly the oil has been pushed around to one pool on the I. iW, side. Much more work will heve to be done in the Wyoming fields to bring forth the conclusive evidence for or against the snticlinal theory. The work which has been done points favorably to the anticlinal theory and there is little doubt about the drill proving the theory in Wyoming eas it hes in every known oil field up to the present time. END OF TITLE