Show oil 01 1 possibilities of the rio virgin anticline antic line BY W E CALVERT A revival of interest in oil prospects in southwestern utah has recently taken place and at present one company is actively proceeding with test drilling and two others are said to contemplate early development the writer has had occasion to examine hastily this area of present operations and the following discussion is intended to outline briefly the main geological features having a bearing on the oil possibilities As indicated on the accompanying map the area in question is in washington county in the vicinity of st george access to rail is by stage through cedar city to lund on the san pedro a distance of nearly one hundred miles to attempt oil development in the district the r reform e f 0 r calls for a truly pio spirit with more obstacles to 0 overcome than usual ly IY obtains in connect tion with an oil ter prise i geology in common with t the southern utah j and northern arizona region the st george district presents geo of triassic age at the base is a grey member termed the Shine rump conglomerate which because of its relative hardness usually forms a prominent cliff see photo beneath these triassic beds are light colored to deep red shale and sandstone with minor amounts of limestone layers all of permian age and about 2000 feet thick next in turn is a formation known as the kaibab limestone the complete section of which is exposed in the cliff constituting the up thrown side of the hurricane fault a displacement that cuts the grand canyon and extends north to and beyond cedar member feet thick of fine grained sandstone with the lowermost feet comprising red and alternating blue gray crystalline limestone the three precede prec edini formations the kaibab the coconino anil the supai are of carboniferous age and make up what is known as the aubrey group of the pennsylvanian ref reference orence will be made later to this group in connection with its oil possibilities since it is from it that oil must be obtained if at all in ahe he well now drilling near st george or from those in contemplation in the district two marked structural features are dis M M e F V pt P r F mt 11 t Q ga im VY drilling on harrisburg dome by virgin dome oil company logical features that oan call be read with certainty as formations outcrop in a series of cliffs where every inch is bared to inspection due to dif ferent orential rent ial uplift and excessive later erosion a considerable thickness of paleozoic and strata are exposed and by going to io the canyon of the colorado about sev enty five miles distant the lower formations down to the crystallizes crystal lines can be seen en and examined in detail I 1 the youngest sediment aries exposed in the e vicinity of st george are of jurassic age e consisting of generally soft be beds ds of variable triable color comprising red and green ales gypsum and white limestone about 00 1209 OO feet thick in all next below are pink 1811 h to deep red sandstones 2600 2500 feet thick geologist salt lake utah city the kaibab is characterized by having a large percentage of its mass composed of a dense flint or chert which is probably in part a replacement of the lime and in part due to aggregations from fossil skeletal remains such as sponge spi cules underlying the kaibab is the coconino sandstone consisting of about feet of fine grained wh white ite sand the coconino is the lowest formation exposed in the st george district and information concerning still lower strata must be obtained considerable distan distance cei in the at a down the virgin possibly grand canyon or canyon southwest of st george in grand canyon the formation below the coconino supai and there it comprises the is known as member feet thick of an upper sandstones and a lower soft red played in the st george district one is the hurricane fault already cited and the other is a long upward fold termed the rio virgin an anticline ti cline the axial line of this fold is indicated by three long narrow ridges held up by the resistant kaibab limestone with paralleling vallies eroded SH the softer permian strata and encircled by a prominent cliff formed by the shin arup conglomerate each of the three ridges in reality represents an individual structure locally termed the harrisburg the washington Washingto nand and the bloomington domes see map therefore if oil is present in the district it will be confined to the three localities cited and not spread throughout the rio virgin anticline as a whole w hole the accompanying photographs show this relationship between present topography and the underlying rock structure As indicated by the cross section on the in map ap the rio virgin anticline shows that the pressure resulting in the fold was mainly from the south since the strata on tho the south limb are not steeply inclined whereas those on the north side are nearly vertical in a tudy study s of any particular area with respect to its oil po pose 1 mp lete knowledge is sought c ig several conditions not only one out but all of which must be present or oil will not occur in in that area or if occurring cannot he be econ comically omi cally developed first of all there must be a source of oil usually a shale contain ing organic matter secondly there must be a porous stratum in or not far above or below the originating shale into which tho the oil can pass and be stored thirdly there must be structural conditions such as an upward fold that permits localization of oil from a large area into a relatively small one fourthly there should be fairly com A of R 0 jirim ne larm p ip G sea 9 water saturation of the underlying rock mass or at least of the porous mem ber to cause movement of oil to its loci 0 of accumulation fifthly w with th the foregoing conditions condi tiong present it is necessary that the porous stratum constituting the oil reservoir have impervious material between it and the ground surface and yet be not so deeply buried that it lies beyond economic drilling reach of the five conditions of the five conditions cited that rela gelatin re latin tinz 7 aa waal li netom dome wa bieu wa v to structural conditions is the one concern ing which definite information can usually be obtained in advance of drilling however if the area under examination is in a field already tested or where the rock section below the surface can be seen not far distant another essential condition that 0 of origin of oil can be ascertained with considerable sid erable assurance likewise information can be gained relative to tile the occurrence of porous members and their probable depth at any particular locality As to the necessary factor of water saturation conclusions must be based on inference and not on di it should he be incidentally evidence understood that the foregoing conditions do not by any means cover every case but that each area presents its own special problems for study however the conditions affecting oil accumulation are simpler in the rocky mountain province than elsewhere and specific rules can be applied with considerable assurance chances of obtaining oil applying the foregoing criteria as cited district does not lead to to the st george a positive final conclusion but it does point to the fact that the chances of obtaining oil in commercial quantity are somewhat remote regarding the essential factor of 0 structure there can be no question since the rio virgin anticline or rather the three domes comprising that anticline pos besses no specially unfavorable feature As already stated however suitable geologic structure is only one of five necessary conditions dit ions the absence of any one of which medicates I the lack of commercial oil starting on the surface on any one of tha domes the drill will pass first through the kaibab limestone this formation can be considered neither a source of oil nor a reservoir for its retention after migration from some possible lower source since it is too siliceous to constitute a source and too readily permeable throughout to be a reservoir the underlying coconino sandstone is likewise certainly not a source and while it could readily absorb and possibly retain an upward migrating oil the writer has yet to see any indication of oil saturation in that formation moreover since these two formations kaibab and coconino are fully exposed in the vicinity of the rio virgin anticline it is highly probable that their meir character cna racier as those enose ex 1 postures is comparable to that to be found if t by drilling on the domes the upper thou V 1 I sand feet to be penetrated is thus weighed and found wanting so far as likely oil occurrence is concerned regarding the underlying supai formation one passes from certainty to infer inference rence since there are no nearby exposures of that formation such inference is based on r re e gional dional study and of the grand canyon section in particular in grand canyon the supai suggests by its character that it is not a likely source of oil the occurring in the formation are generally red or pinkish h showing that whatever organic matter they may have originally contained has been completely oxidized the lowermost one hundred feet does to he be sure contain lime members that might originate oil but the amount thus originating would be small and there is too large a proportion of sand in the overlying strata to permit localization of oil into a limited thickness the formations below the supai as shown in grand canyon need not be considered for they either could not be assumed as an originating source of oil or lie at too great gr a depth to be reached by drilling on th if one rio virgin anticline therefore could be certain that the supai and lower lowe formations occurring beneath the surface in in 1 the st george district are comparable age in detail to strata of the same geologic grand canyon it would be unreasonable ta expect oil in the former area it is efer inferred but only 0 k that such a similarity does exist infer in the drill can prove or disprove the ence to base h hopes 0 pes on a possibility ever appeals appeals to the writer as representing re presen geld ld undue 0 optimism for testing any n ne ew Is always attended with a considerable degree of risk even where all conditions appear favorable even granting that the supai formation beneath the rio virgin anticline is of an oil originating character there is still the uncertainty concerning underground der ground water conditions U unless there is water present and that under tic head oil would not be moved to the highest localities in the structure but would occur down the flanks wherever the water level would permit it to rest in that event ent it would probably be beyond t he i reach of the drill since the inclination of the e strata stratum carries any particular rapidly eidly from the horizontal in the san juall an oil field of southeastern utah the oil occurs caurs in the synclines syn clines instead of in the normal occurrence simply be cause of the lack of hydrostatic head cited and d similar conditions might well obtain in th e st george district however there s again ain the drill is the final arbiter and one can only theorize in advance of actual deni dem ost ration near virgin city occurrence of oil in well near virgin city some thirty five miles east of st george and the presence of oil saturated sands at the surface at various localities in the district have been advanced as favorable indications of oil at depth beneath the rio virgin ant anticline ieline As a matter of fact however these occurrences are not pert pertinent in the case since both the oil in the wells and the saturation in outcrops are from rocks above the kaibab limestone be bently that the old capitol petroleum fuel iron company has made arrangements for the construction of a railroad from lund to cedar city in iron county utah a distance of nearly thirty two miles for the purpose of opening up the coal and iron fields in that portion of the state the rord road to cost in the neighborhood of the new road will vill make connection with the main line of the salt lake route at lund it is stated that the bonds of the com 6 ba 7 9 A 15 18 16 aeto 30 0 T 20 21 Z 2 19 20 22 Z 4 ST laforge 30 29 2 7 25 T IW 32 az 35 36 A 4 V VIRGIN RIVER ANTICLINE washington COUNT 7 10 I 1 T UTAH 45 13 18 b X A B C 15 W sc 11 Y aa LT lati E R EVIE W 0 cross section on line AZ A Z ing in the basal portion of the permian the final conclusion is therefore that while occurrence of oil in the rio virgin structure is not impossible it is highly improbable and that test drilling is attended by more risk of failure than is usually when attempting development of oil even though that mineral is the most elusive elus 1 v e and migratory in of our natural resources |