oil formations in texas.pdf

7/27/2019 Oil formations in Texas.pdf

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O I L - B E A R I N G F O R M A T I O N S I N T E X A S

By J. A. U D D E N , Austin Texas.I shall begin by stating that as I understood it my remarks

should be directed more to the general public than to the professional men who ar e pres ent here. I have followed tha t request,and if the professional men should find some of my remarkscomm onplace I tru st tha t you will excu se me . As I look at it,it is of great importance that we all should have a little understanding of geology, and so to speak, absorb a little of the science.By so doing we will, without really being conscious of it, adjustourselves to the demands upon us in the way of knowing thingsconnected with the geology of petroleum.

No less than 9? per cent of the surface of the State of Texasis covered by sedimentary rocks; rocks that have been depositedin wa ter. If w hen we speak of a formation w e limit the useof this word to sedimentary rocks that have not been greatlyaltered, we can almost say that every formation in the stateis oil-bearing; that is, almost every formation in the state contains at least a minute quantity of material from which oil maybe distilled. T he thickness of sed ime ntary rocks in this statevaries from zero to probably twenty thousand feet, and I presumethat ten thousand feet would not much exceed a fair average forthe thickness of thes e rocks over the entire state. F or an inconceivably long period of time this part of the American contine nt has been in the ma king. Som etimes it has been below thesea, at other times it has been above it. It has never been at rest.These changes of level have been imperceptibly slow. Going backin time as far as the earliest recorded animal life, there must havebeen since then half a dozen submergences, alternating with anequal number of periods during which our land was above sea-level and und ergo ing erosion. T he periods of eme rgence probablylasted just as long as the periods of subm ergence. D uring everyperiod of submergence there was an accumulation of slime, mud,sand and gravel at the bottom of the wate r. All this m ateria l wasderived from lands at oth er places und ergo ing erosion. W ith


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J . A. UDDEN 8every change of currents, in the sea, caused by general and gradual movements of its bed, and of the surface of the land, therewould also be changes in the accum ulating deposits. W he re fora hundred thousand years calcareous slime had been depositingover extensive areas, elevation of the bottom might result in acessation of the deposition of the calcareous slime, and changeto the building up of thick stra ta of mud and clay. By someother geographic change the deposition of clay might ceaseand be followed by a depos ition of sand. A mor e or less wellmarked body of deposits made under more or less identical physical conditions is wh at we call a form ation. Th e grea t numb erand variety of formations is the result of the innumerable slightdifferences in physical and geographic conditions that have prevailed in all ages of the pas t in differe nt pa rts of the sea. Bu tgoing as far back as we know of the past, there is one conditionthat lias always been cons tant. An imals and plan ts have alwaysbeen present in the seas, and their remains have always addedsome thing to the sedimen ts which have been forming. Ev en inthe earliest sedimentary formations that are known, we find evidence of the existence of living things. T he earliest fossils th athave been discovered in the most ancient fossil-bearing rocksshow that life at this stage already was highly organized, andthat it must even then have existed for an immeasurable length oftime.

Plants and animals have apparently in all ages been ableto adjust themselves to the ever-changing conditions of existence,brought on by the physical changes on the earth. Every part ofthe sea is inhabited today. Ev en the Ar tie seas ar e teeming withcertain low forms of life, and the continuity of life from the earliest forms known to those of the present day cannot for a momentbe doubted, though it is evident that at certain periods, conditionsfor life have been more favorable than at others.

The fact that petroleum is the result of a slow distillationof organic material imbeded in the debris that has accumulated in the deposits in the sea is now so well established that itrequires no discussion at this time; and remembering the continuous presence everywhere of living things such as plants and animals, it follows that every formation, at least when it was firstmade, contained some organic material from which oil and gas


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84 O I L B E A R I N G F O R M A T I O N S I N T E X A Smay have been ma de. Te sts made on all kinds of s edime ntaryrocks supp ort this conclusion. Even sandston e tha t originallyformed extensive bars and beaches along the sea coast containsanim al rem ains. Clays, shales and limestones, originally form ingslimes and mud in the more quiet part of the sea, are very rarelydevoid of organic m ateria ls. Th e remains of microscopic organisms and shreds of tissues of larger animals have settled in thesea with the mud of such localities and no doubt were more effectively buried and preserved than organic remains buried inmo re open sands . N o doubt in every age of the pas t by far thegreater amount of organic material underwent decay and destruction and returned to the elements; but considering the slownessof the accumulation, the burial of even a small part of the organic world continuously would result in the preservation of anenormous quantity of organic compounds or their derivatives,in the stratified rocks of the eart h. V ario us estimates on thebitumens thus preserved in practically every formation from whichit has not lately been expelled by heat and pressure, indicates thatif all of this material could he separated from the sedimentaryrocks of the State of Texas, it would be sufficient to form a layerseveral feet thick over its surface.

The oil fields in America, if not all of the oil fields of theworld, may be classified in three groups; fields in which the oiloccurs in strata which have been more or less flexed or folded;fields in which the oil occurs in salt domes; and fields in whichoil occurs in volcanic rod-:. It is also a fact that if we consider thedifferent forms, he different kinds of oil fields we have in theState, there are more forms represented than any other State.

Until three years ago we had not found any oil in commercialquantities in igneous rocks in the Un ited State s. Th e finding ofoil in igneous rocks in the Thrall field was an unusual occurrence . Th is field is, as you kno w, located in the ea stern par t ofW illiamson Co unty. Th is county is unde rlain by sediments ofCretaceous age more than 3,000 feet thick, but it is really not inthese sedimen ts tha t the oil in tins field wa s found. Th e wells ofthe Th rall field go thro ugh the greater part of the Taylo rm arl. On reac hin g the (Uptli of from S00 to 000 feet, most of th eproductive wells ente r an igneous rock. Origin ally this rock wasa basa ltic lava, but it has been changed to a soft and som ew hat


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J . A . T ' D D E X 85porous serpentine and it was this porous rock that contained theoil. Fr om a study of nearly all the well records from this fieldit is evident that the body of this rock underlies something like asqu are mile of territo ry. In one place the rock reaches the thickness of several hu nd red feet. It has the form of a lense convexon the upp er side. Its average thickness in the center of thefield is about 69 feet, and from this point it thins out in three directions to a feather edge. H ow it term inates to the west is notyet determined.

What has happened at Thrall appears to be something liketh i s : During the Cretaceous age most of Texas was part of thesea which extended from Alaska to the Gulf of Mexico. In thissea a thousand feet or more of sediment had been laid-down inthis region during the lower Cretaceous age, and still later another500 feet of chalk and shale had been deposited during the upperCretace ous time s. W he n some 150 feet of marls had been laiddown on these earlier sediments, an eruption occurred on t'-iCbottom of the sea and deposited a low volcanic cone of the dimen sions stated. Sim ilar erup tions took place at the other pointsalong the Balcones Escarpment at about the same time and volcanic dikes and sills were injected into the Cretaceous sedimentsin Travis County, Medina County near Uvalde, and even as farout as in Kinney County. Igneous m aterial belonging to this periodof volcanic activity is nearly all of the same kind. It consists ofvery heavy dark basaltic rock. A fter these erup tions took placesedimentation went on in the sea as before, and extrusions andother material which probably did not reach the bottom of thesea but remained as intrusive in sediments below the bottom of thesea, were all buried under a cover of probably 2,000 feet of marlsand sands in the same ocean.

The marls of the upper Cretaceous formation are quite richin animal rem tins of all kinds, but especially of the small microscopic kind tha t live in th e water at the surface of the sea. Inalmost every pound of marls of these formations there is sufficient organic material today to produce a considerable distillateof oil, if the marl be heated in a ret ort . Th e igneous rock whichbecame imbedded in this marl was subjected to a change that altered its chemical composition, principally by the taking up of agrea t deal of w ater. It is probab le tha t this action resulted in


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86 O I L B E A R I N G F O R M A T I O N S I N T E X A Sfracturing the rock extensively and in mak ing it porous . Afte rthe rock had tihus become porous or while the change was stillgoing on, organic bituminous material crept into it , or was absorbed by it by capillary attraction, from the shales or marlssur rou nd ing it. T he igneous body has later been tilted and itis not impossible that some of the original oil filling the serpentine has been spilled, so to speak, by the tilting of the forma tionholding the oil. A t any rate, the lower part of the rock was foundto be partly filled with water.

It does not seem impossible that other bodies of similarlyplaced extrusives may yet be found and the question has beenasked, what the chances are for finding other oil pools of the samekind. I believe tha t these chances are very small, indeed. Intrusive bodies of the same kind similarly situated can be lookedfor in a belt 10 to 20 miles wide, bordering the Balcones Escarpm ent. It is evident th at no igneous rock can be oil-bearing unlessit be made porous by metam orphic changes. M ost of the volcanicrocks seen in the belt already referred to are not in this condition.

The salt dome fields are as yet but imperfectly understood.In Texas alone it is represented that some thirty-four salt domestructu res have been discovered. A few of these are in the northeast part of the state and have mostly eroded away. W ha tis left appears to be the basal pa rt of these struc ture s. Such arethe Grand Saline and the Brooks Saline. On e large group ofthese structures is distributed over Jefferson, Hardin, Liberty,H arr is , Galveston, Brazoria and M atago rda Counties. A thirdgroup is indicated for San Patricio, Duval, Brooks, and adjacentCou nties. It will be und erstoo l tha t not all of these are oil-producing. M ore than half of them are as yet barre n. But that allof them are essentially of the same kind and that they have beenproducd by the same conditions seems to be quite evident.

The most conspicuous feature of these structures is that theycontain at a gre ate r or less depth , mas sive domes of salt. T hesalt is overlain by gypsum and dolomite that, like the salt, evidently have been introduced or built up in the position they nowoccupy and do not belong in the series of sediments in whichthey now occur. Th ey have been produ ced at a late r day. Itis evident that the salt in these fields has slowly forced its way,or built itself upward, lifting the entire mass of overlying sedi-


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J . A. CDDEX 87m ar t s . T h i s l i f t ing has been so s l ow tha t t he e ros ion of t he su r f ace of t he g ro un d ap pe a r s i n m os t ca ses t o ha ve kep t pace w i ththe s low e levat ion of the land su r fa ce . I t i s only in a few case stha t t he e l eva t i on o f t he g round has exceeded e ros ion and t ha tt he su r f ace o f t he g round ove r t he s a l t domes now has a s l i gh t l yh ighe r e l eva t i on t han t he f l a t su r f ace o f t he su r round ing coun t ry .In t he Sp ind l e T op f i e l d t h i s d i f f e r ence i n e l eva t i on amounted t oonly a few fee t . D am on M ou nd r i ses some TO fee t abo ve thegene ra l l eve l o f t he su r ro un d i ng coas t a l p l ane . B r ya n H e ig h t san d H ig h Is land are o th er ins ta nce s of th i s k ind . In som e of thesa l t dome f i e l ds t he g round wa t e r appea r s t o have d i s so lved t heh ighe r pa r t o f t he s a l t dome and t h i s has r e su l t ed i n a gene ra ls inking of the land as a t Sour Lake .

W ha t has caused t he s l ow accu mu la t i on o f the s a l t und e r g ro un d i n t hese f i el ds i s no t a s ye t kno w n and I sha l l no t a t t e m ptto d i scus s t h i s que s t i on . T h es e f i el ds a r e l imi t ed in ex t en t . T h eoi l is he ld usua l ly in a cap rock whic h over l ies the sa l t . T h e caprock cons i s t s mos t l y o f do lomi t e and i s f r equen t l y coa r se ly c rys ta l l ine an d hig hly po ro us . I t i s f rom the low er pa r t of th i s capr o c k t h a t t h e g r e a t g u s h e r s a r e s u p p l i e d . T h e e n o r m o u s p r o d u c t ion f rom thi s pa r t of the sa l t do m es las t s usu al ly only a fewy e a r s . In severa l of the sa l t do m e oi l f i e lds pr od uc t io n has beenpro longed bv t he f i nd ing o f o i l unde r c l ay fo rma t ions t ha t l apup over the s ides of sa l t do m es , in man )- p laces a t h igh an gles .In the Humble f ie ld r ich minor pools of th i s k ind have beendra ined by we l l s bored a mi l e o r m or e ou t f rom the cen t e r o f t hef ie ld to depths of as much as 4 ,000 fee t .

T h e c o n d i t i o n s u n d e r w h i c h o il h a s b e e n r e ta i n e d u n d e r g r o u n din these f ie lds are in som e sense l ike thos e in o th er f ie lds . T hec lose -g ra ined c l avs and mar l s and t he t i gh t uppe r pa r t o f t he caprock have p rev en t ed t he oil f rom com ing t o t he su r i a ce and t h usescap ing . T he ove rhang c l ays and t he cap rock fo rm inve r t ed bas in in which the oi l i s he ld by the upward pressure of the groundwate r . No spec ia l exp l ana t i o n o f t hese cond i t i ons is nece s sa ry .I t ap pe ars tha t the coas ta l sa l t do m e f ie lds exis t in d i f f ere nt s tagesof deve lopment and pe r f ec t i on . T he sa l t domes o f t he s a l i nes maybe r ega rded a s s t ruc tu res t ha t have been no t on ly made , bu t a l sop a r t l y d e s t r o y e d . T h e D a m o n M o u n d is a s a lt d o m e w h e r e th ecap rock has deve loped an unusua l t h i ckness and has been pushed


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SS O I L B L A R I N G F O R M A T I O N S I N T E X A Sup above the general level of the coastal plain. Th e usual depthat which the cap rock lies below the >urface of the ground in mostof the fields is per hap s abou t 1,000 feet. In the Goose Creekfield the cap rock is as yet not as well developed as in some of theoth er fields of this kin d. H er e it lies at a dep th of 3,500 feet. Ithas been suggested that the great depth to the cap rock in thisfield is due to the fact that the salt dome in this case is in anincipient stage of formation . Th e Goose Creek field would thenrepresent the early stage in the formation of a salt dome structure, and the Damon Mound would represent a very late stage.

While the salt dome oil fields are like other oil fields in thatthe oil is held in a porous body by an impervious rock, the conditions which ob tain in the coastal oil fields ar e entirely diffe rentfrom those existing in most other fields in all parts of the world.Th e salt domes are relatively very high and narr ow . The ir horizontal exten t is small. Some of them approx imate the proportions of a tree stump rounded at the top and appear as if tliey hadbeen pushed up throu gh the strata like a huge punch . Th e str atathat have been penetrated are pushed aside and more or less torn,as it were.

The rock that contains the oil on the top of the salt domehas not been found anywhere except in the dome structures. Itcannot be classified with any of the strata in the formationspenetrated by the dome and it would not at all be surprising, if,when we know more about the history of the salt domes, weshould find that the bedrock in different salt domes is made atdifferent times. You will unde rstand then that we cannot in thecase of the salt dome structures, speak of the oil-bearing rock as aformation of the Tertiary sediments in which it lies.

You will see from this account of the oil fields of the coastthe reason, I think, why geologists have been able to do so littletow ard th e finding of these fields. F or the mo st par t, the coastis superficially covered by recent deposits that have been but littleaffected by the local disturb ance s by the salt dom es. The se deposits are of soft sands and clays in which any folding that mayexist is entirely concealed superficially. A geologist cannot, asin most other fields, make out the dips of the formations throughwhich the salt domes hav e been raised. N atu rally many of thecoastal dome fields have been discovered by accident.


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J . A. UDDEN 89Those who have given most attention to the development of

the oil resources in this part of our state look, nevertheless, uponcertain physical characteristics as somewhat diagnostic of aburied salt dome . Th e most conspicuous of these "surface conditions/' as we call them, is the existence of a tract of elevated.land having a very flat dome-like shape. Th is, as I have alreadyexplained, is the topographic expression of a salt dome where thedom e is raised faste r tha n it can be eroded aw ay. An othe r is theexistence of depressions in the surface of the plain, resulting, asit is believed, from solution of the salt causing a settling ofthe overlying land. A no the r surfac e indication is the continuousescape from the gro un d of gas and oil. Th ere can be no doubtthat oil and gas escape to the surface slowly from some of the oilpools in these stru ctu res . Some believe tha t such escape of gashas resulted in places in the formation of small hillocks in theplaces wh ere gas has escaped for a long time. Spring s of waterof unusual temperature and of unusual mineral qualities are alsobelieved to issue from some of the salt domes, the supposition being that these are really artesian waters coming from the mineralized grou nd close to the cap rock. Still ano ther su rface indicationis the presence in the soil of a material called "para ffin dirt ."This is not at all paraffin, but more resembles a precipitate ofpeaty material, if such a substance may be supposed to ever benroduced by na tur e. W he n heated +his substance gives an odor"f peat. It resem bles art gum in its colo r and physica l appenr.-mrr.-hen it contains the moisture usually present in the subsoil


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90 ' i n . U K A I U N G F O R M A T I O N S I N T F N A S

fo r f i nd ing o th e r o il f i el ds w i th a s poo r ly m ark ed su r f ace i nd i ca t ions as the Goose Creek, in many other p laces , f roan the RioG ra nd e no r th w ar d. I t seems l ike ly tha t o i l f i e lds wil l be di s cove red i n o the r p l aces where t he re a r e i nd i s t i nc t domes .

Nine- tenths of a l l the oi l f i e lds of the wor ld be long to thek ind I have men t ioned a s ho ld ing o i l i n s t r a t a which have beenm or e r l ess f lexed o r fo lded the th i rd gr ou p of o i l f i e lds th a tI en um era t ed a t t he beg inn ing . E x ce p t i n g t he T hra l l f ie ldand our coas ta l f i e lds in th i s Sta te and in Louis iana; a l l the oi lf ie lds in the Un i ted St a te s , so far kno w n, ma y, 1 th in k, be c lass i fied he re . In co m ing to an un de rs ta nd in g of o i l pools of th i skin d i t is well for us to again reca l l the fact th at n ea rly al l ou rfo rma t ions a r e ve ry , ve ry o ld ; t ha t i n t he cour se o f t ime t he ea r t hhas never been a t res t ; tha t i t has for long per iods been l i f t ed here .sun k the re , fo lded in som e places an d fau l ted a t o th ers . Mo stsands and c l ays were l a i d down f l a t and were o r i g ina l l y hor i zonta l . Bu t such i s no t th e i r pos i t ion toda y and the t ime s ince theyw ere di s turb ed in the i r pos i t ion m a} ' lie so far back tha t who lec o n t i n e n t s a n d m a n y m o u n t a i n r a n g e s m a y h a v e b e e n m a d e f r o mthe ear th s ince tha t t ime, and very l ike ly as man} ' o i l -bear ingfo rma t ions a s now ex i s t mav have been e roded and washed awayf rom the con t i nen t s s eve ra l t imes . U nd er s t an d in g t h i s , we a r epre pa red t o app rec i a t e t he g r ea t nu m be r o f d i f f e r e n t k inds ols t ruc tu res i n which o i l may a t p r e sen t be en t r apped be low thesur f ac e of the g ro un d i n such fo rm a t ion s . I need on ly r e f e r t osome . T h e mo s t com mo n pe rha ps is t he an t i c l i n e : t ha t is . anup w ar d fold . Th is m a} ' be high or low, the rock s r i s ing f rom lessthan ten to more than a thousand fee t in a mi le on e i ther s ide tow ar d the cres t of the s t ru c tu re . Oi l wi l l t rav el tow ard the high es thumps o f t he an t i c l i ne and may be absen t i n t he l ower p l aces .INTost of the oil f ie lds in Pe nn sy lva ni an m ay be ascr ib ed to s t ru ctur es of th i s l and , M an v occu r in the cen t ra l and we s tern Sta tes .Do me - l i ke s t ru c tu res a r e a l so kn ow n. In one sense dome s a r eme relv shor te ned a nt ic l in es . Th ey can ha rd ly be sa id to be as f requ en t a s an t i c l i nes , ho we ver . S t ruc tu r a l t e r r ac es is an o th e r c l a s s .W e have he re a s t ru c tu re wh ere rocks , a f t e r r un n in g up on adip or s lope, wil l l ie f lat fo r som e dista nc e, an d ma}- the n co ntin ueto dip as befo re . Tn suc h a f la t s t r uc tu re o i l i s apt to acc um ula tet inde r the -he l f - l ike level pa r t of the form at io ns . Yo u wi ll pe r -


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J . A . UDDEN 9 1ceive that a structure of this kind does not give as good promiseas an anticline or dome, for the reason that at one side of the levelstru ctu re the re is no retaining limb. Th e oil may have escapedby that route.

An othe r favorable struc ture is an edge sand. W her e theformations dip for many miles in one and the same direction,there is little prospect for oil being found, as it may travel alongthe un der side of the retaining formation and may escape to thesurfac e. W e hea rd in the discussions this forenoon that we havesuch a condition over the region where we have our best stratafor oil fields, but if this represents sand, a sandy layer, and ifthese papers represent the clay, then we have a condition that wem ay call edged sand. (Illus tratin g with pape rs.) But if insuch a structure there should be found a sand which would terminate upward between two clays, it is clear that any oil in thissand would be retained, unless there w rere some lateral escapein one direction.

In the old mountain structures of the Appalachians, faultshave always been avoided by prospectors, and' for good reasons.The oil seems to have escaped through the faults, which haveacted as open fissures. The Appalachians, as you will remember,are relatively very old mountains, and it is quite likely that although no oil is found in reservoirs that terminate against faultsin the Appalachian country at present, by faults we mean placeswhere the ground has been fractured and the rocks moved up anddown, it may very well be that at some earlier date the oil wasstill ther e. A t any rate, it has been found in California tha tsands cut by faults are sometimes good reservoirs for retainingoil. It may be th at the faults in California y et retain th e oil onaccount of their youth . Th ere is not the slightest doubt thatthe faults in the Appalachian mountains are, as a rule, twenty orthirty times as old as the faults in the coast range in California.Ano ther exp lanation ha s, how ever, been made for this difference.It has been shown that the heavy residue in certain oils in California is effective in sealing up the faults.

The various kinds of structures capable of retaining oil aretoo num erous to be fully discussed in a brief prese ntation. Th equestion in which we are especially interested is, what strata contain oil in the sediments in Texas Perhaps I should mention for


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92 O I L B E A R I N G F O R M A T I O N S I X T E X A S

the benefit of some of you that we distinguish between older andlater rocks that have been made during the past history of the earthand we speak of the very oldest rocks as the crystalline rockstha t unde rlie everythin g else, and then we have a series of formations one above the other, of sedim entary rocks. In enume ratingthe oil bearing formations of Texas I shall begin by mentioningthe lowest, the oldest of these rocks. Th e oldest rocks in whichwe know of any oil in this state is the Ordov ician. In an upliftwhich covers n re of the size of an average county in the vicinity of Marathon, in Brewster County, these rocks are presentover some hun dred sq uare miles. Th eir condition is here unlikethat in the central pa rt of the state. The y have not been metamo rphose d into ma rble, they are still highly bitum inous. It isbelieved that a well which was bored to the depth of about athousand feet some years ago obtained a little oil from these Or-dovican rocks. Th e Silurian and the Devonian rocks are practically abse nt from this state. It is doubtful if we have anyMississippian in Texas.

A formation known as the Bend, named from the Bendpostoffice in San Saba County, was described some twenty yearsago by Dr. Cummins, whom we have had the pleasure of listeningto today. I guess it was nearly thirty years ago when they weredescribed. U p to this tim e w e lack positive proof t ha t the formation is Mississippian. I today spoke to Dr . M oore, from K ansas, who has made quite a study of our fauna of these rocks, and 1understood that he is of the same opinion as Professor Cummins,that they 'belo ng to the Pennsylvanian age. This is known to liealso on the south side of the uplifted area in Llano and BurnetCounties, and it outcrops in the vicinity of Marble Falls.

This formation dips under the Pennsylvanian to the northand does no t rise to the surface again in this state. Th ere can beno doubt that it is continued somewhere under the counties ofBrown, East land, Palo Pinto , Jack and Montague, up into Oklahoma, and lies within reach under other counties to the east andwe st of this line. Th is form ation consists largely of blacklimestone and black shales and it contains some sands also. T hewhole is strongly bituminou s. Th e basal shale in this formationis seen in San Saba County where it contains a large amount ofbitum inous mate rial. Un til recently it has generally been sup-


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J . A. UDDEN 93posed tha t the B end lay too deep for success fnl explo ration bythe drill, but during the last two years some borings have beensunk into this formation in Eastland, Stephens, Palo Pinto andother counties, and some highly productive deep oil-bearing sandsare now being developed in this formation.

Later rocks of undoubtable Pennsylvanian age underlie aquadrangular area extending from Montague to Lampasas Countyon the east and from Concho to W ichita Co unty on the west. Itis tru e that these rock s do not come to the surfac e over thisentire area. On the east they are covered by the Com anchean -Creta ceous and on the west by the Perm ian. But they lie atdepths suitable for exploration in a rectangular area some 100miles wide and some 240 miles long from north to south. In thisregion we have the same formations that have yielded most of theoil in Ok lahom a and K ans as. W ha t are the chances of findingoil in these stra ta in this state? Alre ady we have several fieldsdevelopedat Electra, at Petrolia, near Moran, and near Strawn,with scattered prospects where smaller quantities of oil or gashave been found, in single wells or in several wells, as at Trick-ham, Mineral Wells, Bangs, Lohn, Santa Anna, and Abilene, andI have no- doubt left ou t some. It may he true tha t our P ennsy lvanian contains less sands than the Pennsylvanian of our neighbor state to the north. Espec ially as we go west do the sands toneswhich lie in reach of the drill appear to grow smaller and lessfrequent. Bu t certainly our Penn sylvan ian contains a sufficientnumb er of san dy beds to store a vast quan tity of oil. Look ingat the structures which are developed in the area and the bedsunder consideration we find that the general position of the stratain this region is very much like that farther north in Oklahomaand Kan sas. Th e beds have a general dip to the west over mostof the region defined. Possibly this general dip is somew hatgreater in Te xas than further north . In the southernhalf of the area the average dip seems to be near 30feet to the mile, being pro bably greatest farth eres t southowing to the uplifts in the Ce ntral Min eral Reg ion. You willund erstan d from this that p rovided th ere are sands in thePen nsylvan ian which term inate in shales to the ea stw ard,there are good chances for oil and gas pools in edge sands. Itwould be very singular, indeed, if no considerable pools of this


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94 O IL , B E A R I N G F O R M A T I O N S I N T E X A Skind were found over so large an area. Th e region has not beensubjected to any grea t disturbances. Th e formations as a ruleare folded only with extrem e gentleness. Th ere are many placesWhere struc tural terrace s exist. Dips to the east in a region ofgeneral monoclinal structure to the west will give the right anticlinal struc ture and all such struc tures should be tested. Go odexposures of the bed rock occur over most of this region and byprope r careful exam ination of these expos ures some favorablestructures have already been found by the two or three hundredgeologists who ha ve been at work in this state. I wish to pay myrespects to the persistent and successful work that you have done.T his is a region w here geological wo rk can be expected to be effective, and no test should be made without the advise of a geologist. Th e sands of the Cisco and Canyon have already yieldeda great deal of oil in the Electra field and some of the sands of theStrawn formation have proved oil-bear ing near Strawn and Mo-ran. Fr om some studies which we have recently made in thewestern part of the state it is probable that some unconformitiesexist in the Pennsylvanian in the central part of the state, as wellas in the west. Fr om some observations that we have mad e, itdoes not seem so unlikely that the unconformities will separatethe Permian from the Pennsylvanian, but rather that we willfind some unconformities in the Pennsylvanian itself and in thePermian, for such are the conditions in the western part of thestate. Th is is a feature w hich m ay ma ke the work of field geologists looking for oil, excep tionally difficult. It appears likelythat there may be not only one, but possibly two or three unconformities. It seems quite probable that there is an uncon formitybetween the Pennsylvanian and the Permian, and it is quite likelyalso that other unconform ities may exist. Th e work necessary tosolve these structural problems requires not only considerabletime in the field, but the most intimate knowledge of fossil forms.The studying of fossils is a work to which oil geologists can givebut little time, and it is for that reason, the special function ofofficial surveys maintained by the state and national governme nts. I regret very much tha t so little has been done in the w ayof w ork ing u p the fa una , th e fossils o


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J . A. UDDBX 95lower part of these rocks included in the formations known asthe Albany, the Wichita, the Clear Creek, and the Double Mountain consist of shales, limestones, and some sandstones. Nea rlyeverywhere the limestones are bituminous, especially in the lowerformations. Th ere seems, howev er, to be a dearth of porousrocks capable of serving as reservo irs. I was very much impressed with this fact in the study of sections of the Glass Mountains. Going farther and farther west the sandstones play outand the shales are replaced by limestones, frequently changed todolomites. W est of the Pecos, limestones are predom inent inthe Perm ian. Th e numb er of explorat ions that have been mad ein the formations of this age is not as yet very great, and fewif any, of the m have been scientifically located. F o r tha t reasonI do not consider the negative force of that evidence as conclusive as it would be otherwise.

Finally, we must not entirely overlook that large area betweenthe Llano and the Marathon uplifts, where the Pennsylvanian andthe Per m ian rock s with out any doubt, underlie a cover of from100 to 1,000 feet, or m ore , of Com anche an limeston es. Th is hasbeen called the Edwards Plateau, the great limestone country ofthe southewestern part of Texas. I fully believe that some oilfields will be found on this Plateau. That some structures favorable for the collection of oil in the Pennsylvanian and the Permiansediments underlie this area there can be no doubt. W e knowthat the M arat hon uplift extend s north eas twa rd beyond its exp osures and there can be no doubt that the Lla no uplift had bro ughtup the Pennsylvanain rocks to the surface westward and southwa rd before the adva nce of the Comanchean Sea. This regionshould be hand led carefully. Pos sibly it m ay be of some interestto geologists to mention that there the Comanchean sedimentshave lately been uncovered, the present drainage is consequentto the larger structures; which suggests that anticlinal folds maycoincide with the present divides in the drainage.

Leav ing the formations of the Paleozoic age we findtha t these are separated in Texa s by a great unconfo rmity fromthe overlaying Mesozoic formations. In other words, we findthat after the Pennsylvanian and Permian had been laid downin the Paleozoic seas, and the greater part of this state waslifted above the waters of the ocean and for a long period sub-


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96 O I L B E A R I N G F O R M A T I O N S I N T E X A Smitted to extensive erosion. As I have already stated in connection with the description of the Thrall field, the entire statewas again submeregd at the beginning of the Comanchean period. D urin g this period deposits consisting chiefly of limestoneswere laid down with a thickness of from perhaps only a few hundred feet, in the northern part of the state, to at least two thousandfeet near the Mexican border. The Comanchean limestones are in-terbedded with some m arls. W ith a single exception, this wholesystem of rock has so far proved to be barren of oil and gas, theonly exception being a small field in the I'aluxy sands of theSou th Bosque, west of W aco . At this place the re are somewells from 400 to 500 feet in depth, that yield from ten to twentybarrels of oil per day, or that was the condition when I was inthe place about two years ago.

The upper Cretaceous is of a different kind of material.It consists in the main of marls, marly limestones and bituminousclays. Th e principal oil-bearing horizons in the uppe r Cretaceous are those from which production has been obtained atCorsicana, Powell, Mexia, and in the Caddo Lake region in thenort hea stern p art of the state. At Corsican a there is a sand inthe lower part of the Taylor marl from which production hasbeen obtained for the last twen ty years . Th e oil present in thissand is seldom more than a few feet deep, and many a well hasbeen tost by going too deep into the salt water below the oil. Thelowest oil-producing sand in the upper Cretaceous is known asthe Woodbine sand. This forms the base of the formation, and itappears to be of about the same age as the Dakota sandstonein the northern part of the United States and Canada, where italso has been found t o yield some oil. Th is is th e sand whichgives the lower oil in Marion Count}', in the Caddo Field. Theformation is known to underlie the country of northeastern Texas over probably some twentv or thirty counties in a regionwhere the general structure is almost horizontal and where forthis reason it would see'm that conditions for the retention ofpools wou ld be likely to occur. It seems to me tha t this sandhas not received the attention from geologists which it shouldhave. One reason for th is, perh aps , is that it lies deep in theeastern par t of the state. Th e irregu larity of the sand is likelyalso to make nec essary ve ry careful testing of an}' holes to be


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J . A. UDDEX 97ma de. One of the encouraging features of the prospectingof this sand lies in the fact that it is known to be affected by abroad uplift extending in a northwest-southeast direction fromPano la to Grayson County. A discouraging feature is the factthat the rocks exposed at the surface do not always representthe deeper structures as in the case where the Cretaceous rocksare overlain by the Tertiary; and the further fact that in this entire region exposures are few and give but little guidance to thegeologist in ma king out local stru ctu res . You will perceive tha twhat has been said with regard to the Cretaceous sands in thenortheastern part of the state will be true also for a belt extending toward the south and west, following the western boundary of the Terti ary sedim ents. It may be interesting to notethat this belt terminates in Texas in the southern part of Maverick County and that at a point about 22 miles southeast of EaglePas s two gas wells have been made. In both the gas was foundin some sands higher up in the upper Cretaceous formation thaneither the Eagle Ford or the Woodbine.

I should, perh aps , say a few word s with rega rd to thechances of finding oil or gas in the Eoc ene Te rtia ry . Th is formation extends in a belt from Louisiana to Mexico, southeast ofthe Cretaceous area. Th e Te rtiary taken together has a thickness of not less tha n 4,000 feet. It consists of marls and sand sand it contains at least two horizons in which lignite beds arefrequently found. O ve r this entire are a gas and oil have beenobserved escaping in a great number of springs and in shallowwells, but so far not a single large oil field has been discovered.The formation as a whole contains considerable bituminous material and there are some geologists who still hope that oil poolsma y yet be found in the deposits of this age. O ur experien ceso far has been discouraging, except in localities where salt domesexist, as I have already explained. Th e general structu re is a dipto the southeast. On e o f the reasons why oil may not have accumulated to a greater extent than has yet been found in this formation is its steep dip, which in many places amounts to as much as50 feet per mile. If th is is th e cause of the scarcity of oil in th eEocen e Te rtia ry, it would seem tha t the best chances for findingany pools that may exist is in northeast Texas and in the RioGrande embayment from Three Rivers to Carrizo Springs.


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'S i M L H K A K I X G F O R M A T I O N S I X T K X A SVery l i t t l e prospect ing for o i l or gas has so far been un

der taken in tha t par t of the s ta te which l i es wes t of the PecosRiv er . .Most of th i s co un t ry has no lack of fav ora ble s t ru c tu res .In t he o lde r s t ruc tu res which a f f ec t t he Pa l eozo i c rocks i n t h i sr eg ion i t i s qu i t e dou b t fu l t h a t any cons ide ra b l e b i t um inou sdepos i t s w il l be d i scove red . Sh a r p fo lds and f au l ts which ha vebeen in exis tence s ince the end of the Paleozoic era can notbe r eg a rd ed a s p rom is ing . ISu t t he re a r e s t ru c tu res in o the rp l aces which have been made s i nce t he t ime t he uppe r Cre t a ceous was la i d dow n and t hese m us t be con s ide red a s so m ew ha tm o r e f av o r a b l e . T h e a r e a s w h e r e t h e u p p e r C r e t a c e o u s d e p o s i t ss ti ll r em a in a r e qu i t e l imi t ed . T h ey p robab ly do no t exceed tw enty tho us an d sq ua re mi le s . I t m ay be of in te res t to s ta te tha tsome gas was d i scove red more t han t h i r t y yea r s ago i n t he uppe rCre t ace ou s in t he \ i e j o Va l l ey so u th o f V a l en t i ne .

In conc lus ion l e t me say t ha t I have found i t imprac t i cab l eon th i s occas ion to present more than the meres t out l ine of the oi lgeo logy o f t he s t a t e o f T e xa s . O u r fo r m a t io ns a r e man y andva r i ab l e . T he a r ea o f t he s t a l e i s l a rge and geo log ic s t ruc tu re i scom plex . A l l t ha t \ have a t t emp ted t o p r e s en t t o you is a f evof the genera l ideas wh ich ma} ' he lp to ac qu i re the r igh t po intof v iew in approaching the subjec t of the geologic s tudy of cnland gas . I n t he de t a i l ed kno wled ge of our fo rm a t ion s we a r efar behind in the s ta te , owing a t l eas t in par t to the fac t tha t thework p rov ided fo r by t he s t a t e has been d i scon t i nuous and i n t e r r up t ed . I t is my hope t ha t t he bu rea u I r ep rese n t sha ll be i na pos i t i o n t o un de r t ak e such gene ra l work a s is need ed fo r ac c u r a t e d e t e r m i n a t i o n o f i m p o r t a n t s t r a t i g r a p h i c h o r i z o n s , i i " ton lv by t he pa l eon to log i ca l me thod f rom the s t udy o f fos s i l s ,bu t a l so i n t he s t udy o f un de rg ro un d cond i t i ons f rom we l l r e cord s . and f rom the ex am ina t i on o f cu t t i ng s s ecured f rom dr i l lho l e s . I n t h i s l a s t k ind o f w or k m uch m ore mig h t be done , andshou ld be done , whi l e p rospec t i ng i s gene ra l , and whi l e obse rva t i ons can be m ad e on the va r i ou s fo rm a t io ns wdii ch a r e be ingexp lo red .

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