fracture analysis and mapping of the cretaceous boquillas ...• fracture analysis of the boquillas...

FractureanalysisandmappingoftheCretaceousBoquillasFormation,BlackGapWildlife

ManagementArea,BrewsterCounty,TXWilliams,J.W.,Alsleben,H.,andEnderlin,M.B.

SchoolofGeology,Energy,andtheEnvironment,TexasChristianUniversity,FortWorth,TX76129

• StratigraphicunitsalongwithprominenttopographicfeatureslocatednearHeathCanyonmayrePlectthestressesoftwomajordeformationalepisodes:Laramide-related

shorteningandBasinandRangeextension.ShorteningstressesduringtheLaramideOrogenyproducedtheSierradelCarmenMountains,thehighpeakswithinalongthe

westernborderoBlackGapWMA.Thelocationofthestudyareamaybeanorth-easternextensionofthismountainrange.BasinandRangeextensionalstressesgenerated

high-anglenormalfaultsandhalf-grabenstructureswhichjuxtaposeSantaElenaLimestoneagainsttheyoungerBudaLimestoneandBoquillasFormation.Thesefaultsare

consistentwithBasinandRange-relatedhigh-anglenormalfaultswithinBigBendNationalPark.Additionally,asaresultofthisfaulting,stratigraphicunitswithinthearea

aretilted~10-15°tothesouthwest.

• FractureanalysisoftheBoquillasFormationwithinHeathCanyonrevealsaconjugatesetoffractures.Set1hasanaveragestrike/dipof223°/63°.Set2hasanaverage

strikeanddipof53°/75°.Paleostressdirectionsmaybeinferredasroughlynortheast/southwestbasedontheaveragestrikeofthesefracturesetswhichisconsistentwith

thepaleostressdirectionsassociatedwithLaramidedeformation.

• PreviousstudiesshowalinearrelationshipbetweenmodeIfracturespacingandbedthickness.Datainthisstudyshowanon-lineartrendbetweenthesetwovariables

whichsuggeststhattheBoquillasFormationfracturesdifferentlythantheformationsanalyzedinpreviousstudies,thefracturesseeninthisstudyarenotmodeIfractures,

orthattheclassiPicationoflayeringforthisstudywasincorrect.

• Lithologymayplayaroleintheverticalpersistenceoffractures.XRFanalysisallowsthecarbonaterocklayersoftheBoquillasFormationtobeclassiPiedintoeithercalcite

dominantlimestonesorcalcite-claydominantmarls.Thesetwochemicallydistinctrockstypesexhibitdifferingrockstrengthvalues.Limestonelayersgenerallyhavehigher

strengthvaluesthanmarllayers,afunctionofhighercalciteandlowerclaycontent.Duetothestrength,limestonesbehaveinamorebrittlemannerthanmarlsallowing

fracturestopropagatemorereadily.

• Thoughpreviousstudiessuggestthenatureofbed-to-bedtransitions,gradationalorabrupt,affecttheverticalpersistenceoffractures.dataproducedinthisstudyshow

littledifferenceinthefrequencyofthrough-goingfractureswhenthelayerinterfaceisgradualorabruptwithinlimestone-to-marltransitions.However,whentheinterface

iscomposedofthinashbeds,thereisamarkeddecreaseinthefrequencyofthrough-goingfractures.

Abstract Data

Background

Analysis

Conclusions

Figure3:BrükerTracerIII-Venergy-dispersivex-rayPluorescence(ED-XRF)spectrometer(ImagefromBruker

2015).

Figure1:EquotipBambino2micro-reboundhammermetalhardnesstester(ImagefromProceq).

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Sources: Esri, HERE, DeLorme, Intermap, increment P Corp., GEBCO, USGS, FAO,NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, EsriChina (Hong Kong), swisstopo, MapmyIndia, © OpenStreetMap contributors, and theGIS User Community

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±

LegendLinestype

Contact³ Fault

³ ³ Fault Inferred

Kse

Kbu

Kb

Qg

Qal0 0.45 0.9 1.35 1.80.225

km

A

A’

TheEagleFordShaleinsouthTexasisoneofthemostproliPicunconventionalhydrocarbonplaysintheworld(Breyer,2016).).

In2015,naturalgasandoilfromthisPieldhitpeakproductionnumbersat5,539MMcf(millioncubicfeet)and1,118,648Bbl

(barrels)perday,respectively(TexasRRC,2016).InSeptemberof2016,theEagleFordShaleproduced1,027,000Bblperday,

approximately23%ofunconventionaloilproducedintheUnitedStatesforthatmonth(EIA,2016).Inorderforthislow-

permeabilityformationtoproduce,companiesareusinghydraulicfracturing,astimulationtreatmentusedinlow-permeabilityrock

wherebyPluidsarepumpedathighpressuresintoreservoirs,causingnewfracturestoopenand/orthereactivationofexisting

fractures(Schlumberger,2016).

Theaimofthisstudyistoidentifyanygeomechanicalandgeochemicalpropertiesthatoptimizefractureconnectivitywithinthe

BoquillasFormation,theWestTexasEagleFordShaleequivalent.TheBoquillasFormationiscomposedofalternatingbedsof

calcareousshale,marlandlimestone,rocktypesdePinedbytheircalcite,clay,andsilicacontent.

Herewepresentageologicmapcompletedat1:6000scaleoftheareainandaroundHeathCanyonaswellasdatatakenfrom

fouroutcropstationswithinHeathCanyon.Mappingwascompletedtounderstandlocaldeformation.Fracturespacing,frequency,

andverticalpersistencemeasurementsweretakeninthePieldaswellasrockstrengthandhardnessmeasurements.Rockstrength

wasmeasuredusingtheEquotipBambino2(Fig.1)androckhardnesswasdeterminedusingapointloadpenetrometer(dimpler)

(Fig.2).Energy-dispersivex-rayPluorescence(ED-XRF)datadeterminedthebulkelementalcompositionofthematerialandsemi-

quantitativelyassesschemicalvariationsthroughouttheoutcrop.ED-XRFanalyseswerecompletedusingaBrukerTracerIII-V

spectrometer(Fig.3).ED-XRFandstrength/hardnessdatafromthisstudysuggeststhatfracturefrequencyandlengthareaffected

bytheclayandcalciumcarbonatecontent,and,byinference,thestrengthoftherock.

Figure2:Pointloadpenetrometer(dimpler)modeofoperation(top)andgraphshowingthe

relationshipbetween“tick”marksandunconPined

compressivestrength.

Figure8:(left)Geologicmap

(1:6000)ofthe

areainand

aroundHeath

Canyon,Black

GapWildlife

Management

Area.

BlackGapWildlifeManagementArea(WMA)encompassesapproximately

103,000acres(160mi2)(414km2)withintheTrans-Pecosregionofwest

Texas(Fig.1).TheTrans-PecosisboundedbythePecosRivertotheeast,the

thirty-secondparalleltothenorth,andbytheRioGrandeRivertothesouth

andwest.ThewildlifemanagementareaiseastofBigBendNationalPark.

BlackGapWMAisapartoftheChihuahuadesertbiomeandisunderthe

managementofTexasParksandWildlife.

TheTrans-PecosregionofTexashasexperiencedmultiplemajor

deformationalepisodesincluding:(1)LatePaleozoicshorteningassociated

withtheOuachitaorogeny,(2)CretaceoustoTertiaryLaramideshortening

andtranspressionaldeformation,and(3)TertiaryBasinandRangeextension

(MuehlbergerandDickerson,1989;Maxwelletal.,1967;St.John,1966)(Fig.

5).TheTrans-Pecosalsoexperiencedwidespreadmagmatismfromthe

MesozoicthroughtheCenozoicrelatedtotheLaramideorogenyandBasin

andRangeextension(Turneret.al.,2011).

TherockunitswithinBlackGapWMAareCretaceousoryounger.The

LateCretaceousmarinerocksweredepositedoncarbonateplatforms

northeastoftheChihuahuaTrough,whichformedduringlateTriassicrifting

associatedwiththeopeningoftheGulfofMexico(Fig.6).Thisriftbasinwas

locatedeast-northeastofasubductionrelatedmagmaticarc,whichwasthe

sourceforLateCretaceousclasticsedimentsintheTrans-Pecos(Lehmanand

Busbey,2007).The

carbonateplatforms

thatdevelopedinthe

EarlyCretaceouswere

thesiteofdeposition

fortheSantaElena

Limestone,theBuda

Limestone,andthe

BoquillasFormation,

whicharethe

dominantunitsinthe

studyarea(Fig.7).

Asidefrombeing

widespreadinthe

studyarea,rocksthat

make-uptheCoahuila

Platformunderliethe

majorityoftheTrans-

Pecosregion(Lehman

andBusbey,2007).

Figure7:StratigraphicColumnoftheBigBendarea(ModiPiedfromTiedemann,2010).

Figure5:MajortectonicepisodeswithinTrans-PecosTexas(fromMuehlbergerandDickinson,1989).

A

B

C

D

Figure10A-D:Outcropstations1-4(A-Drespectively)photosandlinedrawings

withassociateddatatablesbelow(photos

donothavetheresolutiontoincludeall

fracturesinlinedrawings).

Figure11A-D:Stereonetdataofbeddingplanesforoutcropstations1-4(A-D

respectively).

Figure12A-D:Stereonetdataoffracturesforoutcropstations1-4(A-D

respectively).

Figure13A&B:XRFdataforallbedswithineachoutcropstation(A).The

averagecalicite-quartz-claycontentof

eachsample.(LS=limestone)(B).

A

B

Breyer,J.A.2016,Introduction,inAAPGMemoir110:TheEagleFordShale:ArenaissanceinU.S.oilproduction,pp.259-283.

Brüker2015,Tracerseriesoverview.Accessed:April6,2015.https://www.bruker.com/products/x-ray-diffraction-and-elemental-analysis/handheld-xrf/tracer-iii/overview.html

Lehman,T.M.,andBusbey,A.B.,2007,SocietyofVertebratePaleontologyFall2007BigBendFieldTripGuidebook,Austin,SocietyofVertebratePaleontology.

Muehlberger,W.R.,andDickerson,P.W.1989,StructureandstratigraphyofTrans-PecosTexas:ElPasotoGuadalupeMountainsandBigBendGuidebook,20-29July.Washington,D.C.:AmericanGeophysicalUnion.

Maxwell,R.A.,Lonsdale,J.T.,Hazzard,R.T.andWilson,J.A.1967,GeologyofBigBendNationalPark,BrewsterCounty,Texas.UniversityofTexasatAustin,BureauofEconomicGeology,TexasUniv.Pub.6711.

Proceq.EquotipBambino2ProceqMetalHardnesTesters.LastmodiPiedOctober17,2016.AccessedOctober17,2016.http://www.proceq.com/jp/nondestructivetestequipment/metal-testing/hardness-testing/equotip-

bambino-2.html

RailroadCommissionofTexas(TexasRRC)2016,EagleFordShaleinformation.LastmodiPied:April5.AccessedApril13,2016.http://www.rrc.state.tx.us/oil-gas/major-oil-gas-formations/eagle-ford-shale/

St.John,B.1966,GeologyofBlackGapArea,BrewserCounty,Texas.geologicalquadranglemapGQ-0030BureauofEconomicGeology,vol.18,UniversityofTexasatAustin(1966)geologicmapscale:1:62,500

Tiedemann,N.S.2010,ThesequencestratigraphyoftheCommanchean-GulPianinterval,BigBendNationalPark,WestTexas.[Master’sthesis]BallStateUniversity.

Turner,K.J.,Berry,M.E.,Page,W.R.,Lehman,T.M.,Bohannon,R.G.,Scott,R.B.,Miggins,D.P.,Budahn,J.R.,Cooper,R.W.,andDrenth,B.J.,2011,GeologicmapofBigBendNationalPark,Texas:USDepartmentoftheInterior,US

GeologicalSurvey.

U.S.EnergyInformationAdministration(EIA)2016,Drillingproductivityreport.LastmodiPiedSeptember12.AccessedOctober25,2016http://www.eia.go/petroleum/drilling/archive/2016/09

References

Figure14A,B,&C:Cross-plotsofUCS(psi)(bambinoinblue&dimplerinred)vsXRFdataforallbedswithineachoutcropstation.

UCSvs.calcite(%Ca)showsapositivecorrelation(A).UCSvs.quartz

(%Si)showsnotrend(B),whereasUCSvsclay(%Al)showsa

negativecorrelation(C).

A

B

C

Figure9:(right)Locationofthe

fouroutcrop

stationswithin

HeathCanyon.

Figure 16: Stereonet displaying the orientation of both sets of fractures with inferred paleostress directions.

• Highanglenormalfaultsassociatedwith

TertiaryBasinandRangeextensionare

responsibleforthepresentdaytopography

withinthemappingarea.Thedeformation

associatedwithBasinandRangeextension

causedthetiltingofgeologicunitsaswellas

forminghalf-grabenstructuresalonghigh-

anglenormalfaultswhichjuxtaposeolder

andyoungerrocks(Fig.15A&B).

• Fracturesaremorelikelytobethrough-

goinginlayersofmorecompetentrock.

Conversely,fracturesweremorelikelyto

terminatewithinoratthecontactofabedin

thickerlesscompetentrock(Figure10A-D).

• Ingeneral,fractureswithineachoutcropcan

bedividedinto2sets:Set1averagestrike/

dipis223°/63°.Set2averagestrike/dipis

53°/55°(Figs.XA-D).Maximumpaleostress

directionscanbeinferredbasedonthis

conjugateset,roughlyNE/SWinthiscase

(Fig.16)

• RocksoftheBoquillasFormationtendtobe

morecalcareouswithcertainlayers

containinghigherclayandquartzcontent.

Overall,theBoquillasFormationatthis

locationismoreclay-poorthantheaverage

EagleFordShalecomposition(Figure13A&

B)

• Cross-plotsofXRFvs.UCSsuggestthat

strengthoftherockincreasesascalcite

contentincreaseandclaycontentdecreases.

Additionally,thedimplermethodshoweda

strongercorrelationwithelementaldata

thantheBambino.TheBambinorequiresa

relativelysmoothsurfacetotake

measurementsonwhilethedimplerdoes

not.Thiscouldbeonereasonforthe

differenceinUCSvalues(14A,B,&C).

B

A

Figure 15 A & B: Geologic map draped over a digital elevation model of Heath Canyon and the surrounding area. View looking south-southwest (A) and a view looking west-southwest (B).

ChihuahuaTrough

CoahuilaPlatform

Figure6:PaleogeographicreconstructionoftheNorthAmericancontinentduringthedepositionoftheBoquillasFormation(93.2Ma).Theblackovalsoutlinethe

approximatelocationoftheChihuahuaTrough(left)andthecarbonateplatformon

whichsedimentsweredepositedduringthistime(modiPiedfromBlakey,2017).

N

14miles(22km)

Figure4:LocationsoftheTransPecosregionofTexas(right,blackpolygon)andBlackGapWildlifeManagementArea(left,redpolygon).