1. Experimental Study of the Pyrolysis of Eagle Ford Oil Shale
Abstract
Witha greatdeal of researchandinvestmentbeingfocusedonthe developmentof
unconventional fuels,the UnitedStates’domesticoil shale resourceshave beengivensignificant
considerationasaviable source fordomesticfuel.Geochemical andgeophysical assessmentsof oil and
gas potential providecritical informationrelevanttothe extractionandproductionstrategies.
Sequentiallaboratorypyrolysisexperimentswillbe conductedunderdifferentconditionsincluding
hydrous,anhydrousandpyrolysisinthe presence of hydrogengasonbothwhole rockand kerogen
extractedsamplesfromEagle Fordshale deposits. Thisstudywill:(1) analyze immaturesamplesof
these source rocks,(2) characterize theirgeneratedoil andgasproductsduringpyrolysisexperimentsto
evaluate theirpotential assource rocksand(3) improve retortingmethodsof oil shaleforpetroleum
production.The use of gas chromatographyandmass spectrometrywill be usedtoanalyze the
recoveredgaseousandliquidcompositions.A seriesof compoundsingeneratedoils,the bulk
compositionof generatednatural gas,andthe carbon isotopiccompositionof methane innatural gas
provide informationoncompositions astheyevolve withincreasingthermal stresswill provide useful
insightintofuture unconventional resource assessment.
1. Introduction
Mudrocks withlarge amountsof organicmatter are some of the mostcommon source rocks for
hydrocarbons. Oil shale referstothermallyimmature shalerockcontainingkerogen,whichistypically
foundat depthsof <3000 feetwithinsedimentarybasins. Asthese oil shalesare thermallyimmature,
mostof the kerogenwithinthemremainsintactandcapable of producingoil andgas. The UnitedStates

2. Eq. 1 The added heat and pressure to organic compounds, lipids, fats and carbohydrates
form long chain hydrocarbons (geopolymers)
possessesapproximately1.5trillionbarrelsof “recoverable”oil reservesinnear-surfaceshale deposits,
whichaugmentsthe significantresource potentialindeepershale depositsthatare the currentfocusof
oil and gas exploitation(Mao2010).
The Chemistry of Petroleum Formation
At itsbase,petroleumisafossil fuel,whichmeansitis derivedfromthe remainsof organic
material.Inotherwords,petroleumresultsfromanumberof chemical reactions thatoccur to material
that wasonce alive.Inmostcases,liquidpetroleumwasonce zooplanktonoralgae thatsettledtothe
bottomof a seaor lake and was thenburiedundersediment.The sedimentensuredthatnooxygenwas
able to reachthe decayingorganicmatterandthisset the stage for the formationof oil. Overgeologic
time,thisorganicmatterissubjectedtoincreasedpressure from overlyingsediment andheatasthese
rocks are buriedmore deeply (Fig.3).The solidificationandconversionof thisorganicmatter,itisfirst
changedintoa waxysolidcalledkerogen foundinsedimentaryrocksincludingshaleandcoal.This
processwhere kerogenisformedis calleddiagenesis,whichcanbe seenin (Eq1).
Catagenesis
As temperature andpressure continuestoincrease fromsedimentaccumulation, the
processof catagenesisbegins.Catagenesisisthe thermal degradation (or“cracking”of heaviercarbon
bonds) of kerogentoshortermore straight/branchedhydrocarbonchains (Figure 1a).Since the
behaviorof petroleum formationisdependentonheat, pressure andmolecularstructure,averyspecific
range of temperaturesandheatingratesare requiredtoproduce aqualityproduct.If conditionsare too

3. hot,the hydrocarbonsformedfromcatagenesiswillfavoran aromaticring chemical structure (Figure
1b), beingcharacteristicof natural gas.If temperaturesdonotexceedthe energythresholdtobreakthe
kerogen(itvariesfromdifferentkerogentypes) the biological precursors will remaintrappedas
kerogen.
Petroleum production by artificial maturation of oil shale
Simulatingcatagenesisthroughlaboratorypyrolysisexperimentsisfrequently usedtoattempt
to replicate the compositionof the yieldsseeninnature,inaslittle as12 hours. “The differencesin
time-scale betweenthe laboratoryexperimentsandnatural geological processesare sogreatthat claims
of irrelevance andmechanismsare difficulttorefute. (SaxbyandRiley,1984). Lewanand others(1979)
reportedthatheatingorganic-richrockssubmergedinliquidwater resultedinthe generationand
expulsionof free flowingoil thataccumulatedonthe watersurface above the submergedrock.
Knowledgegainedthroughthe manipulationof experimental conditionstoproduce useful fuelswas
appliedtothe problemof producingalaboratory-scale analogforpetroleum-formingprocesses.Evans
and Felbeck(1983a, b,c) performedaseriesof experimentsdesignedtoexamine the hypothesisthat
hightemperature reactionscouldbe usedtosimulatepetroleumformation.Theyfoundthatthe closed-
systempyrolysisof anoil shale couldbe usedtoduplicate the observationsof manyinsitustudiesof
petroleummaturation.Throughthe pyrolysisof oil shale,theywereable todefinefivedifferent
temperature zonesthatsimulatedpetroleummaturationreactions(EvansandFelbeck, 1983a).
Figure2. Left:Aromatic,three double
bonded carbonsin a ring structure.Good
indicatorof high thermalmaturityRight:
Common aliphatic carbons indicative of low
thermal maturity.
Fig. 1 Summary of the oil formation process, modified from Tissot and
Welte, 1984

4. 2. ResearchObjectives
The objective of this research is to investigate the composition and quality of generated
petroleum and gas of the Eagle Ford Formation from laboratory simulated hydrous pyrolysis
experiments.The goal will be to apply various time-temperature conditions (12hr-24hr and 280-
330°C ) of thermally immature organic-rich samples containing type-IIkerogen. This will aid in
assessing reaction pathways and controlling factors to determine the generation of petroleum (gas
and oil) as well as the effects of maturation of marine shales.
Eagle FordFormation
The Eagle FordFormation waschosenfor thisstudy.It outcropsalonga northeast-southwest
trend,spanningfromOklahomadowntosouthwesternTexas(Figure1). The unitdipsat aboutone
degree tothe southeast. The thicknessof the Eagle Fordvariesregionallyanditisabout 200ft thickin
the Waco areabut thinsto the southwesttowardAustin(Jiang,1989).
Study area
Outcrop trend

5. Fig 3 Outcrop trendof the Eagle Fordthroughoutcentral Texas.Modifiedfrom (Dawson,
2000)
The depositionof the Eagle FordFormationoccurredduringthe Late Cenomanianand
Turonianstagesof the Late Cretaceous.Duringthistime,agenerallywarmclimate withrelativelyhigh
atmosphericpCO2 levelsdominated(Veizeretal.,2000; Bice et al.,2006). Global eustaticsealevel
reachedthe Cretaceousmaximumfollowingaprolongedrise insealevel(Haqetal.,1987) and the poles
were ice free.
3. Methodology
SamplePreparationand CharacterizationofWholeRock and Kerogen
Shale samplesfromthe Eagle Fordformationwill be manuallycrushedwitharockhammer,
thenmilled intoafine powderusingashatterbox. The shale sampleswillbe characterizedbyoptical
microscopyof thin-sections,X-raydiffraction,andscanningelectronmicroscopybefore andafterthe
proposedpyrolysisexperiments. The large variationinbiological precursorsandthe modifications
broughtabout viadiagenesisandcatagenesiscreatesacomplex heterogeneousstructure affecting
chemical bondstrength.If the molecularstructure of kerogendeterminesitspetroleumgeneration
products by alteringchemical bonds,itwill require adifferentthermal energytobreakthe gaseous
molecularprecursorsfromthe kerogen. Althoughitisnotpart of the natural petroleumformation
process,solidkerogenextractionbydemineralizationpreventscatalyticreactionsordecompositionof
mineralswithinthe system(Saxby1982).
Approximately 8gof whole-rockpowderwillbe weighedintoa50mL polyethylenecentrifuge
tube.Carbonates will be removedbytreatmentof sedimentwith 1N hydrochloricaciduntil

6. effervescenceceased.The resultantsupernatantliquid will be decanted.Subsequently,the rocks will be
furtherdemineralizedusingthree successivetreatmentswith25mLdosesof mixedhydrofluoricacid(10
wt.%) andhydrochloricacid(10 wt.%).Each treatment will occurfora minimumof 12 hourswhile
shakingonan orbital shaker. Aftercentrifugationat5,000 rpm, the pelletwill be rinsedwithdeionized
water3 times.The samples willthenbe driedovernightinaheatedsandbathat 50°C.
Organicmatter inthe original shale samplesandextractedkerogensampleswillbe
characterizedfortotal organiccarbon (TOC) and itsδ13
C valuesbyelemental analyzer–isotope ratio
mass spectrometer,differenttypesandfractionsof organicmatterbyRock-Eval (GEOMARKRESEARCH,
LTD) and nuclearmagneticresonance spectrometry(BaylorUniversity).
The Rock Eval methodentailsa programmedheatingof asedimentsample(100mg) inan inert
(heliumgas) atmosphere. Volatile productsfromthe pyrolysisare measuredbyaflame ionization
detector.Briefly,the temperature programisasfollows.The oventemperature isheldat300°C and the
free hydrocarbonsare volatilizedandmeasuredasthe S1 peak(detectedbyFID).The temperature is
thenincreasedfrom300° to 550°C (at 25°C/min).Thisisthe phase of volatilizationof the heavy
hydrocarbons(>C40) andthe crackingof nonvolatile organicmatter(kerogen).The hydrocarbons
releasedfromthisthermal crackingare measuredasthe S2 peak.The temperature atwhichS2 reaches
itsmaximumdependsonthe nature andmaturityof the kerogenandiscalledTmax.The CO2 from
kerogencrackingistrappedinthe 300°-390°C range.The trap is heated,andCO2 isreleasedand
detectedona thermal conductivitydetectorduringthe coolingof the pyrolysisoven(S3peak). Usingthe
isotopiccompositionvaluesvsthe standardRock Eval valueswill give usanideaof how successful the
independentexperimentsworkedaswell asaidingincharacterizationof the oil shale samplescollected.
Isotopiccompositionof methanewill alsogive astrongindicationof thermal maturity,acomponentof
source rock evaluationthatisalwaysa necessity.

7. PyrolysisExperiments
The experimentswillconsistof iso-thermallyheatingtensof gramsof gravel-sizedimmature
source rock and extractedkerogen inthe presenceof liquid waterinabomb reactorat temperatures
reaching330°C for 12-36hrs. The pressure will be controlledtothe saturationpressure inthe presence
of water(130 bars).Afterthe experimentiscompleted,gaseousandliquidcompositionswill be
recoveredanddeterminedbymassspectrometryandgaschromatography.The remaininggaswill be
ventedandthe reactor will be openedtoquantitativelycollectthe expelledoil.These laboratory
pyrolysisexperimentswill simulate natural occurrencesof catagenesisbyexponentiallyaccelerating
geologicprocessesthroughincreasedtemperatures. Kerogenwill be extractedfromeachsample using
a sequestrationtechniquetoenhance qualitative understandingof the controlsongasgenerationfrom
source rocks and expelledoil containingtype-IIkerogen
AnalysisofPyrolysisproducts
Usinggas chromatographyand massspectrometryitishopeful we willbe able toboth
quantitativelyandqualitativelyhave adeeperunderstandingof the maturationprocessonthe
molecularlevel andtobe able to predictthe quantityandtype of expelledhydrocarbonsbeforethe
artificial maturationexperimentbegins.If successful,thiswill be amajorbenefitinfuture source rock
evaluationsbeingable tosave bothtime andmoney.
Upon analysisof the pyrolysisproductsIexpect thatδ13
Cvaluesof C1 and C2 alkanesincrease
withtime,butwill notbe the case for C3 and C4 after72 hrs. Overall,δ13
Cof C1 – C4 alkaneswill follow
the “thermogenic”trendatthese specificexperimental conditions,basedonpreviousstudiesformthe
Universityof Houston.

8. The resultsof the laboratorypyrolysisexperimentswillbe correlatedusingthe industry
standardof Rock Eval pyrolysis,whichwill be facilitatedatGeoMark Labs,locatedinHumble,Tx.Rock-
Eval PyrolysisProcedure.
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