Table Of ContentP
Petroleum: Chemistry and Occurrence components in solution which, in isolation, may occur in a
differentphaseatSTP.
JosephA.Curiale
GeochemicalAdvisoryServices,SugarLand,TX,USA (i) Gases – natural gas, including hydrocarbon gases and
higher-mass components dissolved therein, as well as
non-hydrocarbongases
Definition (ii) Liquids–condensatesandconventionalcrudeoilsdom-
inated by C to C components but also containing
6 60+
Petroleum is a naturally occurring mixture of hydrocarbon bothgasesandhigher-masshydrocarbonsinsolution
and non-hydrocarbon chemical compounds originating in (iii) Solids – solid bitumens generally resulting from early
sedimentaryrockspredominantlyfromthethermalalteration generation/expulsion from rich source rocks or from
ofonce-livingorganicmatterovertimeandatelevatedpres- degradationofaonce-liquidoil
sure.Thisarticleconcernstheoccurrenceandcompositionof
petroleumonandwithintheearth. Petroleumoriginatesfromtheactionoftemperaturesinthe
range of 50–250 (cid:1)C acting over geologic time periods
(105–109Ma)onorganicmatteraccumulatedinfine-grained
Introduction sedimentaryrocks (includingcoals).This descriptionof ori-
ginexcludestheconceptofabioticgeneration ofpetroleum,
This definition of petroleum is highly specific; it includes whichhasbeenstudiedbymanyoverthepasttwocenturies.
statements about both composition and origin. Other non- Abiotic petroleum is now considered to be an insignificant
specific terms, often used to indicate petroleum, are not cause of petroleum, is largely of academic interest, and will
appropriate. For example, “hydrocarbon” is a chemical notbediscussedinthisarticle.
definition – i.e., a molecule containing only carbon and The progressive thermal destruction of the insoluble
hydrogen–ofonetypeofchemicalcompoundinpetroleum, organicmatter(kerogen)andhigh-masssolubleandcolloidal
but this term is not synonymous with petroleum (because organic matter (bitumen) in sedimentary rocks commonly
petroleum also contains non-hydrocarbons). Likewise, oil, generates a supercritical fluid which resides in the pore
gas, asphaltenes, aromatics, etc., are phases of petroleum or space of sedimentary rocks in the deep subsurface. This
compound classes within petroleum, but again, these terms supercritical fluid often migrates to lower pressure-
arenotsynonymouswithpetroleum.Herewewilluse“petro- temperature regimes, and along the way it undergoes a
leum”asitisdefinedabove. phase change to gases and/or liquids. The compositional
Petroleum encompasses a compositional continuum characteristicsoftheresultingmixturedependuponthetype
extendingfrom methane and molecular hydrogen atthe low ofstartingorganicmatterinthesourcerockandthetemper-
molecular mass extreme to very high molecular mass ature and time experienced since its deposition. The infinite
asphalteneswhicharepresentasacolloidinliquidpetroleum. varietiesofstartingorganicmatterchemistriesandtime/tem-
Thus,atstandardtemperatureandpressure(STP)petroleum perature combinations lead to an extraordinarily large range
includesthreephasesasdescribedinFig.1andinmoredetail of petroleum compositions (Tissot and Welte 1984).
below. In the subsurface each of these phases contains
#SpringerInternationalPublishingAG2017
R.Sorkhabi(ed.),EncyclopediaofPetroleumGeoscience,
DOI10.1007/978-3-319-02330-4_1-1
2 Petroleum:ChemistryandOccurrence
exceed those recovered from conventional accumulations
(CurialeandCurtis2016).
Composition:Historical
Early compositional assessments of petroleum originated
fromrefiningeffortsandwerelimitedbytheanalyticalcapa-
bilitiesofthemid-twentiethcentury.Suchdescriptionsoften
characterized petroleum by the distribution of its distillation
fractions, yielding cuts described as “gas,” “light distillate,”
and“residual”or“bottoms.”Asliquidchromatographictech-
niqueswereintroducedandexpandedinthe1950sand1960s,
compoundclasseswere definedandnamed accordingtothe
dominant compound type, and compounds in specific series
wereoftendistinguishedbyaGreekprefix(Table1).Thisled
to compositional descriptions such as “paraffinic,”
“paraffinic-naphthenic,” “aromatic-intermediate,” etc., with
emphasis on the hydrocarbons and non-hydrocarbons sepa-
Petroleum: Chemistry andOccurrence, Fig. 1 Petroleums canbe
rated under the prevailing chromatographic conditions
describedbycomposition(totheright)andphase(totheleft). Three
fundamental types of chemical analysis are shown here – elemental, (Speers and Whitehead 1969). This compound class termi-
molecular, isotopic – and each analytical type applies to each of the nologyhasledtoseveralduplicativeandoverlappingterms;
threepetroleumphasesatSTP thisarticlewillemphasizethemostcommonlyusedterms.
Morerefinedliquidchromatographicandotherseparation
Migration of petroleum from its originating source rock, methodshaveledtothecompoundclassdesignationsinuse
along with subsequent changes induced by thermal, micro- today, including aliphatic (saturate) hydrocarbons, aromatic
bial, and evaporative effects, accompanied by variations in hydrocarbons, NSOs (nitrogen-, sulfur-, and oxygen-
pressureandtemperatureduringindustrialproductionofthe containing compounds; also called resins), and asphaltenes.
fluid,willfurthermodifyitscomposition. This latter fraction, though accessible via certain chromato-
graphic methods, is generally removed from the petroleum
initially, through excess addition of a low molecular mass
Occurrence solvent (e.g., n-pentane or n-heptane), and is considered to
existasacolloidinpetroleum(Yen1974).Withtheprogres-
The presence of sedimentary basins on all continents, the sively increasing influence of gas chromatography (GC),
exposureoftheirfine-grained sedimentstoelevated temper- mass spectrometry (MS), inductively coupled plasma (ICP)
atures over geologic time, and the occurrence of syn- methods,andvariousstableisotopemeasurementtechniques
depositional organic matter within these sediments have overthepastfivedecades,thesehistoricaldepictionsofcrude
made petroleum a ubiquitous constituent in earth’s crust. oil havegiven way todescriptionsbased onelementalcom-
Petroleumispresentinallphases–supercritical,gas,liquid, position,moleculardistribution,andstableisotopic ratiosas
and solid – on all continents, both on the surface and in the showninFig.1.
upper 10 kmof the crust. Surface and near-surface accumu- Numerous schemes have been proposed for naming the
lationsincludethevastasphaltandtarsanddepositsofwest- various compound classes and subclasses of petroleum, and
ern Canada, Madagascar, Venezuela, and elsewhere. Recent theseschemeshavespecificusesinupstreamanddownstream
economic extraction methods have made many of these segments of the petroleum industry. One example is the
deposits commercially viable. Subsurface petroleums subdivision of hydrocarbons that is abbreviated as PONA
reservoired in carbonates (limestones, dolomites) and and includes paraffins (also called saturate hydrocarbons),
course-grained clastics (sandstones, siltstones) account for olefins (compounds with double bonds between carbon
the majority of commercial accumulations. However, this is atoms), naphthenes, and aromatics (these last two are com-
changing as petroleum is increasingly extracted from fine- pounds with carbon rings in their structures). Most of these
grainedsource-rockreservoirunits.Currentestimatesinsome various schemes have been consolidated in upstream explo-
countriessuggestthatwithinthepresentcenturythevolumes rationeffortsinrecentdecadesintothatshowninTable1and
recovered from these unconventional accumulations will abbreviatedasSARA:saturatehydrocarbon,aromatichydro-
carbons,resins/NSOs,andasphaltenes.
Petroleum:ChemistryandOccurrence 3
Petroleum: Chemistry and Occurrence, Table 1 The compound is,althoughthesaturatefraction,forexample,isdominatedbyhydro-
typesinpetroleumareoftengroupedintocompoundclasses.Thischart carbons without multiple bonds, some separation procedures yield a
showsthemostcommonterminologyfortheseclasses,alongwithafew saturate fraction that contains some aromatic hydrocarbons. More
alternativenames.Theseclassfractionsaregenerallyobtainedvialiquid detailedclassificationschemesareprovidedinTissotandWelte(1984)
chromatographicanalysisandoftenarenotselectiveorexclusive.That andHunt(1996)
Commonclass Alternativeclass
terminology terminology Description Examples
Saturates Aliphatics; Dominantlyhydrocarbons,cyclicandacyclic,withoutmultiple n-paraffins;acyclicisoprenoids;
paraffins bonds aliphaticbiomarkers
Aromatics Dominantlyhydrocarbonswithatleastonearomaticring Naphthalenes,phenanthrenes;
aromaticbiomarkers
NSOs Resins;polars Dominantlycompoundscontainingheteroatoms,suchas Thiophenes;carbazoles;steroidal
nitrogen(N),sulfur(S),oroxygen(O) acids
Asphaltenes Tars Veryhighmolecularweightcompoundspresentinpetroleumas
acolloid
Petroleum:ChemistryandOccurrence,Table2 Thereareseveral chainhydrocarbonsandtheirderivativecompounds.Theitalicized“n”
terminological conventions for naming the chemical components of means“normal”andisintendedtoindicateastraightcarbonchain.The
petroleum.Thistableshowsthesimplestconventioninuse,forsimple originoftheprefixesforcarbonnumbersonethroughfourcomesfrom
hydrocarbonswithcarbonnumbersoftenandless.Thelistinggivesthe variousancientsources,e.g.,“propane”and“butane”arewidelythought
number of carbon atoms in the molecule and the names of the ten toderive,respectively,fromtheLatinwordforfatandtheGreekword
simplestn-alkanes.Allaremembersofthesaturatehydrocarboncom- forbutter.Prefixesforcarbonnumbersoffiveandgreatercomefromthe
poundclass.Alsoshownaretheprefixesusedtodesignatethesestraight Greeklanguage
Prefix Simplen-alkane
1 Meth- methane
2 Eth- ethane
3 Prop- propane
4 But- n-butane
5 Pent- n-pentane
6 Hex- n-hexane
7 Hept- n-heptane
8 Oct- n-octane
9 Non- n-nonane
10 Dec- n-decane
Because of the availability of precise methods of com-
pound separation, such as modern chromatographic tech-
niques, the use of compound class distributions is gradually
diminishing. In its place we have the capability of detailed
determinationsofthechemicalcompositionofpetroleumona Petroleum:ChemistryandOccurrence,Fig.2 Planardepictionsof
compound-by-compound basis. Conventions for individual structural configurations of methane (left) and n-heptane (right). The
compound names are much more specific than those for bonds shown for methane are intended to show its three dimensional
configuration,whereastheshorthanddepictionofn-heptanerequiresthe
compoundclassesandarelargelyspecifiedbynomenclatural
viewer to assume the presence of carbon and hydrogen atoms. More
rules of theInternational Unionof Pure andAppliedChem- detailsareprovidedinthetext
istry. IUPAC names as well as so-called “trivial” names are
currentlyinuseformanyofthecomponentsofpetroleum,the behind(dashedline)andoneinfrontofthepage.Incontrast,
simplestofwhicharelisted inTable2,for methane through theconfigurationshownforn-heptaneisfarsimplerandmost
n-decane. commonlyencountered:eachendpointandapexofthefigure
Each of the compounds shown in Table 2 – and indeed, are occupied by a carbon atom, and the bonded hydrogens
each chemical compound in petroleum – has a distinctive (not shown) necessary to account for each carbon’s valence
structural configuration, and multiple methods have been shellareassumedtobepresentbutnotshown.Forexample,
used to depict this configuration. Typical examples are three hydrogen atoms are present at each endpoint carbon,
shown in Fig. 2 for methane (left) and n-heptane (right). andtwoarepresentateachmid-chaincarbon.Inananalogous
Here,thethree-dimensionalexistenceofmethaneisdepicted manner it is possible to depict all of petroleum’s molecular
intwodimensionsbyshowingonehydrogenatomprojecting constituentsinarapidandconsistentmanner.
4 Petroleum:ChemistryandOccurrence
Petroleum:ChemistryandOccurrence,Table3 Examplesofter- The hydrocarbons of natural gases are commonly domi-
minologicalconventionsfornamingthecomplexhydrocarboncompo- nated by methane, although the total amount of ethane, pro-
nentsofpetroleumareshownhere.Thistableshowsabrieflistingof
pane, butanes, and pentanes often exceeds 5% by molar
howGreekprefixesareusedtonamevarioushydrocarbonsinpetroleum,
withexamplesgivenfromtheclassesofbiologicalmarkers volume. Olefinic hydrocarbons, such as ethene and propene,
alsooccur in a small numberofgases.Natural gases thatare
Number Greekprefix Example
dominantlyorexclusively methane,known asdry gases,can
1 mono- Monocyclicterpene
arise both from the action of microbial methanogenesis and
2 di-(variant:bi-) Bicyclicterpane
fromthehigh-temperaturethermaldegradationofsedimentary
3 tri- Tricyclicditerpane(e.g.,cheilanthane)
organicmatterorofotherpetroleums.Non-hydrocarboncom-
4 tetra- Tetracyclic(e.g.,sterane)
5 penta- Pentacyclic(e.g.,hopane) ponentssuchascarbondioxide,molecularhydrogenandnitro-
gen, helium, and hydrogen sulfide are also present in many
naturalgases.Withstandardizedanalyticalmethods,itispos-
In general, a Greek prefix along with accepted IUPAC sibletocharacterize,quicklyandaccurately,over99%ofthe
nomenclatureisalsousedforthemorecomplexhydrocarbons gaseouscomponentsinpetroleum.
inpetroleum,examplesofwhicharegiveninTable3.Using The liquid components of petroleum are assayed using
acceptednomenclaturessuchasthoseinTables2and3allows various chromatographic methods applied to whole oils and
petroleum geochemists to communicate effectively when theircompoundclassfractions(e.g.,aliphatichydrocarbons,
discussingthecompoundsofpetroleumandwhenassigning aromatichydrocarbons).Becauseoftheextraordinarydiver-
namestonewlydiscoveredcomponentsofpetroleum. sityinthesecompositions,thisarticlewillsummarizethemby
presentingmedianconcentrationrangesdefinedbychromato-
graphicclassand/orcompoundtype(Table1).Thebroadest
Composition:Elemental compositional distinction for liquids is that of hydrocarbons
versus non-hydrocarbons, with the former constituting
The elemental composition of petroleum, with few excep- 75–90%bymassofmostmid-range,non-biodegradedcrude
tions, is dominated by carbon and hydrogen (90%+). The oils (Tissot and Welte 1984). Among the hydrocarbons, the
so-calledheteroelementsofsulfur,nitrogen,andoxygencon- aliphatic fraction (i.e., those hydrocarbons without an aro-
stitute almost all of the remainder (Hunt 1996). In addition, maticring)accountsfor60–70%ofthetotalinmostunaltered
most of the remaining elements of the periodic table have petroleums (this excludes petroleums of extreme composi-
beenidentifiedinpetroleum.Thisincludes sub-percentcon- tion). Compound class categories are used to subdivide the
centrations of vanadium, nickel, cobalt, manganese, and aliphatic hydrocarbon fraction even further, into n-alkanes,
numerous other organically bound transition metals, which isoalkanes,acyclic,andcyclicisoprenoids.
arepresentmostlyintheasphaltenefraction.Tracelevelsof The remaining 30–40% of the hydrocarbon material in
other components, including (among others) mercury, arse- petroleum is commonly referred to as the aromatic fraction,
nic, and the noble gases, also occur as part of the inorganic which consists dominantly of aromatic hydrocarbons.
portion of petroleum, in both gases and liquids. Sensitive Because of the chromatographic processes commonly used,
high-precision analytical methods, including inductively however,thisfractionalsoincludesminoramountsofsulfur-
coupled plasma-mass spectrometry (ICP-MS), now make it and nitrogen-containing compounds. As with the aliphatic
possibletodeterminetheconcentrationsofmostelementsof hydrocarbons, the aromatic hydrocarbons can also be sub-
theperiodictableviaasinglechemicalanalysisofpetroleum. dividedintoadditionalclasses.Forexample,thisfractioncan
besegregatedaccordingtothenumberofaromaticringsper
molecule.
Composition:Molecular Althoughlessstudiedbypetroleumgeochemistsforboth
analytical and commercial reasons, non-hydrocarbons in
Earlyworkersquicklyrecognizedthatelementaldistributions crudeoilarefarmorecompositionallydiversethanthehydro-
within petroleum, while of interest from an economic and carbonsandincludenuclear,alkylated,andbenzylatedcarba-
refining perspective, were limited in assessing origin and zoles, thiophenes, pyridines, quinolines, and many other
history. In the mid-twentieth century, chromatographic and compound types. Organometallic constituents of crude oil
mass spectrometric methods were developed, largely within arerarelyspeciatedroutinely,althoughresearchhasindicated
the petroleum industry, as a way to identify the molecular thattheyaredominatedbyporphyrinicandothertetrapyrrolic
components of petroleum. This revolutionary development compounds,commonlymetallated(chelated)withnickelous
ledtoourhighlydetailedcurrentunderstandingofthemolec- andvanadylcations.
ulardistributionofbothhydrocarbonsandnon-hydrocarbons
inpetroleum.
Petroleum:ChemistryandOccurrence 5
Speciation and identification of hydrocarbons and the non- Composition:Isotopic
hydrocarbon constituents of liquid oils have benefited from
chromatographicmethodsaccompaniedbysophisticateddetec- Although elemental and molecular descriptions of a petro-
tionsystems,mostimportantlygaschromatography-massspec- leum provide an extensive assessment of its composition,
trometry/mass spectrometry, liquid chromatography-mass petroleums are also compositionally distinctive with respect
spectrometry,andmultidimensionalgaschromatographyusing tothedistributionoftheirstableisotopes.Thus,stableisotope
time-of-flight mass spectrometric detection (Eiserbeck et al. geochemistry is widely used to define the composition of
2012). Additionally, preparative chromatographic methods gases, condensates, oils, and solid bitumens and to assist in
followedbyinfrared,nuclearmagneticresonance,Raman,and understandingthematurationandmigrationhistoryoffluids.
otherformsofspectroscopyhavemadeabsolutestereochemical Indeed, petroleum compositional assessment in the absence
structuralidentificationpossibleinmanyinstances.Asaresult, ofisotopicdataisproperlyrecognizedasincomplete.Eachof
thousandsofspecificcomponentshavebeenidentifiedconclu- the five most common elements of petroleum – carbon,
sivelyasconstituentsofpetroleum.Amongthese,thehomolo- hydrogen, sulfur, oxygen, andnitrogen –possesses multiple
gous series in highest concentration in most unaltered stableisotopes,andstableisotoperatiosofallexceptoxygen
petroleums is the n-alkane series of hydrocarbons ranging arecommonlyusedbypetroleumgeochemists.Oftheratios
from C (methane) to greater than C (n-decacontane), inregularuse,averagecrustalvaluesforthesecondarystable
1 100
which can account for 10–30% by mass of the petroleum. In isotope range from less than 0.02% (2H, or deuterium, as a
unusuallywaxyliquidpetroleumsandinsomesolidbitumens, percentageoftotalhydrogen)to4.21%(34S,asapercentage
n-alkanescanaccountformorethan80%ofthemassoftheoil. oftotalsulfur)Thestableisotoperatiomostcommonlyused
Additionalhomologousseriespresentinpetroleumincludethe inpetroleumgeochemistryisthatof13Cto12C,whichhasa
acyclicisoprenoids(usuallydominatedbythewidelymeasured crustal abundance ratio of approximately 1:99. The propen-
and interpreted pristane and phytane components), the sityofstableisotopestofractionateduringprocessessuchas
alkylbenzenes, and the (loosely defined) cyclic isoprenoids. biotic growth, thermal cracking, and microbial utilization,
This latter group includes the bi-, tri-, tetra-, and pentacyclic causedbydiffusiveandkineticeffects,makesthemexcellent
aliphaticandaromaticcompounds(Table1)commonlyreferred toolsfordiscriminatingpetroleums.
toasbiomarkers. Isotopicdiscriminationofthecompoundsinpetroleumis
Molecular components inpetroleum whichshow a struc- greatestformethane,largelybecauseitistheonlycomponent
turally recognizable descendance from biochemical com- withadirectbiochemicalorigin.Thedualoriginsofmethane
pounds that are present in living (or once-living) organisms in petroleum – as a microbial product and as a thermal
arecalledbiomarkers.Thistermisacontractionof“biolog- product–arereflectedinthestableisotopicratiosofcarbon
ical marker” and refers to chemical compounds which are and hydrogen (Whiticar 1999). As an example, methane
molecular fossils. The separation and identification of bio- associated with petroleum in seeps and in the subsurface
markers in crude oils have yielded dozens of compound will exhibit carbon isotope ratios (d13C) ranging from less
classes whicharenowroutinelyusedtotracktheoriginand than (cid:3)100 o/oo to greater than (cid:3)20 o/oo depending on,
history of petroleums. A short list of these classes includes respectively, its microbial or thermal origin or mixtures
acyclic isoprenoids, cheilanthanes, phenanthrenes, steranes, thereof. Within this range, the d13C value of methane and
terpanes,andporphyrins(freebaseandchelated)(Petersetal. higher-massnaturalgascomponentswillvaryextensivelyas
2005).Althoughusuallypresentonlyatppmlevelsandless, a function of microbial consortia effective in the system,
the C26–30 steranes and C19–35 terpanes have received the original organic matter in the source rock, thermal maturity
most attention, largely because these components were level, extent of biodegradation, and possibly length and tor-
among the first identified and because they are remarkably tuosityofthemigrationpathway.Similarinterpretiveavenues
useful for interpreting the origin and history of liquid and existandareutilizedforotherisotopicratiosinnaturalgases,
solid petroleums. Modern gas chromatographic-mass spec- includingd2H,d15N,andd34S.
trometricanalysesthatareusedtoquantifythesecomponents Stableisotoperatiodistinctionsalsoexistinliquidpetro-
have evolved to the point where measurement is now rapid, leums and are caused by many of the same geological pro-
precise,andinexpensive.Thiscapabilityforrapidandaccu- cesses.Forexample,distinctionsarisefromthebroadsecular
ratedataacquisitionhasledtotheuseofpetroleummolecular variabilityofd13Cincrudeoils.Oilsoriginatingfromorganic
distributions, and particularly biomarker distributions, in a matterinsourcerocksolderthan0.5Gaareoftenisotopically
wide variety of applications. These include assessment of lighterthan(cid:3)33o/oo,whereasthoseoriginatingfromorganic
source-rockoriginandcharacter,thermalmaturityattimeof matterinsourcerocksyoungerthan20Macanbeisotopically
generation, relative subsurface migration extent, and degree heavierthan(cid:3)20o/oo.Inaddition,(i)thermalmaturityextent
ofthermal,microbial,andevaporativealterationafterexpul- is often deducible from carbon and hydrogen isotope ratio
sionfromthesourcerock. data, (ii) depositional setting of the source unit (e.g., open
6 Petroleum:ChemistryandOccurrence
marinevs.freshwaterlacustrine)canbeapparentfromhydro- Cross-References
gen isotope trends, and (iii) origin of sulfur-rich gas can be
deduced from the sulfur isotope ratio of hydrogen sulfide. ▶BasinandPetroleumSystemModeling
These are but a few of the uses for stable isotope measure- ▶Hydrocarbons:Origin
ments as tools for assessing petroleum origin. The broad ▶PetroleumGeochemistry
applicationofstableisotoperatiosinpetroleumgeochemistry ▶Petroleum:PhysicalProperties
hasmadetheseparametersanecessaryadjuncttoanyrobust
compositionalanalysisofpetroleum.
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P
Petroleum Geochemistry HistoricalDevelopment
JosephA.Curiale The historical development of petroleum geochemistry as a
GeochemicalAdvisoryServices,SugarLand,TX,USA distinct discipline evolved from the convergence of several
priorsciences,includingchemistry,geology,andbiology,and
their sub-disciplines as depicted in Fig. 1. Following the
Definition Industrial Revolution, extensive observations of bedded
coals led to early theories which proposed that liquid and
Petroleum geochemistry is the science and application of solid crude oils originated from coal and its precursor peat
chemical concepts to understand the origin of deposits,andmosttreatisesontheoriginofoildatingfromthe
petroleum – natural gas, condensate, and crude oil – and its eighteenthandnineteenth centuries reflecttheseideas (Hunt
occurrenceandfateontheearth’ssurfaceandwithinitscrust 1996;Dott1969).Moredetailedchemicalstudiesduringthat
(adaptedfromHunt1996). period addressed compositional similarities between liquid
oiland animal orplantcomponents,leadingtotheoriespro-
posingthatfishoilandplantpigmentswerestartingmaterials
Introduction foroil.Althoughmanyoftheseearlytheoriesmaybethought
fanciful today, they eventually led to the seminal work of
Themostextensivedevelopmentofpetroleumgeochemistry AlfredTreibs(Treibs1934).Compositionalanalysisofplant
hasbeeninanindustrialsense,becausepetroleumgeochem- pigments,includingchlorophyll,ledTreibstopositagenetic
ical principles are applied widely in exploring for, develop- relationship between once-living organic matter and petro-
ing, and producing petroleum. Petroleum geochemical leum.Similaritiesevidentintetrapyrrolicchemicalstructures
concepts are also applied in such diverse areas as environ- identified in both substances ultimately led to a working
mental studies, forensic applications, archeological and hypothesis in which living organic matter is the starting
anthropological studies, and the search for present and past point inachain ofevents that eventuallyleads totheoccur-
evidenceofextraterrestriallife. renceofnaturalgas,condensate,andcrudeoil.
Thisarticlefocusesontheuseofpetroleumgeochemistry FollowingtheinsightsestablishedbyTreibsandthesub-
inunderstandingthesource,maturation,migration,andalter- sequent widespread commercial exploitation of petroleum,
ationofpetroleumintheearth’suppercrust,wherepetroleum progress in petroleum geochemistry was intermittent over
is considered to encompass a molecular continuum from the next few decades. Early understanding of the chemistry
naturalgastoliquidandsolidoil.Moreextensivediscussions of petroleum came predominantly from refinery science and
are provided in several textbooks and technical reviews, inparticulartheneedtounderstandinputchemistryinorderto
includingTissotandWelte(1984),Hunt(1996),Killopsand “tailor”specificoutputproducts.Theseadvancesbeganwith
Killops(2005),andPetersetal.(2005). methodical and painstaking compositional studies in indus-
trial or industry-supported organizations, most notably the
American Petroleum Institute, as outlined in chronological
detail in Hunt et al. (2002). Most importantly, however,
research efforts at this time were initiated following the
development of integrated laboratories within the petroleum
#SpringerInternationalPublishingAG2017
R.Sorkhabi(ed.),EncyclopediaofPetroleumGeoscience,
DOI10.1007/978-3-319-02330-4_2-1
2 PetroleumGeochemistry
PetroleumGeochemistry,
Fig.1 Petroleumgeochemistryis
aninterdisciplinarysciencewhich
drawsuponconceptsanddata
fromnumerousotherdisciplines
industry and governmental organizations worldwide, and it organic matter to petroleum (correlation science). By the
waswithintheselaboratoriesthatmostadvancesweremade mid-1990s, these concepts were firmly established (e.g.,
during the last half of the twentieth century and, in some Peters and Moldowan 1991; Curiale 1993; Whiticar 1996),
cases,continuetothepresent(Table1). anddevelopmentssincethenhavefocusedonenhancedana-
Inalmostallinstances,conceptualdevelopmentsinpetro- lytical capabilities accompanied by the incorporation of
leumgeochemistrywereprecededby,orcoincidentwith,the petroleumgeochemistryasasignificantandinvaluablecom-
advent of instrumental techniques specifically suited to ponentofourunderstandingofpetroleumsystems.
unraveling the complex chemistry of petroleum. The most The key ongoing development in the field, from both a
criticaltechniquesfromthisperspectiveweregaschromatog- conceptual and applied perspective, is the increasingly tight
raphy and coupled gas chromatography-mass spectrometry, interrelationship between petroleum geochemistry as a tool
isotopemassspectrometry,andsimultaneousmulti-elemental forunderstandinghydrocarbonchargeinsedimentarybasins
analysisofcomplexorganicmixtures.Upondevelopmentof and the additional risk elements used to assess petroleum
theseanalyticalmethods,manyorganicchemistsshiftedtheir systemsinthesebasins.Theseincludereservoirquality,seal
research focus to the rapidly expanding field of petroleum quality, and structural configuration. Modern integration of
chemistry.TypicalexamplesincludeearlyworkbySilverman petroleum geochemistry with petroleum system science has
andEpstein(1958)oncarbonisotoperatiosoforganicmatter provided academic scientists as well as petroleum
andstudiesonearlygeochemicalapplicationsofgaschroma- explorationists with a powerful approach for understanding
tography (Cooper and Bray 1963). These early studies, the generation, migration, and entrapment of oils, conden-
including the strong emphasis on analytical chemistry, were sates,andgases.Continuingdevelopmentsarechronicledin
summarizedinthe1960sinvolumeseditedbyBreger(1963) numeroustechnicaljournalsandseveralinternationalconfer-
andEglintonandMurphy(1969).Thecontentofthesecom- ences. Among these, the most prominent are, respectively,
pilations is still relevant today. Detailed timelines and key Elsevier’s Organic Geochemistry journal and the European
contributors throughout the twentieth century are listed in AssociationofOrganicGeochemistry’sInternationalMeeting
Huntetal.(2002)andKvenvolden(2006). onOrganicGeochemistry.Table1presentsacondensedver-
Theinstrumentaldevelopmentsthatdrovepetroleumgeo- sion of seminal contributions to the development of petro-
chemicalresearchinitsearlydays(Table1)ultimatelyledto leumgeochemistryinthetwentiethandtwenty-firstcenturies.
theconceptswhichnowformthebackboneofthediscipline. Anexcellenttimeline,arecordofcontributorstojournalsand
Theseincludethenaturalgeneration ofpetroleumhydrocar- conferences, and related photographs are provided by
bons from source rock organic matter derived from plants Kvenvolden(2006).
containingstructurallyanalogousnon-hydrocarbonbiochem-
ical components (now commonly referred to as biomarker
geoscience),thenaturalfractionationofcarbonandhydrogen MajorSub-disciplines
isotopes from precursor organic matter during the origin of
petroleum (isotope geoscience), and the use of molecular The three major sub-disciplines of petroleum geochemistry
markers, isotopic ratios, and elemental distributions to link (Fig. 2) – elemental, molecular, and isotopic
components along the transformation route from living geochemistry – collectively identify and quantify the 104 to
PetroleumGeochemistry 3
PetroleumGeochemistry,Table1 Keydevelopmentsinpetroleumgeochemistry.ForgreaterdetailseeTissotandWelte(1984),Hunt(1996),
Huntetal.(2002),andKvenvolden(2006)
Year Historicaldevelopment
1927 AmericanPetroleumInstituteProject6isinitiated,methodicallyidentifyingthehydrocarbonsinasinglecrudeoilforthe
firsttimeandleadingtonewdevelopmentinseparationscience
Early1920stoearly PetroleumgeochemicalanalysisofsoilgasesinEurope,Asia,andNorthAmerica,openingtheeraofpetroleum
1930s explorationviaanalysisofnear-surfacehydrocarbons
Early1930s AlfredTreibsandcolleaguesestablisharelationshipbetweenmetalloporphyrinsinoilsandchlorophyllinlivingorganic
matter,anticipatingthebiologicalmarketconcept
Early1950s Thefirstindustry-basedandcausallydefinedoil-oilandoil-sourcerockcorrelationsareconductedasearlyindustry
geochemicallaboratoriesbeginpetroleumgeochemistryresearchprograms
Late1950s Earlystablecarbonisotopeanalysesareadaptedforuseingeochemicalorganicmatter,includingcrudeoilsandorganic-
richrocks.Immediateusesarefoundincorrelationstudies
Early1960s Gaschromatographic(GC)analysesareappliedtoanalyzehydrocarbonsingeochemicalorganicmatter.Mass
spectrometryisutilizedinthedecadeasaGCdetector,resultinginanexplosionofcompoundidentificationsinoilsand
rockextracts,andtheeraofmodernbiologicalmarkeranalysisinpetroleumgeochemistrybegins
Late1960s Organicpetrographystudiesareconductedonorganicmatterinpetroleumsourcerocks,andthefirstvitrinitereflectance
laboratoryisestablishedinthepetroleumindustry
1970s Mostlargeenergycompaniesestablishin-housechemistrylaboratoriesdevotedtoresearchontheoriginofoilandgas.
Forthefirsttime,petroleumgeochemicalanalysesandinterpretationsarewidelyappliedtoexploration,development,
andproductionproblems
Late1970s Automatedpyrolysismethodsaredevelopedandbecomecommerciallyavailable,providingrapidandreproducible
assessmentofpetroleumsourcerockpotential
1980stopresent Newmethodsofchemicalanalysisareadoptedbyexplorationists;numericalmodelingisusedtoestimatepetroleum
generationtimingandproductsatthebasinscale;petroleumgeochemistrybecomesanecessarydisciplineinallpartsof
theindustryvaluechain
105 hydrocarbon and non-hydrocarbon components present whichfocusedoncarbonisotoperatiosofspecifichydrocar-
inpetroleum. bonclassesinpetroleum,evolvedinthetwenty-firstcentury
Elemental compositional studies focus on the non- intotheroutinelyappliedpresent-daymethodofcompound-
hydrocarbons present in petroleum fluids, including compo- specificisotopicanalyses(CSIA)wherebycarbonandhydro-
nentssuchasHeandHginnaturalgases,andsulfur,nitrogen, gen stable isotope ratios of individual components are mea-
oxygen,andtransitionmetals(e.g.,vanadium,nickel,cobalt, sured. CSIA instrumentation, initially commercialized for
manganese) in liquid oil and solid bitumen. Raw elemental carbon and then for hydrogen and other elements
concentrations and specific elemental ratios are used as cor- (Schimmelmann etal. 2006),provides a highly specific tool
relativetoolsandasameanstoevaluatetheoriginandhistory fordistinguishingonepetroleumfromanother.
ofaspecificpetroleum. Taken together and used holistically, the petroleum geo-
Moleculargeochemistryfocusesonthespeciationofthese chemistrysub-disciplinesofelemental,molecular,andisoto-
elements in petroleum. In a full-spectrum petroleum pic geochemistry are required tools for understanding the
consisting, at standard temperature and pressure, of natural originandsubsequentchemicalalterationofpetroleum.
gas,condensate,andcrudeoil,themolecularsuitespresentin
the petroleum are wide-ranging. They extend from low
molecular-mass components such as molecular hydrogen Applications
and methane to acyclic and cyclic higher molecular-mass
hydrocarbons and non-hydrocarbons and ultimately to Because the discipline of petroleum geochemistry evolved
extremely high molecular-mass asphaltenes that are present over the last several decades largely as a tool used by the
inliquid oilsasacolloid. Overthepasttwodecades,devel- energyindustryinpetroleumexploration,theapplicationsof
opmentofeverhigher-resolutionseparationmethodsaccom- petroleum geochemistry focus on the relationship between
panied by highly specific detection techniques has made petroleumanditssourcerockandonchemicalmodifications
molecular analysis and interpretation the most commonly that occur to the petroleum after it migrates away from its
used sub-discipline of petroleum geochemistry (Peters source location. These applications can be classified as
etal.2005). (i)genetic–i.e.,compositionalaspectsimpartedtothepetro-
The third sub-discipline, isotopic geochemistry, presents leum by the organic matter in its source rock – and
theidealcomplementtoelementalandmolecularevaluations. (ii)nongenetic.Thelatterincludesapplicationsofpetroleum
Compound class isotopic analyses of the twentieth century, geochemistrytounderstandand,insomecases,quantifythe
4 PetroleumGeochemistry
PetroleumGeochemistry,Fig.2 Elemental,molecularandisotopicgeochemistrycomprisethethreesub-disciplinesofpetroleumgeochemistry.
Shownherearejustafewofthemanyanalyticalapproacheswhichcontributetothediscipline
extentofin-sourceandpost-sourcethermalmaturation,fluid absolute temperature – at the time of generation and expul-
migration, and post-entrapment/in-reservoir compositional sion,(c)determinationofalacustrineversusamarinedepo-
alteration.Theconceptualunderpinningoftheseapplications sitional setting, and (d) if lacustrine, an inference of saline
arises from the understanding that a petroleum’s chemical versus freshwater conditions in the depositional water col-
composition contains a full complement of information umn.Evaluationofsourcerockcharacterthroughpetroleum
about its origin and its post-sourcing history. Based upon compositionalanalysiscontinuestobeoneofthemostactive
thisfundamentalprecept,thepetroleumgeochemistattempts areasofpetroleumgeochemicalappliedresearch.
to interpret the compositional data of a petroleum in such a The compositional modifications that occur in petroleum
way that all genetic and nongenetic compositional changes after it is expelled from the source rock(s) can be assessed
are deciphered and the full history of the petroleum is through a combination of the elemental, molecular, and iso-
understood. topic sub-disciplines of petroleum geochemistry. Both the
Historically, the application of petroleum compositional specific pathway and the relative extent of the migration
analysistoourunderstandingofapetroleum’sorigin,includ- journey from source rock to the entrapment volume may be
ing the identity and depositional conditions of its source estimatedusingmoleculartechniques.Thisoccursbecauseof
unit(s) and the conditions of its generation (temperature, the progressive depletion of high molecular-mass compo-
pressure,compositionofassociatedwaters,etc.),isthemost nents and the post-sourcing uptake of exogenous molecular
commonuseofpetroleumgeochemicaltechniques.Through species caused by, respectively, progressive migration dis-
combining elemental, molecular, and isotopic analyses of a tance and contact with specific and distinct organofacies
petroleum, it is now possible to retrodict the character of its during migration. Compositional changes in petroleum fol-
sourcerockwithvaryinglevelsofsuccess.Forexample,age lowing entrapment can be evaluated in order to determine
andlithologyofthesourceunitcanoftenbeestimated,ascan numerousfeatures ofpetroleum history, including (a) extent
its depositional environment, organofacies, and thermal his- of light-end loss due to evaporation; (b) loss of specific
tory,fromthecompositionofitsexpelledpetroleum.Molec- (usuallyaromatic)componentsduetopreferentialdissolution
ularandisotopicanalysesalsoprovidetoolsfordetermining into the accompanying water phase; (c) decrease in overall
if multiple source units, or multiple organofacies within a molecular mass of the fluid, caused by thermal effects; and
single source unit, are responsible for a specific petroleum. (d) compositional modifications caused by microbial con-
Focusedapproacheshaveachievedimpressivelevelsofsuc- sumption(biodegradation)ofselectedmolecularseries.
cess.Forexample,crudeoilcompositionalanalysisandinter- Althoughpetroleumgeochemicalapplicationshavetradi-
pretation often allow (a) assignment of source age, in some tionallyfocusedon theexplorationfor petroleum, both field
cases to within 20–30My (e.g., Holba et al. 1998), development and production efforts also benefit from the
(b) estimation of source rockmaturity –and, insome cases, application of petroleum geochemical techniques. Indeed,
