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Compounds significant to the petroleum chemist concerned with petroleum exploration are those hydrocarbons possessing biological marker characteristics, that is, possessing intact steroid, terpenoid, and isoprenoid skeletons. These hydrocarbons are so closely related to the compounds occurring in the living organism from which petroleum was formed that they are capable of yielding very specific information regarding source, maturation, migration, and biodegradation of petroleum. Examples how source shales can be related to petroleum reservoirs using computerized gas chromatography/mass spectrometry, (GC/MS) are shown. The terpane GC/MS multiple array processor (MAP) approach can be used to differentiate source shales of different degrees of maturity and, thus, to determine source rock quality. Heavily biodegraded oils can be characterized and correlated by GC/MS fragmentograms of steranes and terpanes. Ratios of specific biomarkers obtained by quantitation from GC/MS data are used to differentiate oils of different degrees of migration. Examples from the exploration arena worldwide are given to illustrate these applications.

Paraho shale oil <260°C (500°F) was analyzed by gas chromatography/mass spectrometry (GC/MS) with the intent of establishing a preliminary set of guidelines and conditions under the auspices of ASTM for the GC/MS analysis of shale oil. A 60-m DURABOND-1, DB-1, fused silica capillary column coupled directly to our fast scanning 7070H double-focusing mass spectrometer was chosen. GC/MS operating parameters were selected so that the total ion monitor (TIM), GC trace would match that of a flame-ionization detector (FID) GC trace obtained previously under optimized conditions for a DB-1 column. Preliminary results show the presence of homologs of n-alkanes, isoalkanes, alkenes, or cyclic alkanes, alkylbenzenes, naphthalenes, indanes, tetralins, thiophenes, pyridines, indoles, phenols, and so forth. The data were reduced using an automatic quantitation INCOS computer procedure designed by J. Karnofsky specifically for this laboratory.

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Present concepts hold that the genesis of organic sulfur compounds is due mainly to secondary processes. The secondary process is a chemical reaction of oil with sulfur or sulfur species to give nonthiophenic sulfides and thiols first, then benzothiophenes, and ultimately stable dibenzothiophenes. This work describes the pyrolysis gas chromatography/mass spectrometry (GC/MS) identification of a homologous series of n-alkylbenzothiophenes extending from C10 to C30 in Arabian Heavy asphaltenes. Within each homolog there are at least 22 isomers. The mass spectra of these isomers typically show relatively intense molecular ions with base peaks at m/z 147, 161, or 175. The striking similarity of the fragmentation profiles of the homologous benzothiophenes and homologous n-alkylbenzenes also present in the sample strongly suggests that the benzothiophenes are generated directly from the reaction of the alkylbenzenes with sulfur species. Reflux experiments with known alkylbenzenes and elemental sulfur produced an abundance of thiophene derivatives including benzothiophenes.