biomarker application in the recognition of the geochemical characteristics of crude oils from the five depobelts of the niger delta basin, nigeria

Biomarker fingerprints of crude oils are useful indicators of origin of organic matter input in source rocks and depositionalconditions which are useful indices for petroleum systems development within a hydrocarbon producing horizon. twenty five (25)crude oil samples from the five depobelts of the niger delta basin, nigeria were studied to describe their biomarker fingerprints,provide information on the origin of organic matter input in the source rock(s), determine depositional environmental conditions andthermal maturity of the crude oils. the study was based on biomarkers (steranes and hopanes), normal alkanes and acyclic isoprenoids(pristine and phytane) obtained from the gas chromatography–mass spectrometry (gc-ms) analyses performed on the saturatedfractions of the crude oils. the results of pristine/phytane (pr/ph) ratios, pr/n-c17 ratios, ph/n-c18 ratios, c29/c27 sterane ratios,sterane/hopane ratios, %c27, %c28 and %c29 regular steranes, oleanane index, waxiness index, ts/tm ratios and carbon preferenceindex (cpi) values, indicated that the analyzed crude oils belong to the same family of oil and originated from terrigenous clasticsource rock (s) containing land plant organic matter with minor marine organic matter input, deposited under oxic to sub-oxicpaleoenvironmental conditions. the pr/n-c17 versus ph/n-c18 cross plot indicated marine algal type ii and a mixed type ii/iii kerogen.the c32h:22s/(22s+22r) values together with ts/(ts + tm), c29:20s/20s + 20r, oleanane index and cpi values indicated that mostof the crude oils have reached thermal equilibrium with high thermal maturity levels.