Light hydrocarbon (gasoline range) parameter refinement of biomarker-basedoil-oil correlation studies: an example from Williston Basin

We evaluated geochemical compositions of 189 crude oils produced from Paleo zoic reservoirs across the Williston Basin. Emphasis is placed on compositi onal variations in the gasoline range (i-C5H12-n-C8H18) to verify the bioma rker-based classification of oil families. The oils belong to four distinct compositional oil families - A, B, C and D-broadly confined to specific st ratigraphic intervals. The unique character of each oil family, evident fro m their n-alkane and biomarker signatures, is supported by distinctive gaso line range characteristics in general, and C-7 ("Mango") parameters in part icular. An invariance in the K1 parameter among oils from a single composit ional group is observed for most of the oils. The K1 ratio, although relati vely constant within each suite of oils, is different for each oil family, clearly indicating their compositional distinction. Other Mango parameters (N2, P2, P3) show a similar reflection of the oil families. However, while C7 parameters provide excellent evidence for distinct familial association of oils from families A, B and D, family C often overlaps with the latter t wo families, perhaps indicating greater genetic and source heterogeneity in the family C oils. Nevertheless, differences in the gasoline range composi tion suggest that the existing biomarker-based classification of oil famili es can be more universally applied throughout the entire Williston Basin. M oreover, because the light hydrocarbon parameters prove very useful in refi ning oil-oil correlations, routine gasoline range analysis shows good poten tial as a supplementary component in geochemical correlation of crude oils, especially when high levels of thermal maturity decrease the usefulness of biomarker compounds. (C) 2000 Elsevier Science Ltd. All rights reserved.