Hydrocarbon Accumulations in Paleozoic Strata in Anadarko Basin in Kansas

John G. Schumacher, S. Chaudhuri

Crude oil samples from several different Paleozoic strata within a 5,000-mi² area in the Anadarko basin in western Kansas were analyzed for their organic compositions, trace element contents, and carbon isotopic compositions to determine genetic relationships among the hydrocarbons. The oils had moderately high API gravities (29°-47°) and low sulfur contents (less than 0.5% by weight). The pristane/phytane ratios ranged from 1.2 to 1.7. Based on the trend of normalized concentrations of the isoprenoids between iP-13 and iP-20, the oils may be broadly divided into two types, one enriched in iP-13 and iP-16 and the other enriched in iP-19. The latter type may be further differentiated into three subtypes based on relative depletions of other isoprenoids. The oils with iP-13 and iP-16 enrichment are restricted to the southern part, whereas the oils with iP-19 enrichment are located in the northern part of the area. Both vanadium and nickel contents, ranging between less than 0.4 and 57 ppm and between less than 0.2 and 11 ppm, respectively, increase northward (r = 0.52 for V and 0.42 for Ni). Following Lewan's interpretation of the V/(V + Ni) values, all the oils derived from a marine-dominated source in a moderately oxidizing environment. The ^dgr¹³C values of the oils, ranging between -28.8 and -30.4, correlat negatively with increased distance northward (r = -0.87). The geographic trends seen in the geochemical parameters of the oils are most easily explained by a mechanism of differential entrapment of multiple oil types.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.