Geochemical characteristics and significances of rearranged hopanes in hydrocarbon source rocks, Songliao Basin, NE China

Abstract

Abstract On the basis of GC/MS analysis, a suite of 56 core samples from the Songliao Basin in northeastern China was found to contain variable amounts of four series of rearranged hopanes: the 17α(H)-diahopane series (C29 diahopane and C30 diahopane), the 18α(H)-neohopane series (Ts and C29Ts), the early-eluting rearranged hopane series (C30 early-eluting rearranged hopane or 30E) and the 21-methyl-28-nor-hopane series (C29 28-nor-spergulane or 29Nsp). The results reveal that compounds in the same series of rearranged hopanes covary with each other closely, whereas linear correlations of four series of rearranged hopanes are diverse. On the whole, the 17α(H)-diahopane series shows an excellent correlation to the early-eluting rearranged hopane series. Both the early-eluting rearranged hopane series and the 17α(H)-diahopane series exhibit a general correlation with the 21-methyl-28-nor-hopane series. A general relationship between the 17α(H)-diahopane series and the 18α(H)-neohopane series is also noted. The 21-methyl-28-nor-hopane series and the early-eluting rearranged hopane series are not closely correlated with the 18α(H)-neohopane series. It seems that the rearranged hopanes show no covariance with some terpanes. Interestingly, rearranged hopanes display positive relations with C27–C29 αββ/ααα regular sterane or C27–C29 20S/20R regular sterane. Except for thermal maturity of hydrocarbon source rocks, this phenomenon is probably related to clay catalysis, mineral matrix or other factors.