Geochemical characteristics and applications of 18 alpha(H)-neohopanes and17 alpha(H)-diahopanes

Distributions and geochemical significances of 18 alpha>(*) over bar * (H)- neohopanes and of 17 alpha>(*) over bar * (H)-diahopanes in oils from west Xialiaohe depression of the Bohai Bay Basin have been studied. Relative abu ndance of 18 alpha>(*) over bar * (H)-neohopanes and of 17 alpha>(*) over b ar * (H)-diahopanes can be effectively used as maturity parameters, in a ra nge of medium-high mature stage, based on consideration on sedimentary-orga nic facies of source rocks. With a dual geochemical significance of maturit y and sedimentary-organic facies, neohopane and diahopane parameters can be well used in oil-source correlation and in petroleum population division. Formation, primary concentration and preservation of precursors of rearrang ed hopanes are closely related to depositional conditions such as Eh-pH and clays content. A series of probable diahopanes (series D) was detected in the oils, which exhibits a similar distribution pattern and geochemical beh avior as that of 17 alpha>(*) over bar * (H)-diahopanes (series B).