Geochemical evidence for the recognition of the Carboniferous condensate by evaporative fractionation from Tabei Sha-18 Well

摘要

The conventional understanding of condensate is that almost all condensates derived from sapropelic kerogen are the product of highly matured organic matter (R_0>1.3%) during the late stage of diagenesis or of thermally cracking of high molecular weight hydrocarbons during the early stage of diagenesis. Recent studies indicate that the petroleum evaporative fractionation, although to which little attention has been paid, is objectively a significant and frequently occurring mechanism for petroleum alteration and condensate generation. Our research has shown that there are a certain number of favorably geological and geochemical factors in the Tarim Basin for the occurrence of petroleum evaporative fractionation and the generation of corresponding condensates and residual oils. In this note, the marine Carboniferous condensate of Sha-18 Well and related marine Ordovician high-wax oil of Sha-14 Well were selected for detailed discussion. Sha-18 and Sha-14 Wells are located in the central part of theSangtamu fault block. The fact that a string of gas and oil reserviors have been discovered along this block reveals that the faults on both sides could be pathway for the occurrence of petroleum evaporative fractionation.