Sequential extraction and compositional analysis of oil-bearing fluid inclusions in reservoir rocks from Kuche Depression, Tarim Basin

The free oils, adsorbed oils and oil-bearing fluid inclusions have been ext racted separately and analyzed by GC and GC-MS in reservoir rock samples co llected from the Kuche Depression. The results demonstrate that the molecul ar compositions of oil-bearing fluid inclusions are significantly different from those of the free oils (the current oils). Compared with the current oil, the oil-bearing fluid inclusions are characterized by relatively high values of parameters Pr/nC(17) and Ph/nC(18), low values of Pr/Ph, hopanes/ steranes, C-30-diahopane/C-30-hopane and Ts/Tm, low content of C29Ts terpan e and high maturities as indicated by C-29 steranes 20S/(20R+20S). In addit ion, the oil-bearing fluid inclusions correlate very well with the oils in northern and central Tarim Basin, which were derived from Cambrian-Ordovici an marine source rocks. The adsorbed oils appear to be an intermediate type between free oils and oil-bearing fluid inclusions. The above analytical d ata indicate that there are at least two oil-charging episodes for these re servoir rock samples. The early charging oils were derived from Cambrian-Or dovician marine source rocks, and the later charging oils, from Triassic-Ju rassic terrestrial source rocks. The primary marine oils were overwhelmingl y diluted by the following terrestrial oils.