Abstract:

Paleogene Shahejie Formation is investigated for its excellent shale oil potential in Jiyang depression, Bohai Bay Basin. The thickness of Shahejie Formation shale within the oil window reaches more than 1000 m and the characteristics of shale organic matter thermal evolution has attracted widespread interest. Based on the detailed statistics of the pyrolysis geochemical parameters for five exploration wells for shale oil， the analyses of original total organic carbon (TOCo) of a source rock, the convertible carbon (Cc), the oil in place from S1 and generation potential from S2 etc., the characteristics of the shale organic matter thermal evolution of Shahejie Formation has been studied, and the vitrinite reflectance kinetics of shale has also been discussed in this paper. The results suggest that Shahejie Formation shale（lower part of the 3rd and upper part of the 4th Member of Shahejie）is of particular exploration interest, which yields the maximum pyrolysis temperature (Tmax) values ranging from 423 ℃ to 450 ℃.The thermal maturity (Ro) values range from 0.45% to 0.94% with the average value of 0.73%, implying that it belongs to the mature oil window shale. Original total organic carbon (TOCo) values of a source rock of type II values range from 0.64% to 7.25%, and the average TOCo is 4.60%. Organic carbon converted to hydrocarbons is called convertible carbon (Cc), and its values range from 51% to 63%, with the average Cc value of 59%. The oil content of shale values range from 10×104 t/km2 to 75×104 t/km2, with average value of 39.67×104 t/km2. The hydrocarbon generating potential values range from 20×104 t/km2 to 465×104 t/km2, with average value of 293×104 t/km2. Pyrolysis production index (PI) (or S1/［S1+S2］) values range from 0.03 to 0.47. The comprehensive study reveals that the excellent source rocks of Shahejie Formation are concentrated in Dongying and Zhanhua sags, and the thermal maturity is significant for the generation and accumulation of shale oil. When the Ro values were at about 0.70%0.74% the expulsion of hydrocarbons began.

Key words: Paleogene, Shahejie Formation, Shale oil, Characteristics of thermal evolution, Jiyang depression