Lu Shuangfang

Oil generation threshold depth of Songliao Basin: Revision and its significance

Abstract A systematic analysis was carried out on the relation curve of hydrocarbon transformation ratio vs. buried depth and that of vitrinite reflectance (Ro) vs. buried depth in Binbei area, major source rock area (Qijia-Gulong Sag and Sanzhao Sag), and major source rock layer (Cretaceous Qing-1 Member, Qing-2 – Qing-3 Members) in Songliao Basin, to re-determine the oil generation threshold depth of the basin. The oil generation threshold depth of the major source rocks is likely to range from 1400 m to 1700 m, rather than 1 200 m in the previous estimation. The change of oil generation threshold has different effects on the resources potential and exploration orientation of various areas: For the major source rock areas, increase of oil generation threshold depth will cause decrease of oil generation and expulsion quantity, with no evident effect on the resources potential of major source rock area but with certain effect on the exploration orientation and favorable target evaluation. For the Binbei area with shallower buried depth of source rocks, it will have great effect on the exploration potential, exploration orientation, and favorable target evaluation. For the southeastern uplift area with great denudation in the basin, the oil generation threshold depth is reduced to about 700 m, which will improve the exploration potential of Chaoyanggou terrace, Changchunling anticline, and Binxian-Wangfu area.

Generation history of the two gas-sources of Feixianguan Formation gas-pools in the NE Sichuan Basin and their relative contribution

Abstract The natural gas produced in Feixianguan Formation in NE Sichuan Basin is characterized by kerogen cracking and oil cracking. Source rock samples were taken from the Permian limestone in Santanghu Basin, Xinjiang, with high organic matter abundance and low maturity, and oil samples from the Feixianguan limestone in the NE Sichuan area. Oil and gas generation simulation experiments were designed and carried out to appraise the gas generation history and the relative contribution of the two-type sources. Based on simulation results, the chemical kinetic models involving oil-gas generation were built and the kinetic parameters of each model were demarcated. The oil and gas generation history and the oil cracking history were studied with above mentioned models. The results show that major oil generation period of the Permian source rock is between 210 Ma and 190 Ma, the major gas generation period is between 205 Ma and 185 Ma, and the major gas generation period of oil cracking in Feixianguan Formation is between 165 Ma and 150 Ma. The contributions of gas from kerogen cracking and oil cracking were estimated based on the gas generation history and the source rock characteristics. The contributions of the two cracking gases are 17% and 83%, respectively.

Activity of bacteria and archaea in immature or lower-mature organic matter and new appraisal methods for biogas source rocks

Abstract The geochemical analyses of samples from both east Qaidam Basin and north Songliao Basin are implemented based on examining the influence of the activity of bacteria and archaea on the distribution of main biomarkers in saturated hydrocarbons and on the content of carbazole derivatives, with the aid of microbiological research results. Studies suggest that the regular sterane/17α (H) hopane value, C35αβ homohopane index, oleanane index, BNH/TNH ratio, and the abundance change of C28-C31 alkyl steranes can be used to appraise the activity of bacteria and archaea. In the strongly anaerobic environment from fresh water to saline water, the content of organic nitrogen in gas-generated materials is related to the nitrogen fixation of methanosarcina. Under the methane-producing condition, nitrogen-bearing heterocyclic compounds from protoplasm are degraded by methanogenesis partners. Thus, the contents of carbazole, methyl-carbazole and benzol-carbazole compounds are lower about 1 to 2 order of magnitude in excellent biogas source rocks than in other type samples.