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

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.