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. 中国西部发现的大量天然气多具有干酪根降解和原油裂解两种裂解气特征，选择有机质丰度高、成熟度低的新疆三塘湖盆地二叠系灰岩样品和川东北地区飞仙关组灰岩抽提油样，设计并完成了有机质成油、成气和油成气模拟实验，以考察这两种裂解气气源生气史和其对气藏的贡献。根据热模拟实验结果建立并标定了干酪根生油、生气及油成气的化学动力学模型，并运用该模型评价了川东北地区二叠系烃源岩生油史、生气史及三叠系飞仙关组古油藏裂解成气史。研究结果表明，川东北地区二叠系烃源岩主要生油时期为距今210～190 Ma，主要生气期为距今205～185 Ma（印支晚期），三叠系飞仙关组油裂解生气主要时期为距今165～150 Ma。根据两种裂解气的生气史，初步估算了两种裂解气的相对贡献，其中干酪根生气和油裂解生气相对比例分别为17%和83%。