青海南部冻土区二叠系那益雄组天然气水合物烃源岩评价

青海南部开心岭-乌丽冻土区是青藏高原天然气水合物赋存的有利地区,该区二叠系那益雄组的烃源岩是形成天然气水合物的重要气体来源。为系统评价该地层烃源岩特征,对研究区钻井岩心泥岩样品进行了有机地球化学分析。结果表明,研究区烃源岩有机质含量较高,有机质成熟度为高-过成熟,且干酪根类型以II型为主。由于所测岩样现今埋深均较浅,长期的风化、淋滤作用导致实验测定的残余有机质丰度偏低,需要进行有机质丰度恢复以重新评价。综合分析认为,该区二叠纪那益雄组烃源岩达到了好的烃源岩评价标准。此外,该烃源岩在演化过程中已经产生并排出了大量的烃,且目前处于干气大量产生的阶段,被深大断裂导通的深部烃源岩可为天然气水合物的形成提供重要的气源。

The evaluation on source rocks for natural gas hydrate in Permian Nayixiong Formation of southern Qinghai permafrost

The Kaixinling-Wuli permafrost of southern Qinghai is a favorable region for natural gas hydrate, whose gas sources are significantly fed by source rocks of Permian Nayixiong Formation. In order to assess the characteristics of these source rocks comprehensively, organic geochemical analyses have been carried out on the mudstone samples collected from several boreholes. The results show high organic matter contents in these sources rocks with high to over-maturity and kerogen type II in majority. All the measured samples are buried at shallow depths at present, which have been subjected to long-term weathering and leaching and depleted in the residual content of organic matter, so a reevaluation is made after the restoration of organic matter abundance. A conclusive result is that the source rocks of Nayixiong Formation could reach the good evaluation criterion. In addition, it is concluded that large volume of hydrocarbon had been expulsed during the thermal evolution process and now the source rocks have reached to their stages of dry gas expulsion, so these deep-buried source rocks could serve as favorable gas-source for natural gas hydrate formation if connected by deep faults.