川西坳陷中三叠统雷口坡组天然气气源对比

川西坳陷中三叠统雷口坡组是近年来四川盆地海相天然气勘探和研究的热点层系,目前对其碳酸盐岩生烃潜力的认识存在一定分歧,由此导致该地区雷口坡组气藏的主力气源存在较大争议。通过对川西坳陷潜在海相烃源岩开展较为系统的地球化学分析,揭示了雷口坡组碳酸盐岩和筇竹寺组、龙潭组、马鞍塘组—小塘子组泥质烃源岩的有机质丰度、类型、成熟度和生烃潜量等特征。其中,雷口坡组碳酸盐岩的原始有机质丰度和生烃潜量整体偏低,有机质丰度相对高的层段发育规模十分有限,不足以形成规模性油气聚集,且雷口坡组高产井与其碳酸盐岩烃源岩的发育程度明显不匹配。气源对比研究表明,雷口坡组天然气主要来自下伏上二叠统龙潭组烃源岩,与下寒武统筇竹寺组或上三叠统马鞍塘组—小塘子组烃源岩不具有亲缘性。雷口坡组储层未经历大规模古油藏聚集,其气藏为龙潭组烃源岩所生成的原油在高演化阶段热裂解生成原油裂解气并直接充注到雷口坡组而形成。

Gas-source correlation of natural gas in the Middle Triassic Leikoupo Formation in the western Sichuan depression

In recent years, the Middle Triassic Leikoupo Formation in the western Sichuan depression has become a hotspot of exploration and study of marine gas in Sichuan Basin. There are some differences in the understanding of the hydrocarbon potential of carbonate rocks, resulting in great disputes on the main gas-source of gas reservoirs in Leikoupo Formation. Through the systematic geochemical analysis of potential marine source rocks in the western Sichuan depression, this paper reveals the organic matter abundance, type, maturity and genetic potential and other characteristics of carbonate rocks in Leikoupo Formation and argillaceous source rocks in Qiongzhusi Formation, Longtan Formation, Ma'antang Formation, and Xiaotangzi Formation. The original organic abundance and hydrocarbon potential of carbonate rocks in Leikoupo Formation are generally low, and the sections with relatively high organic matter abundance are developed on a limited scale, not enough to form large-scale oil and gas accumulation. Moreover, the high productivity of wells in Leikoupo Formation obviously does not match with the development degree of carbonate source rocks. The gas-source correlation shows that the gas in Leikoupo Formation was mainly generated from the source rocks of the Upper Permian Longtan Formation, with no affinity for the source rocks of the Upper Cambrian Qiongzhusi Formation or the Upper Triassic Ma'antang Formation-Xiaotangzi Formation. Leikoupo Formation has not experienced large-scale accumulation of paleo-reservoir. The Leikoupo Formation is directly charged by the oil cracking gas formed by cracking of the crude oil generated from the source rocks of Longtan Formation in the high evolution stage, thus forming the gas reservoirs.