龙门山南段前陆冲断带内的古油气藏

Ancient oil and gas reservoir in the foreland thrust belt of south section of Longmenshan Mountains,China

通过对龙门山南段地表沥青发育特征及分布规律的研究,对比不同层位中流体充注特征,结合该地区构造演化史,证实了龙门山南段冲断带内曾经存在过古油(气)藏,重塑了古油(气)藏形成和破坏的过程。研究表明,沥青主要分布于观雾山组和灯影组次生溶孔、溶洞和裂缝中;以灯影组中沥青最为发育,侧向延伸稳定,垂向充填较厚,说明研究区曾存在过古油(气)藏。晚三叠世以前,来源于松潘-甘孜海盆的油藏流体,由西向东运移充注于现今前陆冲断带内的震旦系灯影组、泥盆系和二叠系储集空间中形成古油藏;晚三叠世盆山转换时期,古油藏随着前陆盆地的快速沉降而被深埋,油裂解成气而形成古气藏;随着冲断带向前陆盆地扩展,赋存于前陆盆地内的古气藏被破坏。

Based on the study of the development and distribution of bitumen outcrops, filling characteristics of fluids in different layers and tectonic deformation, an ancient oil and gas reservoir can be identified in the south section of Longmenshan Mountains, and the process of development and destruction of the ancient oil and gas reservoir is reconstructed. The research indicates that there is a great lot of bitumen to fill in the secondary rugs and fissures in the Devonian Guangwushan Formation and Sinian Dengying Formation. The abundant bitumen, stable extension and great thickness of bitumen infilling in Dengying Formation suggest that there is an ancient oil and gas reservoir in the south section of Longmenshan Mountains. The hydrocarbon from the Songpan-Ganzi ocean basin migrated from west to east and filled into Dengying Formation, Guanwushan Formation and Permian located in the foreland thrust belt to form the ancient oil reservoir before Late Triassic. With the Songpan-Ganzi ocean basin transformed to orogenic belt and the foreland basin developing in Late Triassic, the ancient oil reservoir was deeply buried and cracked to form the ancient gas reservoir. The gas reservoir was destroyed further during the foreland thrust belt progressed and migrated from orogenic belt to foreland basin.