川西坳陷须家河组天然气成藏模式探讨

Gas reservoiring mode in Xujiahe Formation of western Sichuan depression

川西坳陷须家河组可分为下部成藏组合和上部成藏组合。下部成藏组合主要有高压驱赶、低压吸拉天然气成藏模式;上部成藏组合主要有水溶气运移释放、浮力顺优势通道输导天然气成藏模式。早期古构造之上叠加晚期“断而未破”的裂缝系统是高压驱赶天然气成藏模式富集高产的主控因素;充足的天然气源、开启的断裂、挤压构造的虚脱及地层剥蚀减压是低压吸拉天然气成藏模式成藏的关键;构造高点曾不断迁移变化、晚期抬升、储层物性较好的低幅度构造+岩性复合圈闭是水溶气运移释放天然气成藏模式的决定因素;优势运移通道上存在的有效圈闭是浮力顺优势通道输导天然气成藏模式成藏的关键。

Xujiahe Formation can be divided into a lower and an upper reservoir assemblages Pooling modes for the former are thought to be high-pressure drive and low-pressure suction and pull and that for the later are regarded as water-soluble gas migration and release and buoyancy transmitting gas through dominant pathway. For the high pressure drive mode, the controlling factor of gas enrichment is the existence of faulted but unbroken＇ fracture system superimposed on the early palaeostructure, and for the low-pressure suction and pull mode, the key factors of gas pooling include sufficient gas source, open faults, compressional structure suction, and decompression by stratum denudation. For the water-soluble gas migration and release mode, the determining elements of gas reservoiring are the continuous migration of structural high, late uplift, and low relief structural and lithologic combination trap with good physical properties; for the mode of buoyancy transmitting gas through dominant pathway, the crucial condition for gas reservoiring is the existence of effective traps on dominant pathway.