四川盆地天然气成藏动力学初探

PRIMARY STUDY ON THE DYNAMICS OF NATURAL GASPOOLS IN SICHUAN BASIN, CHINA

四川叠合盆地是我国主要的天然气区之一。天然气成藏动力学是今后四川盆地天然气地质和勘探研究的重要内容。可将川西地区上三叠统须家河组视为一个完整的含气高压封存箱。川东地区在纵向剖面上存在两个压力封存箱,第一个压力异常带(下三叠统嘉陵江组—二叠系)为上部流体高压封存箱,第二个高压异常带(志留系)为下部流体高压封存箱,石炭系位于两个压力封存箱之间。生烃增压为上列封存箱内主要的升压机制。川西地区致密碎屑岩储层和川东地区碳酸盐岩储层初次运移排烃方式主要为垂向排烃,并且是在异常古高压驱使下通过封存箱破裂产生的混相涌流完成的。异常古高压是促使川西地区须家河组须二段和须四段储层流体调整并使天然气聚集成藏的动力。浮力和水动力(成藏动力)控制了川东地区天然气的成藏。

Sichuan superposition basin is one of the main natural gas production areas in China. The dynamics of natural gas pools is the critical studying content about the natural gas exploration in the basin. The upper Triassic Xujiahe formation in west Sichuan basin can be thought as an entire abnormal pressured compartment with natural gas. There are two abnormal pressured fluid compartments in vertical profiles of east Sichuan basin. The first one, called upper abnormal pressured fluid compartment, is located from lower Triassic Jialingjiang formation to Permian system. The second one, called lower abnormal pressured fluid compartment, is located in Silurian system. Carboniferous system is in the middle of the two abnormal pressured fluid compartments. Hydrocarbon-generation is the chief lifting pressure mechanism within compartments. The model of initial migration and expulsion is vertical in the tight clastic reservoir of west Sichuan basin and the carbonate reservoir of east Sichuan basin. The mode is made by the abnormal paleo-overpressure through the crack of abnormal pressured fluid compartments. The abnormal paleo-overpressure was the movement force, which made the adjustment of the fluids and the formation of natural gas reservoir pools within the upper Triassic Xujiahe formation. Buoyancy and hydrodynamics has controlled the formation of the natural gas reservoir pools in east Sichuan basin.