川东地区志留系-石炭系含气系统天然气运移聚集机理

根据川东地区石炭系、志留系天然气藏的形成与分布特点,结合地层压力分布特征,探讨了该区志留系-石炭系含气系统的天然气运移聚集机理,提出该系统具有箱外成藏和箱内成藏两种模式。下伏志留系高压封存箱生成的油气随箱体顶部破裂呈混相涌流进入石炭系,油气在石炭系中向继承性发育的古隆起运移聚集,形成大型古油气藏,后逐渐演化成古气藏。志留系封存箱内部的天然气可在有利储集层中聚集成藏。喜山构造运动使研究区天然气重新大规模运移聚集,形成充满度很高的残余气藏。石炭系储层气驱水实验表明,岩石渗透率与驱替后残余水饱和度呈负相关指数关系。在一般地层压力条件下,天然气很难通过岩层的细小孔隙运移并排替地层水富集,细小孔隙中的天然气是早期聚集其中的。水溶对流可能是石炭系天然气运聚成藏的重要机制。

MIGRATION AND ACCUMULATION MECHANISM OF NATURAL GAS IN THE SILURIAN-CARBONIFEROUS PETROLEUM SYSTEM OF EAST PART IN SICHUAN BASIN

Based on the characteristics of natural gas generation and distribution as well as the that of formation pressures in the east part of Sichuan Basin,migration and accumulation mechanism of natural gas in Silurian Carboniferous petroleum system in the area is studied in the paper. There are two kinds of model for forming gas pools both in the abnormally pressured compartment and out the compartment in the system.After the breakage of overpressured fluid compartments in Silurian system,hydrocarbons generated in the compartments flowed to Carboniferous in a phase of mixed fluids. Within Carboniferous system,hydrocarbons migrated to the crest part of the existed uplift traps and formed primary oil and gas accumulation which then were changed into gas pools with their further buring. A large scale migration and accumulation took place during Later Himalayan movement,as a result a type of called remained gas pools with higher gas columns were formed. The water displacement experiment of Carboniferous gas showed that under normal pressure natural gas in subsurface reservoir is difficult to migrate into minor pores and displaced water out the pores in reservoir. Obviously this kind of gas reserved in minor pores migrated in early stage. The dissolution convection may be an important mechanism for the migration and accumulation of gas pools.