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储层致密期与天然气充注期的关系是致密砂岩气成藏机理及富集规律研究中尚未得到很好解决的关键问题。主要基于对四川盆地元坝—通南巴地区须家河组致密砂岩成岩演化史、天然气充注历史和致密砂岩储层有机—无机水岩相互作用序列的分析,总结了四川盆地元坝—通南巴地区须家河组致密砂岩储层致密化机理,厘定了储层致密期与天然气成藏期的关系。指出早期强的压实作用使储层物性大幅降低及其导致的半封闭—封闭成岩流体系统是致密储层形成的主要原因。后期半封闭—封闭成岩流体系统中,流体流通不畅,溶蚀作用产物迁移受阻,以就地沉淀形成胶结物为主,堵塞溶蚀孔隙和剩余原生孔隙,溶蚀作用越强胶结物含量也越高,从而使储层进一步致密化。须家河组烃源岩生排烃史和储层流体包裹体特征研究表明,天然气的充注发生在中侏罗世—早白垩世,以早白垩世为主。综合储层致密史、天然气充注史和有机—无机水岩相互作用序列分析认为天然气充注时储层已经致密,具有储层先致密天然气后成藏的特征。
The relationship between the tight period of the reservoir and the filling period of natural gas is a key issue which has not been well solved in the research on the mechanism of formation and enrichment of tight sandstone gas. Based on the analysis of the diagenetic evolution history of tight sandstone, filling history of natural gas and the organic-inorganic water-rock interaction in the tight sandstone of the Yuanjiahe Formation in the Yuanba-Tongnanba area in the Sichuan Basin, Densification mechanism of tight sandstone reservoirs in Xujiahe Formation in Nanba area, and the relationship between reservoir densification period and gas accumulation period was determined. It is pointed out that the early strong compaction reduces the reservoir physical properties and the resulting semi-closed-closed diagenetic fluid system is the main reason for the formation of tight reservoirs. In the late semi-closed-closed diagenetic fluid system, the fluid flow is poor, and the migration of dissolution products is hindered, cement is formed mainly by in-situ precipitation, and the dissolution pores and residual primary pores are blocked. The higher the dissolution is, Thus further densifying the reservoir. The hydrocarbon generation and expulsion history of the source rocks in the Xujiahe Formation and the characteristics of fluid inclusions in reservoirs show that the filling of natural gas occurred during the Middle Jurassic to the Early Cretaceous and dominated by the Early Cretaceous. The integrated reservoir tight history, natural gas charge history and organic-inorganic water-rock interaction sequence analysis suggest that the reservoirs are dense during filling of natural gas and have the characteristics of reservoirs that were formed after tight natural gas.