天然气充注成藏与深部砂岩储集层的形成 ——以塔里木盆地库车坳陷为例

在塔里木盆地库车坳陷深层天然气成藏条件分析的基础上,阐明深部有效储集层的形成机制.研究表明,天然气充注成藏过程与深部砂岩有效储集层的形成具有密切关系:早期曾捕获到油气的储集层,后期深埋后储集层性能较好;若早期未能捕获到油气,深埋后储集层则比较致密.深埋压实作用对孔、缝的保存影响较大.在储集层深埋致密化之前发生的油气充注过程,抑制了岩石的机械压实和裂缝闭合,阻碍了致密化进程,使储集层的有效孔、缝得以保存.库车深层煤系气源充沛,高演化侏罗系烃源岩成气潜力依然较大,深部砂岩储集层发育次生孔隙和微裂隙,膏盐盖层分布广,厚度大,生储盖空间配置好;以断裂为主构成的输导体系发育,排烃效率高,运聚系数大,油气被高效捕获成藏;盐构造下的深部和超深部圈闭发育.因而,库车坳陷深层和超深层成藏条件好,勘探潜力巨大.

Coupling relationship between natural gas charging and deep sandstone reservoir formation: A case from the Kuqa Depression, Tarim Basin

The formation mechanism of deep effective reservoirs is elaborated based on the analysis of the conditions for forming natural gas accumulations in deep Kuqa Depression. Natural gas charging is closely related to the formation of effective sandstone reservoirs in the deep zone: reservoirs which capture oil and gas in the early period are of better quality during the long burial period; reservoirs which do not capture oil and gas in the early period is compact after deep burial because of compaction. Oil and gas charging before the reservoir is deeply buried significantly inhibits mechanical compaction and fracture closure as well as densification, so the effective pores and fractures will be preserved. The formation conditions of large gas fields in Kuqa Depression are as follows: sufficient coal gas source; great gas generation potential of high-evolution Jurassic source rocks; secondary pores and micro-fissures developed in deep sandstone reservoirs; wide distribution of gypsum-salt cap rock with large thickness; good association of source-reservoir-cap in space; well developed hydrocarbon migration pathways of dominantly faults; high expulsion efficiency; big migration and accumulation coefficient and deep or ultra-deep traps developed below salt structures.