四川盆地页岩气富集控制因素及类型

Controlling factors and types of shale gas enrichment in the Sichuan Basin

四川盆地页岩气具有多领域、多层系、多类型的特点。有利的沉积相、成熟度和保存条件是四川盆地页岩气富集的关键因素。海相深水陆棚优质页岩具有源、储、可压一体页岩气的富集条件，为最有利的沉积相类型。湖相碳酸盐湖坡风暴滩沉积的页岩与灰岩互层组合，具有源、储、可压近配页岩气富集条件，有利于微裂缝的发育，具有较好储渗性。适中的成熟度（2％～3％）生气高峰阶段，饱和气有机孔隙最发育，页岩的储集性最好。在埋藏条件下，页岩气的赋存总体上随着埋深增加，吸附气缓慢下降，而游离气则较快增加，超压区有利于游离气保存。在此研究基础上，将四川盆地页岩气划分为3个层系5种类型。其中，下志留统盆内缘超压和盆内超高压深水陆棚厚层页岩气型最有利于页岩气富集。依据各层系有利的沉积相带，适中演化程度（镜质体反射率1．3％～3．5％），压力系数大于1．2，埋深小于4500m分布区，预测出不同层系的页岩气有利区。

Shale gas in the Sichuan Basin features in multi-domain, multi-layer and multi-types. The main controlling fac- tors for shale gas accumulation are favorable sedimentary facies, thermal maturity and preservation condition. High quality marine shale of deep shelf facies is high in hydrocarbon source quality, reservoir quality and fracturability, thus is the most favorable sedimentary facies. Sequences of carbonate lake slope storm beach facies consist of interbedded shale and limestone. The close combination of shale with high hydrocarbon source quality and limestone with high reservoir quality and high fracturability provides favorable conditions for shale gas accumulation. Shale with moderate thermal maturity （2 % -3 % ） for peak gas generation has the most developed gas-saturated organic pores, thus the best storage capacity. Shale gas content generally increases with increasing buried depth under burial conditions. The adsorbed gas content de- creases slowly,while the free gas content increase rapidly. Overpressure zone is favorable to free gas preservation. On this basis, gas shales in the Sichuan Basin can be divided facies with ultrahigh pressure within the Late Silurian into three layer series and five types. The thick shale of deep shelf basin and that with overpressure at the inner edge of the basin are the most favorable for shale gas enrichment. Favorable areas of shale gas in different layer series were predicted according to the criteria of favorable sedimentary facies zones, moderate thermal maturity （ Ro = 1.3 % - 3.5 % ） , pressure coeffi- cient over 1.2 and buried depth less than 4 500 m.