四川盆地西北部上二叠统吴家坪组火山碎屑岩孔隙演化特征及有利储集区分布

通过对大量岩心、薄片、扫描电镜、测井及物性等资料的研究，分析了四川盆地西北部上二叠统吴家坪组火山碎屑岩的岩石学特征、孔隙特征、孔隙成岩作用及其演化特征，并在此基础上预测了火山碎屑岩有利储层的分布。吴家坪组火山碎屑岩主要包括凝灰岩、沉凝灰岩、凝灰质泥岩及凝灰质粉砂岩等，主要分布于吴二段，吴一段、吴三段分布较少。由于受到脱玻化、溶蚀、胶结、交代及压实作用的影响，火山碎屑岩主要发育收缩孔、粒间溶孔、粒内溶孔。在早成岩阶段A期，脱玻化作用促使收缩孔的发育，从而增加了孔隙度；在早成岩阶段B期，胶结作用及压实作用导致孔隙度降低；进入中成岩阶段A期时，交代作用使孔隙度小幅度降低。火山碎屑岩的孔隙整体发育较好，火山碎屑岩储层厚1.3~60.9 m，储层总厚度变化较大，有利储集区主要集中在双鱼石—龙岗西地区，是研究区有利的勘探目标。

Pore evolution characteristics and distribution of favorable reservoir area of the Upper Permian Wujiaping Formation in the Northwestern Sichuan

Through the study of a large number of cores， slices， scanning electron microscopes， well logs and physical properties， the petrological characteristics， pore characteristics， pore diagenesis and evolution characteristics of the pyroclastic rocks of Wujiaping Formation in northwestern Sichuan were analyzed. On this basis， favorable reservoirs lithology distribution was studied. The pyroclastic rocks of Wujiaping Formation mainly include tuff， tuffite， tuff mudstone and tuff siltstone， etc.， which are mainly distributed in the Wu 2 Member， while the distribution of Wu 1 Member and Wu 3 Member is less. Due to the effects of devitrification， dissolution， cementation， replacement and compaction， pyroclastic rocks mainly develop shrinkage pores， intergranular dissolution pores， and intragranular dissolution pores. In the early diagenetic stage A， devitrification promotes the development of shrinkage pores， thereby increasing the porosity； in the early diagenetic stage B， cementation and compaction cause the porosity to decrease； when entering the mid-diagenetic stage A， the metasomatism reduces the porosity slightly. The porosity of pyroclastic rocks as a whole is characterized by high porosity， and thickness of layer of pyroclastic reservoir is from 1.3 m to 60.9 m. The total thickness of the reservoirs varies greatly. The favorable reservoir areas are mainly concentrated in Shuangyushi-Longgangxi areas， which is a favorable exploration target in the study area.