川西新场地区须二段深层致密砂岩储层类型与差异控储作用

Types of the deep tight sandstone reservoirs and their different controlling in the second member of Xujiahe Formation in Xinchang area,western Sichuan Basin

随着油气勘探向深部拓展,深层致密砂岩气已成为当前重要的勘探领域,但其储层非均质性强,相对优质储层分布规律不清为致密砂岩气的规模有效开发带来较大困难。以川西新场地区须二段深层气藏为例,以岩心观察、薄片鉴定、物性测试等分析测试为手段,系统开展了深层致密砂岩储层的岩石学、储集性能、成岩作用与构造破裂作用研究,进一步明确了相对优质储层类型及差异控储作用。研究表明:新场地区须二段致密砂岩储层可划分为极致密储层、裂缝型、孔隙型和孔隙—裂缝型4种储层类型,其中孔隙型、孔隙—裂缝型为有效储层类型。致密砂岩储层的形成与沉积环境、粒度、成岩及构造破裂作用关系密切,不同类型储层之间差异控储作用明显。总体上,沉积是基础、差异成岩与构造破裂作用是关键。其中,极致密储层可形成于不同的沉积环境,但相对细粒及富岩屑类砂岩为其形成的物质基础,强烈的压实与胶结作用是其孔隙不发育的主要因素,裂缝型储层则是极致密储层的基础上叠加了构造破裂作用;孔隙型储层主要形成于相对高能水下分流河道、河口坝,岩性以富含长石的中粗粒砂岩为主,溶蚀与绿泥石衬垫胶结作用是其孔隙形成的关键,相控作用明显,而孔隙—裂缝型储层则是在孔隙型储层基础叠加了构造破裂作用,具有“相断”双控性。

With the development of deep exploration,deep tight sandstone gas has become an important explora⁃tion field.However,it is difficult to develop on a large scale because of the unclear distribution of the relatively high-quality reservoirs.In this paper,the petrology,reservoir properties,diagenesis and structural fracturing of the deep tight sandstone reservoirs are systematically studied based on the second member of Xujiahe Formation(T3x2)in Xinchang area,and the types of relatively high-quality reservoirs and their controlling differences are further clarified.According to the matching relationship between pores and fractures,the tight sandstone reser⁃voirs of the T3x2 in Xinchang area can be divided into four types:extremely tight reservoir,fractured,porous,and pore-fractured types.Among them,the porous and pore-fractured reservoirs are effective reservoirs.The formation of tight sandstone reservoirs is closely related to their sedimentary environments,grain sizes,diagene⁃sis,and tectonic fracturing,with significant controlling differences between different reservoirs.Overall,sedi⁃mentation is the foundation,and differential diagenesis and tectonic fracturing are the key factors.Among them,extremely tight reservoir can be formed in different sedimentary microfacies,with relatively fine-grained and rich-lithic sandstones as the basis for their formation,and strong compaction and cementation are the main fac⁃tors for the underdevelopment of their pores.However,fractured-type reservoirs are mainly formed on the basis of extremely tight reservoir superimposed by tectonic fracturing.Porous reservoirs are mainly formed in relative⁃ly high-energy distributary channels and mouth bars.And the reservoir lithology is mainly composed of medium to coarse-grained sandstone rich in feldspar.Dissolution and chlorite-liner cementation are the key factors for their pore formation.However,the pore-fractured reservoirs are formed on the basis of porous reservoirs super⁃imposed by tectonic fracturing.