四川盆地天府含气区侏罗系沙溪庙组一段致密砂岩储层特征及主控因素

Characteristics and main controlling factors of tight sandstone reservoir in the first member of Jurassic Shaximiao Formation in Tianfu gas-bearing area,Sichuan Basin

四川盆地中部地区是中国致密气勘探开发的重点地区,复杂的砂体分布以及优质储层的形成机制和分布规律是制约该地区天然气勘探开发的关键科学问题。基于岩石学、铸体薄片、物性测试及高压压汞等方法,综合研究天府含气区沙溪庙组一段储层岩石类型、储集物性、储集空间及成岩作用,并据此分析储层主控因素。结果表明:研究区沙溪庙组一段致密砂岩储层主要发育在中—粗粒岩屑长石砂岩及长石岩屑砂岩中,储集空间以原生粒间孔为主,其次为长石、浊沸石溶孔,喉道多呈片状及缩颈型喉道。沙溪庙组致密砂岩储层受沉积作用、物质组成及成岩作用共同制约,其中高能稳定的沉积相是形成优质储层的先决条件,长石含量决定了储层整体溶蚀孔隙发育程度,岩屑类型的不同导致后期差异成岩作用的产生。绿泥石包壳及早期形成的胶结物抵抗压实作用使原生孔隙得以保存,长石及早期浊沸石的溶蚀成为储层物性改善的关键,而晚期的浊沸石和方解石胶结是导致储层被破坏的主要因素。

As a key area for tight gas exploration and development in China,the complex distribution of sands as well as the formation mechanism and distribution law of high-quality reservoirs in the central Sichuan area are scientific issues that determine the exploration and development of natural gas in the area.Based on petrography,casting thin section,physical property test,high pressure mercury pressure and other methods,we comprehensively studied the rock type,reservoir properties,reservoir space,and petrogenesis of the Shaximiao Formation reservoir in the Tianfu gas-bearing area,and analyzed the main controlling factors of the reservoir accordingly.The results show that the dense sandstone reservoirs in the Shaximiao Formation are mainly developed in medium-coarse grained feldspathic sandstone and feldspathic sandstone,with primary intergranular pores dominating the reservoir space,followed by feldspathic and turbidite zeolite dissolution pores,and most of the throats are lamellar and necking-type throats.The dense sandstone reservoirs of the Shaximiao Formation are governed by sedimentation,material composition and diagenesis,in which a high-energy and stable sedimentary phase is a prerequisite for the formation of high-quality reservoirs,the feldspar content determines the degree of the overall development of dissolution pores in the reservoirs,and the differences in the types of rock clasts lead to the generation of different diagenesis in the later stages of the formation of different rock clasts.The chlorite crust and early cement resisted the compaction to preserve the primary pores,feldspar and early turbidite dissolution were the key to improve the physical properties of the reservoir,while the late turbidite and calcite cementation was the main factor leading to the destruction of the reservoir.