中国南方典型页岩孔隙特征差异及其控制因素

Characteristic differences and controlling factors of pores in typical South China shale

深入分析不同沉积背景页岩储层物质基础、探究不同层系页岩储层发育主控因素是预测页岩气藏地质甜点的核心工作。中国南方海相页岩气已实现大规模商业开发,而海-陆过渡相和陆相页岩气勘探鲜有突破。选取川西南海相页岩、湘中海-陆过渡相页岩和川东北陆相页岩为研究对象,在沉积背景、地化特征、岩石学特征以及孔隙结构特征研究的基础上,通过对比多层系页岩储层特征,明确了不同层系页岩储集能力主控因素。研究表明:海相页岩发育Ⅰ型有机质具迁移和产孔能力,以有机质孔隙为主,优势岩相为富有机质硅质页岩,具有高孔体积(平均值0.026 cm^3/g)和高比表面积(平均值28.99 m^2/g)特征,有机质丰度是储集能力好坏的决定性因素;海-陆过渡相发育Ⅲ型有机质呈惰性,以粘土矿物孔隙为主,优势岩相为富含有机质泥质页岩,具有高孔体积(平均值0.023 cm^3/g)和低比表面积(平均值6.33 m^2/g)特征,合理的矿物组构匹配(硅泥比2/3)是储集能力好坏的决定性因素;陆相有机质显微组分混杂,以粘土矿物孔隙和有机质孔隙为主,优势岩相为富有机质泥质页岩和富有机质混合质页岩,孔体积(平均值0.017 cm^3/g)和比表面积(平均值11.90 m^2/g)适中,高腐泥质含量(大于60%)和合理的矿物组构匹配是储集能力优越的有利条件。不同沉积背景页岩物质基础在差异成岩改造作用下呈现出迥异的储集性能,勘探目标应依据特定页岩层系差别对待。

Sweet spot prediction in shale usually depends on a general evaluation of hydrocarbon potential of reservoirs against various sedimentary settings and a thorough investigation into the main controlling factors on reservoir development in different strata context.Despite a large-scale commercial development of shale gas in South China,the marine-continental transitional shale and continental shale in the region have not contributed much to the boom so far.To turn the scale,representative shales in southeastern(marine)and northeastern(continental)Sichuan Basin as well as central Hunan Province(transitional),were sampled and analyzed in their respective sedimentary settings,geochemical attributes,petrological features and pore structure characteristics,to clarify the major factors controlling the reservoir capacity.The results show that marine shale with Type Ⅰ maceral from southeastern Sichuan Basin is transportable and potentially porous with organic matter pores.The most promising facies is the organic-rich siliceous shale characterized by high pore volume(PV)(0.026 cm^3/g on average)and high specific surface area(SSA)(28.99 m^2/g on average)and with the abundance of organic matter determining the storage capacity.The marine-continental transitional shale with Type Ⅲ maceral of inertia from the central Hunan Province is dominated by clay mineral pores.The most promising facies is organic-rich clay characterized by high PV(0.023 cm^3/g on average)and low SSA(6.33 m^2/g on average)and with Si/Al ratios(ideally 2/3)controlling the reservoir capacity.The continental shale with mixing organic matter macerals from the northeastern Sichuan Basin is dominated by clay minerals and organic matter pores.The most promising facies is organic-rich clay mixed with shale,characterized by medium PV(0.017 cm^3/g on average)and SSA(11.90 m^2/g on average)and with both sapropelic content(>60%)and mineral ratios controlling the reservoir capacity.In all,shales with different sedimentary settings and under differential diagenetic modification present distinctive reservoir properties that require tailor-made exploration strategy.