川中—川西须家河组三段致密砂岩储集层分类及成因

Classification and origin of tight sandstone reservoirs of the 3rd Member of Xujiahe Formation in central and western Sichuan Basin

四川盆地中部和西部(川中—川西)上三叠统须家河组岩石组分复杂、孔喉结构非均质强,含气和产能平面变化快,亟需明确储集层分类标准、发育机制及分布规律。以须家河组三段致密砂岩为对象,通过薄片、物性、压汞和核磁共振等实验,分析微观孔隙结构,建立储集层分类评价标准,揭示岩石组分、成岩作用对储集层类型的控制。研究表明,须三段发育微裂缝、原生粒间孔、残留粒间孔、溶蚀孔和晶间孔5类储集空间,粒间孔喉发育程度是决定储集层品质的关键;基于分形特征,将孔喉系统划分为5个区间,结合中大孔喉占比、主流喉道等参数,实现4类致密储集层的精细划分;I类储集层具有“弱压实强溶蚀”特征,高石英颗粒、低泥岩和碳酸盐岩岩屑、适量火山岩岩屑是形成的关键,Ⅱ类储集层具有“强压实强溶蚀”特征,较多杂基、低泥岩岩屑、高长石颗粒是形成的物质基础,Ⅲ类和Ⅳ类储集层均具有强胶结特征,其中Ⅲ类储集层中钙质岩屑含量高,方解石胶结发育,Ⅳ类储集层杂基减孔明显。研究成果可指导该区致密储集层形成机制研究,也为致密储集层分类和成因关联分析提供一定借鉴。

Due to the complex rock composition and strong heterogeneity in pore throat structure of the Upper Triassic Xujiahe Formation in central and western Sichuan Basin,the gas content and produc-tivity show rapid changes.Therefore,it is urgent to clarify the reservoir types,formation mechanisms,and their distribution characterization.Taking the tight sandstone reservoirs of the 3rd Member of the Xujia-he Formation as the object,this study conducts microscopic analysis of pore structure through thin section,physical properties,mercury intrusion,and nuclear magnetic resonance,establishes reservoir classifica-tion standards,and then reveals the control of diagenesis and rock composition on the formation of various reservoir types.The results show that there are five types of reservoir spaces developed in the 3rd Member of the Xujiahe Formation,including microcracks,primary intergranular pores,residual intergranular pores,dissolution pores,and intercrystalline pores,among which the development of the intergranular pore throats is the key to reservoir quality.Based on the fractal features,the pore throat system is divided into five intervals,and combined with parameters such as the proportion of meso to macro pore throats and main flow throat radius,four types of tight reservoirs are finely divided.TypeⅠreservoirs feature“weak compaction and strong dissolution”,which is related to high percentage of quartz particles,low percen-tage of mudstone and carbonate rock fragments,and moderate volcanic rock debris;TypeⅡreservoirs ex-hibit“strong compaction and strong dissolution”,with a large amount of impurities,low percentage of mudstone debris,and high percentage of feldspar particles as the material basis for their formation;Both TypeⅢand TypeⅣreservoirs have strong cementation characteristics,calcite cementation was developed due to the high content of calcareous rock debris in TypeⅢreservoirs,while significant reduction of pore size related to the matrix in TypeⅣreservoirs.This research can not only guide the study of the formation mechanism of tight reservoirs in the study area,but also provide certain reference for the correlation be-tween the classification and genetic of tight reservoirs.