川西新场—丰谷地区须二段致密砂岩储层有效构造裂缝成因及发育规律OA

The tight sandstone reservoir in western Sichuan is characterized by a deep buried depth,strong heterogeneity,and a high degree of densification.This large-scale structural fracture system has an important influence on the efficient exploration and development of tight gas.However,the controlling factors and distribution law of the effectiveness of structural fractures in the second member of the Xujiahe Formation(Xu-2)in the Xinchang-Fenggu area of western Sichuan are not clear.Taking Xu-2 as the research object,field outcrop,drilling core,and logging data were comprehensively utilized,combined with thin section observations,fracture overburden pressure porosity measurements,and the results from permeability experiments.The genetic types and development characteristics of effective structural fractures in Xu-2 were clarified,the main controlling factors of effective structural fracture development were identified,the distribution law of the effective structural fracture plane was revealed,and a geological model of effective structural fracture development was established.The research results show:(1)There are three kinds of natural fractures in Xu-2,including regional structural fractures,structural deformation fractures,and fractures near faults.(2)Regional tectonic fractures are mainly controlled by lithology and lithofacies.The effectiveness of fractures near the fault are mainly affected by the scale of the fault and the degree of stress release,while the effectiveness of structural deformation fractures is mainly controlled by the structural deformation strength and stress deflection.(3)The area can be divided into five geological types:double-fault-clamped fold fractures,single-fault-clamped fold fractures,single-fault-clamped fold fractures,longitudinally bending fold fractures,and structural composites.The double-fault-clamped fold-fracture type formed by north-south-trending and north-east-trending faults has the highest effective fracture development.By considering the"binary type"of early fracture and the factors controlling effective fractures,the development degree of effective fractures in Xu-2 gradually deteriorates from Xinchang to Fenggu.The north-south-trending fault fracture body and composite fold fracture body above the fourth grade of Xinchang-Hexingchang,and the northeast-north-northeast-trending fault fold fracture body and oblique composite fold fracture body of Hexingchang-Fenggu,have the highest development degree of effective fractures,which are the most favorable exploration target areas.These research results provide important reference for studies of the formation mechanism and distribution law of effective fractures in deep and ultra-deep tight sandstone reservoirs in China.