川中地区中下侏罗统致密油储层裂缝发育特征

摘要

裂缝是川中地区中下侏罗统致密油储层重要的储集空间和主要的渗流通道，影响油气富集和单井产能。利用野外露头、岩芯和成像测井资料，对川中地区致密储层裂缝成因类型和发育特征进行了系统分析。在地质成因上，该区中下侏罗统沙溪庙组一段致密砂岩和大安寨组致密灰岩储层的裂缝可以分为构造裂缝与成岩裂缝两种类型，其中以构造裂缝为主。按照裂缝倾角，构造裂缝可以进一步分为低角度裂缝(0°~30°)、斜交裂缝(30°~60°)和高角度裂缝(大于60°)。由于低角度裂缝的直井钻遇率高，而斜交裂缝与高角度裂缝的直井钻遇率依次降低，所以对其裂缝密度统计时需要进行校正。根据裂缝与岩芯的空间几何关系，采用裂缝面法线方向上单位长度的裂缝条数进行校正。结果表明，该区沙溪庙组一段和大安寨组高角度裂缝线密度远大于低角度裂缝，反映该区致密油储层具有以高角度裂缝为主的特点，修正了过去长期以低角度裂缝为主的认识，对深入认识该区裂缝发育规律和指导致密油勘探开发具有重要意义。%Fractures are important storage space and fluid channels, influencing oil-gas accumulation and well production in the Middle-Lower Jurassic tight oil reservoirs in central Sichuan Basin.Based on the data of analogous outcrops,cores and image logs,the fracture origin types and development characteristics were systematically analyzed.According to the geological origins,the tectonic and diagenetic fractures are developed in the Middle-Lower Jurassic tight oil reservoirs of the first member of Shaximiao Formation and Da’anzhai Formation in central Sichuan Basin,and the tectonic fracture is the main one.According to the dip angles of fractures,the fractures can be divided into three types,i.e.low dip-angle fractures (0°-30°),oblique dip-angle fractures (30°-60°)and high dip-angle fractures (more than 60°).Because low dip-angle fractures present high encountered rates in vertical wells,and oblique and high dip-angle fractures present gradual decrement of encountered rates,it is necessary to make a correction related to fracture intensity statistics.According to the spatial geometric relationship of fracture and core,the fracture number per meter of length in the normal direction of fracture surface was used to correct the calculation.The results show that the linear intensities of high dip-angle fractures are much greater than those of low dip-angle fractures in the first member of Shaximiao Formation and Da’anzhai Formation;high dip-angle fractures are the most abundant in these tight oil reservoirs;thus,it corrects the past understanding that low dip-angle fractures are the major,which is of great significance for further understanding fracture development rules and guiding tight oil exploration and development in this area.