川东北通江地区须家河组天然裂缝发育规律及控制因素

Development laws and controlling factors of natural fractures of Xujiahe Formation in Tongjiang area,northeastern Sichuan

致密砂岩储层天然裂缝的发育规律对气藏富集和单井产能有重要影响。文中基于地表露头、岩心、薄片、地球物理和试气试采等数据资料,明确了通江地区上三叠统须家河组天然裂缝的发育规律和控制因素,建立了裂缝发育地质模式,提出了气藏甜点类型和分布范围。研究表明:1)通江地区须家河组致密砂岩储层发育构造成因和非构造成因的2种天然裂缝;2)天然裂缝的优势方位为近南北向,以中高角度裂缝为主;3)天然裂缝的发育程度受岩性、岩石力学层厚和构造作用等因素联合控制,粉砂岩是裂缝发育的优势岩性,断层面和褶皱核部是裂缝发育的有利部位;4)结合地震预测结果,明确了距断层面小于300 m且距褶皱枢纽面小于400 m的裂缝发育带为须家河组致密储层的裂缝甜点区。研究结果可为该区的储量评价和井位部署提供依据。

The development laws of natural fractures in tight sandstone reservoirs have a significant impact on gas reservoir enrichment and single well productivity.Based on outcrops,cores,thin sections,geophysics and gas testing data,the laws and controlling factors of natural fractures in Xujiahe Formation of Upper Triassic in Tongjiang area were clarified,a geological model for fracture development was established,and the types and distribution range of sweet spots in gas reservoirs were proposed.The research shows that:(1)There are two types of natural fractures developed in the tight sandstone reservoir of Xujiahe Formation in Tongjiang area,namely tectonic fractures and non-tectonic fractures.(2)The optimal orientation of natural fractures is near southnorth,and natural fractures are mainly middle-high angle fractures.(3)The degree of development of natural fractures is jointcontrolled by factors such as lithology,rock mechanical layer thickness and tectonism.Siltstone is the dominant lithology for fracture development,and fault surfaces and fold cores are favorable parts for fracture development.(4)Combined with seismic prediction results,it is clarified that the fracture development belt less than 300 m away from the fault surface and less than 400 m away from the fold hinge surface is the fracture sweet spot area of the tight reservoir of Xujiahe Formation.The research result can provide a basis for reserve evaluation and well loction deployment in this area.