储集层多尺度裂缝特征及控制因素——以准噶尔盆地南缘侏罗系—白垩系为例

Characteristics and controlling factors of multi-scale fractures in reservoir:A Jurassic-Cretaceous case from the southern margin of Junggar Basin

准噶尔盆地南缘侏罗系—白垩系储集层中裂缝较发育,本文基于地表露头、岩心、薄片和测井等资料,运用工业CT、激光共聚焦、扫描电镜等技术手段,系统研究了储集层多尺度裂缝类型、分布特征及成因,并对裂缝形成的控制因素进行了分析,认为南缘侏罗系—白垩系储集层裂缝可分为三级,分别是Ⅰ级宏观裂缝、Ⅱ级微细裂缝、Ⅲ级显微裂缝,再根据裂缝长度和成因将Ⅰ级宏观裂缝分为Ⅰ,Ⅰ两类,Ⅲ级显微裂缝分为Ⅲ,Ⅲ两类.研究结果表明:由天山造山带到盆地内部Ⅰ级宏观裂缝发育程度由强到弱,裂缝密度由第1排的1.6条/m到第3排的0.8条/m;Ⅱ级微细裂缝主要发育在各构造带的砂岩储集层中;Ⅲ级显微裂缝主要发育在第1排构造带的砂砾岩储集层中和北部斜坡带的砂岩储集层中.南缘侏罗系—白垩系储集层裂缝发育程度受构造应力、储集层岩性及岩矿组成、储集层厚度等因素控制.构造应力强则裂缝发育程度高,单层厚度较薄的细砂岩、中砂岩较粉砂岩、粗砂岩和砂砾岩更易发育裂缝.长英质碎屑颗粒、碳酸盐胶结物含量高的储集层更易发育裂缝.

Fractures are widely developed in the Jurassic-Cretaceous reservoirs in the southern margin of the Junggar Basin. Based on the observation of the outcrop sections, cores and thin sections, combined with the use of logging data, computed tomography(CT), confocal microscope and scanning electron microscope(SEM), the study analyzed the classification, distribution and origin of the fractures in the reservoir at different scales. The fractures in research areas can be divided into three levels, which are level-1 macro fracture, level-2 mini fracture and level-3 micro fracture. Based on the length and origin of fractures, macro fracture and micro fracture respectively can be further divided into two sub-levels. The results indicate that the development degree of macro fractures decreases from the Tianshan orogen to the inner basin. The density of macro fractures reduces from 1.6 fractures per meter in the first row of the structural belt to 0.8 fracture per meter in the third row of the structural belt. Mini fractures are mostly developed in the sandstone reservoir in the structural belt area, whereas micro fractures are mostly developed in the conglomerate reservoir in the first row of structural belt and in the sandstone reservoir in the northern basin-slope area. The development of fractures in Jurassic-Cretaceous reservoir is controlled by the tectonic stress, lithology and the thickness of the reservoirs. Fractures are more easily to develop where the tectonic stress is stronger. Fractures are better developed in medium-fine sandstone than siltstone, coarse sandstone and conglomerate, especially in the reservoir whose bedding thickness is thinner. Fractures are more easily developed in the reservoir which has more felsic minerals and carbonate cement.