吐哈盆地北部凹陷低渗透砂岩储层裂缝发育特征及成因

吐哈盆地北部凹陷低渗透砂岩储层发育有4组高角度裂缝和一组近水平裂缝.高角度裂缝主要为构造成因的剪切裂缝,低角度裂缝包括成岩裂缝、顺层滑脱裂缝和近水平剪切裂缝3类.裂缝的发育程度受岩性、岩层厚度、构造部位等因素的控制.裂缝是低渗透储层的主要渗流通道,是控制其油气产能高低的主要因素.通过地质和数值模拟研究,该区NE和NW向高角度裂缝为在燕山早期近SN向水平挤压作用下形成的共轭剪切裂缝,近EW向高角度裂缝和近水平剪切裂缝为燕山晚期近SN向逆冲推覆作用下形成的共轭剪切裂缝,近SN向裂缝主要与晚期的近SN向不均匀挤压作用有关.

Development characteristics and geneses of the fractures in low-permeability sandstone reservoir in the nothern depression of Tuha Basin

According to the analyses of cores,thin sections and surface outcrops,there are four sets of high dip-angle fractures and one set of approximately horizontal fracture in the low-permeability sandstone reservoir in the northern depression of Tuha Basin.The fractures with high dip-angle are mainly the shear fractures formed by tectonic stress field.The fractures with low dip-angles include diagenetic fracture,along-bedding detachment fracture and approximately horizontal shear fracture.The development degree of the fractures is controlled by the factors of lithology,strata thickness and structural position,etc.The fractures are the main seepage channels of the low-permeability reservoir and the main factor of influencing oil and gas output.According to geological analysis and numerical simulation,it is held that the NE and NW fractures with high dip-angle are the conjugate shear fractures formed by the horizontal compression in approximately SN direction in early Yanshan,the EW fracture with high dip-angle the and approximately horizontal shear fracture are the conjugate shear fractures formed by the thrust-nappe in approximately SN direction in late Yanshan,and the formation of approximate SN fractures are related to the inhomogeneous compression in approximately SN direction in late stage.