四川盆地大邑地区须家河组裂缝成因探讨

摘要

According to field survey,drilling cores,thin slice and logging data,based on the tectonic stress field analysis,this paper analyzed the types and origin of fractures of the Xujiahe Formation in the Sichuan Basin.The result shows that under the action of the NW horizontal compressive stress in the late stage of Indo-China movement,the approximate NS and NW trending＂X＂ plane conjugate shear fractures and a few NE trending tectonic associated fractures were formed.Due to the influences of the strong stratum heterogeneity,the development degree of NW trending fractures is higher.During the period of late-mid-Himalayan movement,under the action of the EW horizontal compressive stress,the former fractures were reformed that the NW-SE trending fractures were enhanced and the NS trending fractures developed into thrust fault with strike-slip characteristics.And in the NE local stress field,approximate EW trending fractures developed in the northeastern study area.Under the action of nowadays NW trending tectonic stress field,the NW trending fractures are more open,and the approximate NS and NE trending fractures are closed.The distribution of regional fractures superposed associated fractures is closely related to local structures.The area where kinds of fractures developed is favorable for fracture development,so the development area of NW and approximate EW trending effective fractures will be the key area for oil-gas exploration in Dayi area.%根据野外调查、岩心、薄片和测井等资料,在构造应力场分析的基础上,对四川盆地大邑地区须家河组裂缝类型及其成因进行了分析。结果表明：印支运动晚期,在北西向水平挤压应力作用下形成了近南北向和北西向的平面＂X＂型剪切缝及少量的北东向构造伴生缝,由于岩层非均质性,北西向裂缝发育程度较高;喜山运动中晚期,东西向水平挤压应力对早期裂缝进行改造,北西向高角度剪切缝继续发育,而少量近南北向高角度裂缝发育为具左旋走滑性质的近南北向逆断层,同时,在北东向局部应力场的作用下,研究区北东部发育近东西向裂缝。在现今北西向构造应力场作用下,北西向裂缝张开度增大,为有效缝,而近南北向、北东向裂缝闭合。区域构造缝叠加局部构造伴生缝的分布与局部构造密切相关,多类裂缝交织发育的地区为裂缝发育区。北西向和近东西向有效裂缝发育区域可作为大邑地区油气勘探的重点区域。