川东南DS地区龙马溪组页岩裂缝发育特征及主控因素

Development characteristics and controlling factors of shale fractures in the Longmaxi Formation in DS area,southeast Sichuan

川东南DS地区下志留统龙马溪组页岩裂缝发育,通过野外地质调查和典型取心井岩心观察,结合包裹体均一温度和X衍射等实验测试结果,对裂缝发育特征及主控因素进行研究。结果表明:研究区主要发育2期裂缝,Ⅰ期发生在燕山运动中晚期,主要受江南雪峰隆起NW向挤压,形成近EW向和SSE向平面X型共轭剪切缝和NE向剖面剪切缝;Ⅱ期发生在燕山运动末期—喜马拉雅期,主要受NE向挤压,形成NNE向和NEE向平面X型共轭剪切缝和NW向剖面剪切缝,该期为受川中古隆起、江南雪峰隆起和黔中隆起叠合作用影响。裂缝发育特征主要受构造作用和构造部位、岩石力学性质、岩性和矿物成分等因素影响,其发育程度与距断层的距离、岩石脆性矿物和粘土矿物含量、杨氏模量、泊松比等关系密切。

Fractures developed well in the Lower Silurian Longmaxi Formation in DS area,southeast Sichuan. The development characteristics and controlling factors of shale fractures were studied based on the experimental results of field geological survey,core observation of typical well,homogeneous temperature of inclusions and X-ray diffraction. The results show that there are 2 periods of fracture development in the area. The first period is at the middle-late Yanshan movement,which was dominated by NW compression induced by the rise of Jiangnan Xuefeng uplift,and near EW and SSE X-type conjugate shear fracture in plane and NE longitudinal shear fracture developed. The second period is from the end of Yanshan movement to the Himalayan period,which was dominated by NE compression as a combined effect of the rise of central Sichuan paleo-uplift,Jiangnan Xuefeng uplift and central Guizhou uplift. As a result,NNE and NEE X-type conjugateshear fracture in plane and NW longitudinal shear fracture developed. The development of fractures is mainly controlled by tectonic movement,structural position,rock mechanical properties,lithology and mineral composition. The degree of fracture development is closely related to the distance from the fault,the content of brittle mineral and clay mineral of rock,Young's modulus and Poisson's ratio.