四川LZ页岩储层现今地应力方向及主控因素——以龙一段为例

Present Stress Orientations and Controlling Factors of Shale Reservoirs in LZ Region,Sichuan Basin:Example of the First Member of Longmaxi Formation

现今地应力场方向是影响页岩储层压裂改造效果的主要因素之一,进行现今应力场方向展布特征及其主要影响因素分析对页岩气开发应用具有重要的意义。利用古地磁结合波速各向异性法、微地震监测法、测井资料3种方法来判别地应力方向,对LZ地区地应力方向平面展布特征及主控因素分析。结果表明:宽缓向斜处3种解释方法都适用,准确度和可信度排序为岩心实验测试、偶极横波测井、电成像测井。断裂影响区域偶极横波测井不再适用,岩心实验测试结果可信度大于电成像测井。裂缝发育强构造变形区域对3种方法解释结果均有影响,需多种方法结合分析;LZ地区龙马溪组现今最大主应力方向变化范围在90°~125°。得胜、宝藏、云锦向斜的最大主应力方向在约115°,福集向斜最大水平主应力方向偏转最大,在80°~100°,可能与西侧华蓥山断裂逆冲兼具走滑有一定关系。断裂规模越大其扰动范围和强度越大。Ⅰ、Ⅱ、Ⅲ、Ⅳ级断裂最大扰动范围分别为1100、850、500、300 m。紧闭背斜褶皱变形区,受褶皱顶部派生的拉张应力影响,地应力方向沿着褶皱轴向偏转,靠近褶皱顶部,受拉张应力影响大,偏转角度最大。研究成果可为后期水平井井位轨迹优化及压裂改造工程提供理论支撑。

The direction of the current geostress field is one of the main factors affect the effect of shale reservoir fracturing transformation,it is of great significance to carry out the study of the azimuth distribution characteristics of the current stress field and its main controlling factors for the development and application of shale gas.The paleomagnetism combined with wave velocity anisotropy method,microseismic monitoring method and logs data were used to determine the direction of ground stress,and the distribution characteristics and main control factors of the ground stress plane in the research area were analyzed on the basis of this.The results show that the three interpretation methods of wide and slow oblique are applicable,and the accuracy and credibility are ranked as core experimental test,dipole transverse wave logging,and electrical imaging logging.Dipole transverse wave logging in the fracture-affected region is no longer applicable,and the confidence of core experimental test results is greater than that of electrical imaging logging.The deformation area of strong fracture development has an influence on the interpretation results of the three methods,and multiple methods are required to be combined and analyzed.The current maximum principal stress direction of the Longmaxi Formation region ranges from 90°to 125°in LZ.The maximum principal stress direction of victory,treasure and Yunjin oblique is about 115°,and the maximum horizontal main stress direction of Fuji oblique is the largest,between 80°and 100°,which may be related to the reverse thrust of the Huaying Mountain fault on the west side and slippage.The larger the fracture scale,the greater the range and intensity of the disturbance.The maximum disturbance range of I,II,III and IV fracture is 1100,850,500,300 m,respectively.Tightly closed the dorsal fold deformation area,affected by the tensile stress derived from the top of the fold,the ground stress direction is deflected along the axial direction of the fold,close to the top of the fold,greatly affected by tensile tension stress,and the deflection angle is the largest.The research results can provide theoretical support for the trajectory optimization of the horizontal well in the later stage and the fracturing transformation project.