正交各向异性岩石弹性参数的空间展布

The Spatial Distribution of Elastic Parameters of Orthotropic Rocks

桂俊川 陈平 马天寿

GUI Junchuan CHEN Ping MA Tianshou

油气藏地质及开发工程国家重点实验室·西南石油大学, 四川 成都 610500

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China

岩石力学参数是研究井壁稳定和压裂改造的基础参数，其值可以根据刚度矩阵来计算。目前基于刚度矩阵计算岩石力学参数的模型均将地层视为VTI介质，欠缺对实际地层中大量存在的ORT特征的考虑，并忽视了观测坐标系对岩石力学性质的影响。本研究考虑页岩气地层ORT特性，基于岩石本构方程，推导出岩石力学参数的刚度参数表达式。首先，从岩石本构关系出发，推导出岩石力学参数的刚度矩阵表达式；其次，考虑井眼与地层的交角，结合岩石力学参数的定义，通过坐标变换，建立了观测坐标系下岩石力学参数的计算方法，并对不同观测坐标系下的岩力学参数进行了分析比较；最后，考虑实际地层由页岩-砂岩互层组成，研究了砂岩含量的变化对观测坐标系下岩石力学参数的影响。

The mechanical parameters of rocks are the basic parameters for studying the wellbore stability and fracturing reformation. Their values can be calculated based on the stiffness matrix. Currently, the models used for calculating the mechanical parameter of rocks based on the stiffness matrix consider the formation as a VTI medium. This approach failed to take into consideration of the significant amount of ORT features in the actual formation and the effect of observation coordinate systems on the mechanical properties of rock. In this study, the expression of the stiffness parameter used for calculating the rock mechanical parameters was derived based on the constitutive equation of rock and considering the ORT features of shale gas formations. First, the expression of the stiffness matrix used for calculating the rock mechanical parameters was derived from the constitutive relation of the rock. Next, by considering the intersection angle between the wellbore and the stratum, combining the definition of mechanical parameters for rock, and performing coordinate transformation, a method for calculating the mechanical parameters of rocks was established in the observation coordinate system. The mechanical parameters of rocks in different observation coordinate systems were also analyzed and compared. Finally, considering that the actual formation is composed of shale-sandstone interbeds, we analyzed the influence of the variation in sandstone content on the mechanical parameters of rock in the observation coordinate system.

10.11885/j.issn.1674-5086.2018.09.21.02