四川盆地龙马溪组页岩气储层各向异性岩石物理建模及应用（英文）

Anisotropy rock physics model for the Longmaxi shale gas reservoir,Sichuan Basin,China

不同类型的页岩,微观物性特征差异明显,本文针对四川盆地龙马溪组页岩气储层进行岩石物理建模及VTI各向异性参数反演。首先,基于前人对粘土矿物的定向排列是产生页岩固有各向异性主要原因这一地质认识,在岩石物理建模过程中引入粘土矿物压实指数CL参数描述粘土矿物的弹性各向异性。之后,基于岩石物理模型开发反演算法,计算页岩储层CL参数及Thomsen各向异性参数,解决了由于无法测得与井壁垂直方向上的声波速度,各向异性直接测量存在困难的问题。计算结果表明,通过在岩石物理建模中引入粘土压实参数,反演方法能够合理估计龙马溪页岩储层的弹性各向异性,反映了龙马溪页岩的微观物性特征。进一步分析发现,龙马溪页岩中粘土含量与参数CL相关性较弱,表明粘土矿物的多少对其压实或各向异性程度影响较小。同时,参数CL在目标层龙马溪组底部和五峰组具有高异常值,反映了储层微观结构与含油气特征具有关联性。最后,基于模型构建了岩石物理模板,可用于储层测井数据与多物性参数关系的定量解释。测井数据在岩石物理模板上的合理分布也验证了岩石物理建模方法的有效性。

The preferred orientation of clay minerals dominates the intrinsic anisotropy of shale. We introduce the clay lamination （CL） parameter to the Backus averaging method to describe the intrinsic shale anisotropy induced by the alignment of clay minerals. Then, we perform the inversion of CL and the Thomsen anisotropy parameters. The direct measurement of anisotropy is difficult because of the inability to measure the acoustic velocity in the vertical direction in boreholes and instrument limitations. By introducing the parameter CL, the inversion method provides reasonable estimates of the elastic anisotropy in the Longmaxi shale. The clay content is weakly correlated with the CL parameter. Moreover, the parameter CL is abnormally high at the bottom of the Longmaxi and Wufeng Formations, which are the target reservoirs. Finally, we construct rock physics templates to interpret well logging and reservoir properties.