基于电张量矩阵分析裂缝形态对页岩模型等效电特性的影响

Effect of crack geometry on effective electrical properties of shale model using electrical tensor matrix

对具有裂缝结构的各向异性页岩模型等效电特性的研究是非常规油气勘探、页岩储层评价和测井解释的重要基础.针对具有强各向异性的裂缝页岩模型,本文提出使用二阶电学张量矩阵来对裂缝模型的电各向异性进行分析.论文工作采用有限元方法对含针状裂缝和圆盘状裂缝的理想页岩模型进行数值模拟,系统地分析了裂缝的形状、体积以及在岩体中的不同位置形态对页岩等效电参数张量的影响.结果表明:裂缝的存在是导致岩石模型表现出电各向异性的原因之一;当裂缝的体积相同时,裂缝的形状以及裂缝的位置不同,都会使页岩模型的介电张量出现较大差异,并随裂缝相对位置及角度改变而呈现一定规律.这一研究结果有望为电磁测井和页岩油页岩气参数的反演提供关键的理论参考依据.

The investigation of the effective electrical properties for the anisotropic shale model with cracks is an important foundation of unconventional oil and gas exploration, shale reservoir evaluation and logging interpretation. For cracked shale models with strong anisotropy, a two-order electrical tensor matrix is proposed in this paper to analyze the electrical anisotropy of cracked shale models. In this paper, the idealized shale physical models containing needle-like cracks and disk-like cracks are numerically simulated by the Finite Element Method(FEM), and the effect of geometrical parameters, such as crack shape, crack volume and the different positions of crack in the shale, on the effective electrical parameter tensor of shale are systematically analyzed. The research results show that the existence of the crack is one of the reasons for the anisotropy of the electrical properties of shale;when the volume of crack is the fixed, the dielectric tensor of the shale models are greatly different while the shape of cracks and the position of cracks are different. In the meantime, the dielectric tensors of the shale model show a certain pattern and variation trend along with the variation of the relative position and angle of the crack. The research conducted for the effective electrical properties of anisotropic shale model will provide valuable theoretical reference for the application of electromagnetic logging as well as the physical characteristic inversion for shale oil and gas.