Abstract

A simple method to deal with cracklike pores in anisotropic matrix rock such as shales enhances analytical models and their applications. Actually, clayrocks (shales, in particular) are the dominant clastic component in sedimentary basins, representing about two-thirds of all sedimentary rocks. Shales are usually assumed to be transversely isotropic (TI) media. They are known to be highly anisotropic because of (1) intrinsic elastic anisotropy of the solid phase (matrix) forming the rock (more or less ordered clay layers) and (2) anisotropy induced by the presence of cracklike pores. We focus on this second component of anisotropy. Current analytical models deal with it, but they are complex and are restricted in the case of matrix TI symmetry to cracks lying in the symmetry plane. We simplify such models within a reasonably good approximation and develop an analysis scheme in which cracklike pore effects are calculated in an equivalent isotropic matrix. This simplifies the theoretical approach and potentially broadens its application to any crack and/or pore orientation, e.g., damaged shale with horizontal and vertical (perpendicular to the bedding plane) cracks. A high-pressure confinement test provides experimental data for checking the proposed tool against a reference model in the case of cracklike pores lying in the bedding plane. The results (in terms of Thomsen parameters) are consistent with results from large-scale field data.

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