Effect of Bedding Planes on the Permeability and Diffusivity Anisotropies of Berea Sandstone

Abstract

Evaluating the anisotropy of transport parameters in rocks is important for various applications, such as reservoir engineering and rock mechanics. Owing to their anisotropic pore structures, the tortuosity, constrictivity, and pore size distribution of rocks are often anisotropic in nature, which in turn affect the permeability and diffusivity. However, it has still not been determined whether the permeability and diffusivity are anisotropic in the same manner. This study used experiments and numerical modeling to examine the effect of the pore structure on the permeability and diffusivity anisotropies of rocks. The experimental results showed a clear difference in the anisotropy ratios of the permeability (k ⊥ /k) and diffusivity (D ⊥ e /D e) for Berea sandstone, which is the de facto standard porous sandstone. The analysis results from micro-focus X-ray computed tomography and simulation with the lattice Boltzmann method supported the experimental difference in anisotropy ratios. In the analysis and simulation, the relation between the minimum cross-sectional porosity area and characteristic pressure gradient was estimated. The analysis results suggest that the minimum cross-sectional porosity areas that influence the permeability anisotropy are too large to physically induce anisotropic NaCl diffusion, and thus, the diffusivity of Berea sandstone is nearly isotropic.

Benchmark study using a multi-scale, multi-methodological approach for the petrophysical characterization of reservoir sandstones

“…In this respect, permeability anisotropy in sandstones at a small scale is usually attributed to the shape or preferential orientation of grains and pores (e.g. Sato et al, 2019) and to a heterogeneous distribution of cementing material at grain contacts (Louis et al, 2005). Clay-free and cementfree layers in S1 thus constitute the main avenues for flow in the parallel direction, shown by variation in porosity in the z direction (Fig.…”

“…Tiab and Donaldson, 2004). For comparison, the values of this ratio obtained from experimental permeability measurements were ∼ 1.2 for Bentheim sandstone (Louis et al, 2005), ∼ 1.7-2.5 for a sandstone within the Cretaceous Virgelle Member, Alberta, Canada (Meyer and Krause, 2001), and ∼ 8.5 for Berea sandstone (Sato et al, 2019). However, in our laboratory measurements conducted parallel to the layering (in the x-y plane), poorly cemented grains in S3 could dislocate from the weakly consolidated sample due to the application of a pressure gradient.…”

“…Meyer, 2002;Farrel et al, 2014). Preferential fluid flow pathways are inherently connected to rock microstructure, formed by depositional sedimentary structures such as pore shapes and their preferential orientation (Sato et al, 2019) or lamination (Lewis, 1988). Those can be modified with time by dissolution of grains, by grain rearrangement and pore collapse (Halisch et al, 2009;Clavaud et al, 2008), by cementation (Louis et al, 2005) or by deformation structures (fractures).…”

Benchmark study using a multi-scale, multi-methodological approach for the petrophysical characterization of reservoir sandstones

“…In this respect, permeability anisotropy in sandstones at a small scale is usually attributed to the shape or preferential orientation of grains and pores (e.g., Sato et al, 2019) and to a heterogeneous distribution of cementing material at grain contacts (Louis et al, 2005). At a larger scale, a higher degree of permeability anisotropy is associated with the presence of localized beds, foliation, and compaction bands that constitute barriers to flow in the perpendicular direction (see Halisch et al, 2009;Clavaud et al, 2018 and references therein).…”

“…Gas permeability measurements indicate anisotropy, yielding permeabilities of 4600 mD in the x-y plane and 220 mD in the z-direction (with an anisotropy ratio of ~20, defined here as κ||/ κ⊥, e.g., Tiab and Donaldson, 2004). For comparison, the values of this ratio obtained from experimental permeability measurements were ~1.2 for Bentheim sandstone (Louis et al, 2005), ~1.7-2.5 for a sandstone within the Cretaceous Virgelle Member, Alberta, Canada (Meyer and Krause, 2001), and ~8.5 for Berea sandstone (Sato et al, 2019). However, in some laboratory measurements conducted parallel to the layering (in the x-y plane), poorly cemented grains in S3 were dislocated from the weakly consolidated sample due to the application of a pressure gradient.…”