Material Constants of Anisotropic Poroelasticity and Its Impacts on Shale Gas Production

Abstract

While the production of shale gas is always accompanied by stratum deformation, previous studies have commonly assumed isotropy to simplify the modeling process despite substantial experimental evidence supporting the anisotropy of these formations. This work contributes to both theoretical and practical aspects of anisotropy. For the theoretical aspect, a novel mixture theory approach is used to explore the poromechanical constants of anisotropic poroelasticity. By incorporating new elements in the modeling of intrinsic solid density and unjacketed frame deformation, we are able to establish a complete set of parameters considering micro-inhomogeneity and micro-anisotropy in a macroscopically anisotropic porous medium like shale. The bounds on the material constants are established, and their relationship with the intrinsic material constants of poroelasticity proposed by Cheng ( 2021) is discussed. In a practical context, we examine the impacts of anisotropy in a 3D shale gas reservoir considering both elastic and permeability anisotropy. For elastic anisotropy, compared with the isotropic counterpart, we identify significant dissimilarities in the horizontal stress parallel to the wellbore (σ xx here) between assumptions of isotropy and transverse isotropy. For permeability anisotropy with an inclined plane of isotropy, the gas production is largely inhibited, and we could observe the stress distribution reorientation. To conclude, isotropic models are unable to reproduce the stress changes predicted by the anisotropic models, and this research contributes to a better understanding of anisotropy in shale gas reservoirs.

Anisotropic continuum framework of coupled gas flow – adsorption – deformation in sedimentary rocks

“…The well radius is 0.1 m. We choose this geometry size to better capture the dynamics near the well since a fine mesh is required near the well, similar to those in Cao et al 72 and Zhang et al 86 We think for the field scale, our findings are still applicable. 87 Tractions are applied at the outer boundary as 𝜎 𝑥𝑥 = −35 MPa and 𝜎 𝑦𝑦 = −40 MPa. The finite element mesh information of the problem is given in…”

“…𝐾 ′ 𝑠 ≠ 𝐾 ′′ 𝑠 implies the micro-heterogeneity of the material, which is not the focus of this work. Interested readers may refer to Cheng 51 and Zhang et al 87 for more details.…”

Numerical Analysis of the Stress Shadow Effects in Multistage Hydrofracturing Considering Natural Fracture and Leak-Off Effect

“…This stress shadow effect increases the subsequent perforation fracturing pressure, altering the original geo-stress state and the fracture expansion direction. The fracture formation process exhibits the "3S" effect of stress accumulation, stress transfer, and stress shadow [5,6]. In the 1980s, Warpinski and Teufel began studying the interaction between fractures, providing an analytical solution for the stress field of a hydraulic fracture with constant height and finite length [7].…”