Laboratory Research on Gas Transport in Shale Nanopores Considering the Stress Effect and Slippage Effect

Abstract

The low permeability of shale, in accretionary complexes and passive continental margins, influences pore pressure generation, and thus induces deformation and fault slip behavior. It is also key in hindering the ability to evaluate shale gas production. Gas is commonly used in measuring the permeability of shale and generally yields high values than that of liquids, due to slippage effect. Separation of the slippage effect from gas permeability is a critical task in the study of low‐permeability media. This study measured the gas permeability (Kg) of the Longmaxi shale parallel to bedding (L1P) and perpendicular to bedding (L1V) under different confining pressures (Cp) and pore pressures (Pp), while simultaneously measuring porosity for different values of Cp. Additionally, a new approach is proposed to define the effective stress coefficient and boundary condition for the Klinkenberg correction. The results show that the Kg of L1P is almost unaffected by the slippage effect, while, for L1V, the Klinkenberg correction is required. The Klinkenberg plot of L1V follows the quadratic model from the study by Ashrafi Moghadam and Chalaturnyk (2014, https://doi.org.10/1016/j.coal.2013.10.008), rather than the classic linear Klinkenberg equation. The results also show that, as the Cp increases and/or the Pp decreases, the contribution of the slippage effect to the L1V Kg increased from 20% to 86.5%. Finally, based on the Knudsen number (Kn), the flow regime of L1P changes from Darcy flow (Kn < 0.01) to slip flow (0.01 < Kn < 0.1), and that of L1V is slip flow.

Measurement of Gas Diffusion Coefficients in Cores of Fine-Grained Lithologies Considering Stress and Adsorption Effects

“…Some studies suggest this is related to the anisotropy of gas channel tortuosity in the core. 28,7 The variation range of methane diffusivity is much more extensive, reaching 3 orders of magnitude. The methane diffusivities of samples YKCO1 and YKCO2 are the smallest, with a range of 4.87−9.17 (×10 −9 , m 2 /s), followed by the methane diffusivity of sample YKCO3, and the methane diffusion coefficient of YKCO4 is the largest, with a range of 2.37−3.97 (×10 −7 , m 2 /s).…”

“…The gas-in-place content and migration ability are critical for developing and evaluating shale gas. − The pores in shale can be classified into two categories: microfractures and matrix pores, and gas follows different migration mechanisms in these two types of pore structures . In microfractures, laminar flow is the primary mechanism, driven by the fluid pressure gradient, and can be described by Darcy’s law and the Hagen–Poiseuille equation or by first-order or second-order slip equations considering the slip effect. − In matrix pores, diffusion mainly dominates fluid transport, as described by Fick’s law. , The effective diffusion coefficient in the matrix is influenced by factors such as matrix pore size, oil–water saturation, and methane adsorption effects. , Among them, the adsorption expansion effect is the focus of research; methane adsorption is generally believed to reduce the pore size, thereby reducing the effective diffusion coefficient. − …”

An Early‐Time Solution of Pulse‐Decay Method for Permeability Measurement of Tight Rocks

“…In pulse‐decay tests, the initial pressure difference between two ends of the sample can be on the order of megapascals (i.e., $${\Delta}P={10}^{6}$$ MPa) (Fedor et al., 2008; Feng & Pandey, 2017). Previous researches show that for the permeability measurements on shale matrix samples, the compressibility of gas density $${\beta }_{\rho }$$ is of the order of 10 7 –10 5 Pa −1 , and those of gas viscosity, sample porosity, intrinsic permeability, and Klinkenberg slippage factor ($${\beta }_{\mu }$$, $${\beta }_{\phi }$$, $${\beta }_{{k}_{int}}$$, $${\beta }_{{b}_{s}}$$) are of the order of 10 −9 to 10 −8 Pa −1 (Chalmers et al., 2012; Dong et al., 2010; Fink et al., 2017; Senger et al., 2018; Sun et al., 2020). Therefore, $${{\Delta}}_{r}{\beta }_{\rho }$$ is of the order of 10 −1 to 10 1 , while the relative changes of the other four parameters ($${{\Delta}}_{r}\mu $$, $${{\Delta}}_{r}\phi $$, $${{\Delta}}_{r}{k}_{int}$$, $${{\Delta}}_{r}{b}_{s}$$) are of the order of 10 −3 to 10 −2 , which are small enough and can be ignored safely.…”

Computational analysis of gas permeability of slip flow through microannulus replete by based‐circular Sierpinski porous medium

“…Flow in porous media was studied theoretically and experimentally in the slip flow regime by several scholars 14‐24 . The analytical solution was feasible with only a simple and specific porous structure.…”

“…In addition, Sun et al 21 performed laboratory research on oil shale to measure permeability, the results point out that the decrease in pore pressure leads to an increase in the slip effect on the permeability.…”