Evaluation of Shale-Gas-Phase Behavior under Nanoconfinement in Multimechanistic Flow

Abstract

Production optimization from shale gas resources is a challenging task, especially when the knowledge of the fluid-phase behavior is not sufficient. Due to nanoscale pores of the shale matrix and higher degree of interactions between the molecules and fluid–pore wall compared to a conventional reservoir, the phase behavior of the shale fluid under confinement is significantly different from that of the bulk fluids observed in a PVT cell. The so-called nanoconfinement effect causes a shift in the critical properties, which could be as high as 60%, and shrinks the phase diagram to a large extent; therefore, correction of thermodynamic properties is vital for accurate reserve estimation and reservoir engineering calculations. In this study, we investigate the effect of confinement on the phase behavior of multicomponent gas in shale media through detailed numerical simulations. The nanoconfinement is accounted for at different levels of pore radii and intrinsic permeabilities in the presence of several major contributing mechanisms to shale gas flow, including but not limited to viscous flow, Knudsen diffusion, gas slippage, pore size variation, and adsorption. The phase envelopes as well as temporal and spatial variations of the composition in the shale matrix block are obtained and analyzed. The theoretical framework and analysis presented herein shed light on the phase behavior of the confined fluid, and the model can be used in shale and tight gas reservoir simulations.

Pore-network modeling of flow in shale nanopores: Network structure, flow principles, and computational algorithms

“…significant confinement, such as capillary pressure and adsorption (Cabral et al, 2005;Chen et al, 2021;Li et al, 2018c;Liu and Zhang, 2019;Mohagheghian et al, 2020). As one apparent phenomenon, the critical point shift is also discussed.…”

“…12. Illustration of phase equilibrium calculations: (a) Typical computational procedures of NPT flash calculations by SSI and Newton's method (Li et al, 2019c), (b) Phase envelopes for effects of capillary pressure (left) (Li et al, 2018c) and critical point shift (right) (Mohagheghian et al, 2020) as a result from the variance of pore radius, (c) Cross-sectional view of the phase equilibrium in pore bodies in a pore network of shale (Chen et al, 2021).…”

Rough Surface Effect on CO2 Displacement at the Nanoscale

“…The N-S equation coupled with multiphase models provides opportunities in overcoming these challenges. 24,25 We employed direct numerical simulation (DNS) to investigate the impact of pore surface roughness on CO 2 displacement of oil in the nanometer pores of shale. The DNS approach here combines the N-S equation with a phasefield model, 26 enabling precise capture of two-phase flow and interfacial behavior, 27 but at a much lower computational cost compared with MD.…”

“…In addition, the MD method, even after coupled with the N-S equation, is still computationally expensive. The N-S equation coupled with multiphase models provides opportunities in overcoming these challenges. , …”

Stability Analysis and Two-Phase Flash Calculation for Confined Fluids in Nanopores Using a Novel Phase Equilibrium Calculation Framework

“…4 Song et al 38 modified Peng− Robinson (PR 39 ) EoS by modifying the molar volume term to describe the shifted critical properties. Mohagheghian et al 40 investigated a shift in critical properties for shale fluid using numerical simulations. The effects of capillary pressure on confined fluids are also non-negligible in nanopores.…”