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Energies 2018, 11(1), 223; https://doi.org/10.3390/en11010223

Gas Transport Model in Organic Shale Nanopores Considering Langmuir Slip Conditions and Diffusion: Pore Confinement, Real Gas, and Geomechanical Effects

1
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China
2
Research Center of China United Coalbed Methane Corporation, Ltd., Beijing 100011, China
3
Xinjiang Oilfield Company Capital Construction Engineering, Karamay, Xinjiang 834000, China
*
Authors to whom correspondence should be addressed.
Received: 3 December 2017 / Revised: 27 December 2017 / Accepted: 12 January 2018 / Published: 17 January 2018
(This article belongs to the Special Issue Flow and Transport Properties of Unconventional Reservoirs)
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Abstract

Nanopores are extremely developed and randomly distributed in shale gas reservoirs. Due to the rarefied conditions in shale strata, multiple gas transport mechanisms coexist and need further understanding. The commonly used slip models are mostly based on Maxwell slip boundary condition, which assumes elastic collisions between gas molecules and solid surfaces. However, gas molecules do not rebound from solid surfaces elastically, but rather are adsorbed on them and then re-emitted after some time lag. A Langmuir slip permeability model was established by introducing Langmuir slip BC. Knudsen diffusion of bulk phase gas and surface diffusion of adsorbed gas were also coupled into our nanopore transport model. Considering the effects of real gas, stress dependence, thermodynamic phase changes due to pore confinement, surface roughness, gas molecular volume, and pore enlargement due to gas desorption during depressurization, a unified gas transport model in organic shale nanopores was established, which was then upscaled by coupling effective porosity and tortuosity to describe practical SGR properties. The bulk phase transport model, single capillary model, and upscaled porous media model were validated by data from experimental data, lattice Boltzmann method or model comparisons. Based on the new gas transport model, the equivalent permeability of different flow mechanisms as well as the flux proportion of each mechanism to total flow rate was investigated in different pore radius and pressure conditions. The study in this paper revealed special gas transport characteristics in shale nonopores and provided a robust foundation for accurate simulation of shale gas production. View Full-Text
Keywords: apparent permeability model; Knudsen diffusion; Langmuir slip condition; shale gas reservoir; surface diffusion apparent permeability model; Knudsen diffusion; Langmuir slip condition; shale gas reservoir; surface diffusion
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Zhang, L.; Shan, B.; Zhao, Y.; Du, J.; Chen, J.; Tao, X. Gas Transport Model in Organic Shale Nanopores Considering Langmuir Slip Conditions and Diffusion: Pore Confinement, Real Gas, and Geomechanical Effects. Energies 2018, 11, 223.

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