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Appl. Sci. 2018, 8(7), 1063; https://doi.org/10.3390/app8071063

A Fully Coupled Model for the Simulation of Gas Flow in Multiscale Shale Reservoirs Combining Multiple Effects

1,2,* , 1,2,* , 1,2
and
1,2
1
Coalbed Methane Resources and Reservoir Formation Process Key Laboratory of Ministry of Education, China University of Mining & Technology, Xuzhou 221008, Jiangsu, China
2
School of Resources and Geoscience, China University of Mining & Technology, Xuzhou 221116, Jiangsu, China
*
Authors to whom correspondence should be addressed.
Received: 29 May 2018 / Revised: 19 June 2018 / Accepted: 26 June 2018 / Published: 29 June 2018
(This article belongs to the Special Issue Nanotech for Oil and Gas)
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Abstract

Gas flow mechanisms in shale reservoirs with multiscale pores and fractures are extremely complex. In this study, a dual fracture framework model was adopted to describe gas flow in multiscale shale reservoirs. Gas flow through a shale reservoir occurs through both the shale matrix and hydraulic fractures. This study considered bulk phase and adsorbed gas flow in the shale matrix. Next, a series of partial theories were combined to derive a fully coupled model simulating gas flow in multiscale shale reservoirs: (1) fractal theory was adopted to obtain the pore distribution within shale reservoirs; (2) mechanical equilibrium equations were used to investigate the stress-sensitivity of permeability and porosity; and (3) a Langmuir adsorption model was applied to describe the effects of gas adsorption/desorption. The proposed model was validated using traditional models as well as field data on gas production from Marcellus Shale, and was subsequently applied to study variations of mass flux in various flow regimes with respect to reservoir pressure. We found that mass flux in the slip flow regime decreased at first and then increased with decreasing reservoir pressure, while in the continuum regime, Knudsen diffusion and surface diffusion the mass flux decreased with decreasing reservoir pressure. Stress-sensitivity has a significant impact on bulk phase gas flow, while adsorption/desorption influence both the bulk phase gas flow and adsorbed gas flow. At high pressures, the impact of stress-sensitivity on total gas mass flux is greater than that of adsorption/desorption, while the reverse was true for low pressures. The proposed model shows promising applications for analyzing various gas flow regimes in multiscale pores/fractures, and accurately evaluating in situ apparent permeability. View Full-Text
Keywords: shale reservoirs; hydraulic fractures; matrix; flow regime; stress-sensitivity; adsorption/desorption shale reservoirs; hydraulic fractures; matrix; flow regime; stress-sensitivity; adsorption/desorption
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Hou, X.; Zhu, Y.; Liu, Y.; Wang, Y. A Fully Coupled Model for the Simulation of Gas Flow in Multiscale Shale Reservoirs Combining Multiple Effects. Appl. Sci. 2018, 8, 1063.

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