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Experimental and Numerical Study on Gas-Displacing-Water in Coal Reservoirs under Different Confining Pressures Using
Kaide Liu1, Qiyu Wang1, Yu Xia1
1Xijing University, Shaanxi Key Laboratory of Safety and Durability of Concrete Structures, Xi'an 710123, P.R. China.
ACS Omega
|July 24, 2026
Summary
Deep coalbed methane extraction is vital for energy, but faces challenges from stress and temperature. This study reveals how confining pressure affects gas-water flow, optimizing extraction strategies for enhanced CBM production.
Area of Science:
- Earth Sciences
- Energy Engineering
- Geomechanics
Background:
- Depletion of shallow coal resources necessitates deep coalbed methane (CBM) extraction.
- Deep CBM reservoirs are constrained by low permeability, heterogeneity, and coupled in situ stress and geothermal conditions.
- Existing studies lack consideration of dynamic stress paths and temperature field synergy, limiting practical application.
Purpose of the Study:
- To systematically investigate confining pressure-dominated gas-displacing-water behavior in deep coal reservoirs.
- To integrate low-field nuclear magnetic resonance (LF-NMR) and thermo-hydro-mechanical (THM) coupled numerical simulation.
- To provide a quantitative basis for optimizing deep CBM extraction technologies.
Main Methods:
- Laboratory experiments at a constant temperature (25 °C) using control variable method to isolate confining pressure effects.
- Real-time monitoring using low-field nuclear magnetic resonance (LF-NMR).
- Development and validation of a thermo-hydro-mechanical (THM) multiphysics coupled numerical model against experimental data (error <5%).
Main Results:
- Increasing confining pressure compacts macropores/fractures and transforms micropores/mesopores, reducing permeability via a power-law relationship.
- Gas preferentially displaces free water from macropores/fractures at ΔP < 2 MPa; bound water displacement requires ΔP > 4 MPa.
- Field-scale simulations at 348 K indicate 150 m borehole spacing maximizes CBM productivity (8.3% higher daily yield than 200 m spacing) while ensuring safety.
Conclusions:
- Reveals intrinsic laws of gas-water two-phase seepage dominated by confining pressure in deep coal reservoirs.
- Demonstrates the critical role of confining pressure in controlling water displacement and permeability.
- Provides a validated quantitative basis for optimizing deep CBM extraction technologies and field development.
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