Mechanisms behind the controlling effects of temperature-pressure conditions on the dynamic CH₄–H₂O production from bituminous coal

Authors

ZHANG Hewei, Key Laboratory of Coalbed Methane Resources & Reservoir Formation Process, Ministry of Education, China University ofMining and Technology, Xuzhou 221008, China; School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, ChinaFollow
SHEN Jian, Key Laboratory of Coalbed Methane Resources & Reservoir Formation Process, Ministry of Education, China University ofMining and Technology, Xuzhou 221008, China; School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, ChinaFollow
LI Kexin, Shanxi CBM Branch Company, Huabei Oilfield Company, PetroChina, Changzhi 046000, China
WU Caifang, Key Laboratory of Coalbed Methane Resources & Reservoir Formation Process, Ministry of Education, China University ofMining and Technology, Xuzhou 221008, China; School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China

Abstract

Background For deep coalbed methane (CBM) exploitation, the temperature-pressure synergistic effect in the CH₄-H₂O two-phase flow remains poorly understood, restricting the establishment of efficient CBM production systems.Methods This study investigated the No.13 coal seam in the Guanjiaya Coal Mine along the eastern margin of the Ordos Basin. Using low-field nuclear magnetic resonance (LF-NMR) and nuclear magnetic resonance imaging (NMRI) techniques, this study explored the dynamic process of CH₄ displacing water and associated gas-water production mechanisms under different displacement pressures (2‒8 MPa) and temperatures (25 ℃ and 60 ℃).Results and Conclusions The sample used in this study primarily exhibited micropores and mesopores, as well as strongly heterogeneous water distribution, which was jointly controlled by the pore-fracture system and bedding structure. Under displacement at the normal temperature (25 ℃), the NMR signals showed significant non-monotonic variations with increasing displacement pressure and time. Under a displacement pressure of 2 MPa, the gas-water saturation decreased significantly, with water drained rapidly from macropores. Under displacement pressures of 4 MPa and 6 MPa, the gas-water saturation increased abnormally, which was primarily attributed to methane adsorption. As the displacement pressure increased to 8 MPa, the gas-water saturation decreased again. The NMRI images reveal that the gas and water advanced along the gas injection direction and subsequently converged toward the central axis of the sample, gradually forming a zonal distribution characterized by gas saturation at the injection end, gas-water coexistence in the middle section, and residual water at the outlet. Under displacement at a high temperature of 60 ℃, the gas-water saturation decreased more significantly (16.67%) compared to that (11.2%) under normal-temperature displacement. In this case, no intensified NMR signal was observed at displacement pressures of 4 MPa and 6 MPa, indicating that high temperature inhibited methane adsorption and retention at moderate pressures. However, intensified NMR signals were identified under a displacement pressure of 8 MPa, revealing a shift toward the re-enhancement of methane adsorption capacity under high pressure. Further analysis indicates that the nonlinear CH₄-H₂O flow represents a pressure-driven, complex dynamic process that couples pore structure responses, methane adsorption and expansion, interfacial mass transfer, and flow in multi-scale pores. Therefore, in deep CBM exploitation, it is necessary to properly regulate the production pressure difference to avoid severe water blocking. Meanwhile, the temperature effect should be considered to achieve efficient gas-water production. For reservoirs with a temperature of approximately 60 ℃, it is advisable to control the production pressure difference at 4−6 MPa during the initial production stage. The results of this study provide an experimental reference and theoretical basis for selecting the pressure difference in deep CBM production.

Keywords

gas-water production, nuclear magnetic resonance imaging (NMRI), pore structure, dynamic mechanism, Ordos basin

DOI

10.12363/issn.1001-1986.25.08.0660

Recommended Citation

ZHANG Hewei, SHEN Jian, LI Kexin, et al. (2026) "Mechanisms behind the controlling effects of temperature-pressure conditions on the dynamic CH₄–H₂O production from bituminous coal," Coal Geology & Exploration: Vol. 54: Iss. 3, Article 7.
DOI: 10.12363/issn.1001-1986.25.08.0660
Available at: https://cge.researchcommons.org/journal/vol54/iss3/7

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