Study and application of active pressure-control production method for coal-rock gas wells

doi:10.3969/j.issn.1672-7703.2025.06.013

Abstract

Abstract: Compared with shallow–middle coal seams, deep coal reservoirs exhibit significant differences in gas–water occurrence, production mechanism, and engineering response. In the in-situ high-pressure deep formations, free gas mainly flows through continuous media. The variations in reservoir pressure and bottom-hole flowing pressure directly influence gas–water distribution, migration driving force, and production capacity change law. Therefore, a rational pressure-control regime enhances gas flow and production capacity. Based on the control of pressure evolution on coal-rock gas migration mechanism, an active pressure release and production control method centered on differentiated bottom-hole pressure regulation has been proposed. By establishing a critical fracturing fluid pressure difference model, criteria for iso-flow and iso-pressure point recognition, and a dynamic gas–water ratio identification model, this approach reveals the fluid migration characteristics and pressure difference control rules across different production stages, and forms a staged bottom-hole pressure control system, that is, “safe open flow–steady water drainage–coordinated gas production–enhanced and steady gas production”, achieving dynamic matching of pressure system with flow mechanism and desorption kinetics in the whole production process. Numerical simulations of typical coal-rock wells in the eastern margin of Ordos Basin confirm that the active pressure-control strategy enables to gradually release and effectively utilize reservoir energy, achieving a “multi-peak” growth of gas production profile, with the predicted recovery factor increased by approximately 8.9% compared with non-production-control regime. Field tests further demonstrate that the staged and graded pressure release effectively slows the pressure decline, mitigates rapid gas–water ratio increase, maintains two-phase flow balance, and gradually releases production capacity, significantly enhancing single-well capacity and steady-production duration. The study results provide a theoretical basis and engineering guidance for high-efficiency development of coal-rock gas in Ordos Basin.

Key words: Ordos Basin, coal-rock gas, active pressure release, iso-flow point, gas–water ratio, numerical simulation

CLC Number:

TE377

Deng Ze, Zhao Qun, Li Cong, Ma Limin, Zhang Lei, Ding Rong, Fei Shixiang, Huang Daojun, Huang Jinxiu, Wang Shuhui, Zhang Xianmin. Study and application of active pressure-control production method for coal-rock gas wells[J]. China Petroleum Exploration, 2025, 30(6): 185-200.

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