Chen Fangxuan, Ji Guang, Meng Dewei, Wang Guoting, Feng Naichao, Zheng Shuai, Huang Suqi, Shi Xiaomin, Li Yanrong
CNPC Research Institute of Petroleum Exploration & Development, Beijing 100083, China.
Development Department, PetroChina Changqing Oilfield Company, Xi'an, Shaanxi 710018, China.
ACS Omega. 2025 Aug 8;10(32):36310-36320. doi: 10.1021/acsomega.5c04400. eCollection 2025 Aug 19.
More than 50% of global coalbed methane (CBM) resources are estimated to reside in deep coal seams (depth >1500 m). The CBM retained in deep coal seams has higher free gas content with less formation water compared to the CBM in shallow coal seams, leading to different production methods. Current research has primarily addressed the shallow CBM extraction, with limited transferability to deep CBM (DCBM) reservoirs due to the distinct reservoir characteristics and occurrence state. In this work, we developed a slit-pore model to investigate the adsorption behaviors and production mechanisms of DCBM using molecular dynamics simulations. The slit-pore model includes a micropore, a macropore, and a fracture/cleat to simulate the flow unit of anthracite. We analyzed the adsorption patterns at different production stages and quantitatively evaluated the production performance of pressure-relief production and pressure-control production. DCBM components (CH, CH, N, and CO) are heterogeneously distributed in the multiscale model, with higher proportions of CH, CH, and CO in the micropore due to the high adsorption affinity and small molecular diameters. CH, CH, and CO exhibit monolayer adsorption in the micropore, and the production methods do not affect the adsorption pattern. Compared to the pressure-relief production, the pressure-control production yields higher DCBM production. The mass transfer from the macropore and the water-blocking effect in the micropore collectively constrain the fluid release from the micropore during pressure-relief production. This work provides a comprehensive understanding of the DCBM adsorption behaviors and production mechanisms.
据估计，全球超过50%的煤层气（CBM）资源存在于深部煤层（深度>1500米）中。与浅部煤层中的煤层气相比，深部煤层中保留的煤层气具有更高的游离气含量和更少的地层水，这导致了不同的开采方法。目前的研究主要集中在浅部煤层气的开采，由于储层特征和赋存状态不同，其对深部煤层气（DCBM）储层的可转移性有限。在这项工作中，我们开发了一个狭缝孔隙模型，利用分子动力学模拟研究DCBM的吸附行为和开采机理。狭缝孔隙模型包括一个微孔、一个大孔和一个裂隙/割理，以模拟无烟煤的流动单元。我们分析了不同开采阶段的吸附模式，并定量评估了降压开采和控压开采的生产性能。DCBM组分（CH、CH、N和CO）在多尺度模型中呈非均相分布，由于吸附亲和力高和分子直径小，微孔中CH、CH和CO的比例较高。CH、CH和CO在微孔中表现为单层吸附，开采方法不影响吸附模式。与降压开采相比，控压开采的DCBM产量更高。在降压开采过程中，大孔中的传质和微孔中的水锁效应共同限制了微孔中流体的释放。这项工作全面地理解了DCBM的吸附行为和开采机理。
