Reasonable start time of carbon dioxide injection in enhanced coalbed methane recovery involving thermal-hydraulic-mechanical couplings  

作　　者：Chaojun FAN Lei YANG Bin XIAO Lijun ZHOU Haiou WEN Hao SUN 

机构地区：[1]College of Mining,Liaoning Technical University,Fuxin 123000,China [2]College of Safety Science and Engineering,Liaoning Technical University,Huludao 125105,China

出　　处：《Frontiers of Earth Science》2023年第3期832-843,共12页地球科学前沿（英文版）

摘　　要：Injection of gas (CO_(2)) into coal seams is an effective method to benefit from both CO_(2) geological storage and coalbed methane recovery. Based on the dual pore structure of coal mass, and the Weibull distribution of fracture permeability, a menmal-hydraulic-mechanical (THM) coupling mathematical model is proposed involving the non-isothermal adsorption of binary gases, dynamic gas diffusion between matrix and fractures, multiphase seepage, coal deformation, heat conduction and heat convection. This mathematical model is applied to study the process of CO_(2)-enhanced coalbed methane recovery (CO_(2)-ECBM). Results show that the CH4 content of CO_(2)-ECBM in coal seam decreases significantly when compared with that of regular drainage, and decreases rapidly in the early stage but slowly in the later stage. Coal seam permeability evolution is triggered by changes in gas adsorption/desorption, temperature and effective stress. For regular drainage, the early permeability shows a decreasing trend dominated by the increase of effective stress, while the later permeability shows an increasing trend dominated by the CH4 desorption caused shrinkage of coal matrix. For CO_(2)-ECBM, the permeability in coal seam generally shows a downward trend due to both matrix swelling induced by gas adsorption and thermal expansion, particularly near injection well. There appears an increased and delayed peak production rate of CH4. The CH4 production rate of CO_(2)-ECBM is always higher than that of regular drainage. The CH4 cumulative production and CO_(2) cumulative storage linearly increase with time, and the CH4 cumulative production of CO_(2)-ECBM increased by 39.2% in the duration of 5000 d compared with regular drainage. Reasonable CO_(2) injection starting time can overcome the issue of early CO_(2) breakthrough and ineffective increase of CH4 production. In the studied case, the optimal injection starting time is 2500 d. Compared with the simultaneous CH4 extraction and CO_(2) injection, the CH4 cumulative production of

关 键 词：CO_(2)sequestration coalbed methane reasonable injection start time thermo-hydro-mechanical coupling model numerical simulation 

分 类 号：TE3[石油与天然气工程—油气田开发工程]