Gong Shengli, Zhang Lu, Zhang Tongyao, He Wei, Hu Weiqiang, Yin Hongchao, Ma Liangshuai, Hong Xin, Zhang Wei, Zhang Bo
EnerTech-Drilling&Production Co., China National Offshore Oil Corporation, Tianjin, 300452, China.
Heliyon. 2024 Jul 25;10(15):e34818. doi: 10.1016/j.heliyon.2024.e34818. eCollection 2024 Aug 15.
CH production rate of coalbed methane (CBM) well decreases rapidly during primary recovery in the deeply buried coal seam, resulting in a lot of CH residues. CO pour into deep coal seam with high stress sensitivity is available for enhancing CH recovery by improving permeability for reservoir fracture and displacing CH adsorbed in matrix. A coupled adsorp-hydro-thermo-mechanical (AHTM) model for deep methane development is established by considering the coupling relationships of non-isothermal and non-constant pressure competitive adsorption between CO and CH, multi-phase flow, unsteady diffusion, heat transmission and in-situ stress variety. The model is verified by historical production and then used for CO enhanced CBM (CO-ECBM) of deep coal reservoir in a sedimentary basin in Northwest China. The simulation results show that: (1) For primary recovery, permeability in coal reservoir drops rapidly with the development of CBM, which seriously restricts the production of CH. The permeability of the reservoir decreases from 7.89 × 10 m to less than 1.50 × 10 m, CH production rate in CBM well reduces to below 2000 m/d, and the average total CH content of coal reservoir is reduced by 5.49 m/t with the decrease of only 1.12 m/t of average adsorbed CH in a production duration of 2000 d (2) With 10 MPa CO continuous injection into coal seam after 700d of primary, the permeability for reservoir and CH production rate increase while the total CH content and adsorption CH content in reservoir decrease compared with the primary recovery. (3) CO pouring into coal reservoir increases the CH production time and rate, which improves CH recovery of coal reservoir. And it increases by 23.36 %, 23.07 % and 22.46 % with shut-in thresholds of CH production rate of 1000 m/d, 800 m/d and 600 m/d, respectively. The investigation is of great significance for the development of deep coalbed methane.
在深埋煤层的一次采气过程中，煤层气（CBM）井的CH产量迅速下降，导致大量CH残留。将具有高应力敏感性的CO注入深部煤层，可通过改善储层裂缝渗透率和驱替吸附在基质中的CH来提高CH采收率。考虑CO与CH的非等温、非恒压竞争吸附、多相流、非稳态扩散、热传导和原地应力变化的耦合关系，建立了深部煤层气开发的吸附-热-流-固耦合（AHTM）模型。通过历史生产数据对该模型进行了验证，然后将其应用于中国西北某沉积盆地深部煤储层的CO强化煤层气（CO-ECBM）开采。模拟结果表明：（1）一次采气过程中，煤储层渗透率随煤层气开发迅速下降，严重制约了CH的产量。储层渗透率从7.89×10 m降至小于1.50×10 m，煤层气井CH产量降至2000 m/d以下，在2000 d的生产期内，煤储层平均总CH含量降低了5.49 m/t，而平均吸附CH仅降低了1.12 m/t；（2）一次采气700 d后，向煤层连续注入10 MPa的CO，与一次采气相比，储层渗透率和CH产量增加，而储层总CH含量和吸附CH含量降低；（3）向煤储层注入CO增加了CH生产时间和产量，提高了煤储层CH采收率。当CH产量关井阈值分别为1000 m/d、800 m/d和600 m/d时，采收率分别提高了23.36%、23.07%和22.46%。该研究对深部煤层气开发具有重要意义。
