Abstract In addition to CO2-CH4 interactions (Part 1), the success of CO2 enhanced coalbed methane (CO2-ECBM) and geological sequestration are significantly affected by the CO2-H2O wettability. Wettability controls both gas desorption and transport and is influenced by injection pressure, reservoir temperature and the state of water that is present – as either adsorbed- or free-water. Dynamic changes in wettability remains poorly constrained – due to the innate difficulty and invasive nature of conventional measurements (e.g., captive gas bubble and pendent drop tilted plate methods). In part 2, we use nuclear magnetic resonance (NMR) as a non-invasive method to explore the mechanisms of these factors (pressure, temperature, water-state) on CO2-H2O wettability during CO2-ECBM. Results for contrasting subbituminous coal and anthracite show that the CO2 wettability of coals significantly increases with increasing CO2 injection pressure up to 5 MPa before stabilizing to a limiting value. This suggests that the most economically-suitable injection pressure is ~5 MPa. CO2 wettability also increases with a decrease in temperature suggesting that shallower reservoirs may be marginally improved in this trend. Additionally, the presence of non-adsorbed water in coals significantly reduces both the sensitivity of CO2 wettability to pressure and the absolute magnitude of wettability relative to the case where free-water is absent. Thus, draining free-water from the reservoir will serve the dual purposes of both increasing gas transport and the potential for desorption from the perspective of CO2-H2O wettability. The far-reaching results in this study, together with the companion paper (Part 1) are significant for evaluating CO2-ECBM improvement both in enhancing methane recovery and CO2 utilization in coals.

中文翻译：

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煤层中 CO2-ECBM 和 CO2 封存期间的动态流体相互作用 第 2 部分：CO2-H2O 润湿性

摘要 除了 CO2-CH4 相互作用（第 1 部分），CO2 增强煤层气 (CO2-ECBM) 和地质封存的成功受 CO2-H2O 润湿性的显着影响。润湿性控制气体解吸和输运，并受注入压力、储层温度和存在的水状态（吸附水或游离水）的影响。由于传统测量的先天困难和侵入性（例如，俘获气泡和悬滴倾斜板方法），润湿性的动态变化仍然受到很大限制。在第 2 部分中，我们使用核磁共振 (NMR) 作为一种非侵入性方法来探索这些因素（压力、温度、水状态）对 CO2-ECBM 过程中 CO2-H2O 润湿性的机制。对比次烟煤和无烟煤的结果表明，在稳定到极限值之前，煤的 CO2 润湿性随着 CO2 注入压力的增加而显着增加，最高可达 5 MPa。这表明最经济合适的注射压力是~5 MPa。CO2 润湿性也随着温度的降低而增加，这表明在这种趋势下，较浅的储层可能会略有改善。此外，煤中非吸附水的存在显着降低了 CO2 润湿性对压力的敏感性和相对于不存在自由水的情况下润湿性的绝对量级。因此，从 CO2-H2O 润湿性的角度来看，从储层中排出游离水将起到增加气体传输和解吸潜力的双重目的。