Shi Jihong, Gong Liang, Sun Shuyu, Huang Zhaoqin, Ding Bin, Yao Jun
College of New Energy, China University of Petroleum (East China) Qingdao 266580 China
Computational Transport Phenomena Laboratory, Division of Physical Science and Engineering, King Abdullah University of Science and Technology Thuwal 23955-6900 Saudi Arabia.
RSC Adv. 2019 Aug 13;9(44):25326-25335. doi: 10.1039/c9ra04963k.
Displacement of methane (CH) by injection gas is regarded as an effective way to exploit shale gas and sequestrate carbon dioxide (CO) simultaneously. To remarkably enhance the rupture and extension of fractures, an original and comprehensive simplification for the real shale composition model is established to study the shale gas displacement by gas injection. In the present model, besides the consideration in the existence of organic matter in shale, the choice of silica as inorganic minerals is firstly taken into account considering its brittleness characteristic to meet the demand of fracture stretch. Based on the model, the displacement methane process and competitive adsorption behaviors were studied by using the grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) respectively. As the results, the strong interaction between carbon dioxide and shale results in the higher efficiency of displacing methane. We also find that the optimum operating conditions for CO and N displacing methane are at the pore width of 30 Å, the result being slightly different from the previous studies indicating that the displacement efficiency of small pores is higher. Moreover, the displacement efficiency by using different gases can all reach higher than 50% when the injection pressure is greater than 30 MPa. It is expected that this work can reveal the mechanisms of competitive adsorption between shale gas and gases, and provide a guidance for displacement exploitation of shale gas by gas injection and sequestration of carbon dioxide.
通过注入气体置换甲烷（CH）被认为是一种同时开采页岩气和封存二氧化碳（CO₂）的有效方法。为了显著增强裂缝的破裂和扩展，建立了一种针对真实页岩组成模型的原始且全面的简化模型，以研究注气驱替页岩气的过程。在当前模型中，除了考虑页岩中有机质的存在外，首先考虑选择二氧化硅作为无机矿物，因其脆性特征可满足裂缝扩展的需求。基于该模型，分别采用巨正则蒙特卡罗（GCMC）和分子动力学（MD）方法研究了甲烷置换过程和竞争吸附行为。结果表明，二氧化碳与页岩之间的强相互作用导致甲烷置换效率更高。我们还发现，CO₂和N₂置换甲烷的最佳操作条件是在孔径为30 Å时，这一结果与之前表明小孔径置换效率更高的研究略有不同。此外，当注入压力大于30 MPa时，使用不同气体的置换效率均可达到50%以上。期望这项工作能够揭示页岩气与注入气体之间的竞争吸附机制，并为注气开采页岩气和封存二氧化碳提供指导。
