CO₂ geological sequestration in shale is a promising method to mitigate global warming caused by greenhouse gas emissions as well as to enhance the gas recovery to some degree, which effectively addresses the problems related to energy demand and climate change. With the data from the New Albany Shale in the Illinois Basin in the United States, the CMG-GEM simulator is applied to establish a numerical model to evaluate the feasibility of CO₂ sequestration in shale gas reservoirs with potential enhanced gas recovery (EGR). To represent the matrix, natural fractures, and hydraulic fractures in shale gas reservoirs, a multicontinua porous medium model will be developed. Darcy’s and Forchheimer’s models and desorption-adsorption models with a mixing rule will be incorporated into the multicontinua numerical model to depict the three-stage flow mechanism, including convective gas flow mainly in fractures, dispersive gas transport in macropores, and CH₄-CO₂ competitive sorption phenomenon in micropores. With the established shale reservoir model, different CO₂ injection schemes (continuous injection vs. pulse injection) for CO₂ sequestration in shale gas reservoirs are investigated. Meanwhile, a sensitivity analysis of the reservoir permeability between the hydraulic fractures of production and injection wells is conducted to quantify its influence on reservoir performance. The permeability multipliers are 10, 100, and 1,000 for the sensitivity study. The results indicate that CO₂ can be effectively sequestered in shale reservoirs. But the EGR of both injection schemes does not perform well as expected. In the field application, it is necessary to take the efficiency of supplemental energy utilization, the CO₂ sequestration ratio, and the effect of injected CO₂ on the purity of produced methane into consideration to design an optimal execution plan. The case with a permeability multiplier of 1,000 meets the demand for both CO₂ sequestration and EGR, which indicates that a moderate secondary stimulation zone needs to be formed between the primary hydraulic fractures of injection and production wells to facilitate the efficient energy transfer between interwell as well as to prevent CO₂ from channeling. To meet the demand for CO₂ sequestration in shale gas reservoirs with EGR, advanced and effective fracking is essential.

中文翻译：

---

页岩气藏二氧化碳封存与提高采气率的数值模拟与建模

页岩中CO ₂地质封存是缓解温室气体排放导致的全球变暖以及在一定程度上提高天然气采收率的一种很有前景的方法，有效解决了能源需求和气候变化相关问题。以美国伊利诺伊盆地新奥尔巴尼页岩数据为基础，应用CMG-GEM模拟器建立数值模型，评价CO ₂的可行性页岩气藏中的封存具有潜在的提高天然气采收率（EGR）。为了表示页岩气藏中的基质、天然裂缝和水力裂缝，将开发多连续体多孔介质模型。将 Darcy 和 Forchheimer 模型以及带混合规则的解吸-吸附模型纳入多连续体数值模型，描述三级流动机制，包括主要在裂缝中的对流气流、大孔隙中的弥散气体输运和 CH ₄ -CO ₂微孔中的竞争吸附现象。与所建立的页岩储层模型，不同的CO ₂注射方案（连续喷射脉冲与注射）用于CO ₂研究了页岩气藏中的封存。同时，对生产井和注入井的水力裂缝之间的储层渗透率进行敏感性分析，以量化其对储层性能的影响。敏感性研究的渗透率乘数为 10、100 和 1,000。结果表明，CO ₂可以有效地隔离在页岩储层中。但是两种喷射方案的 EGR 都没有达到预期的效果。在现场应用中，需要综合考虑补充能源利用效率、CO ₂封存率、注入CO _{2 的影响}生产甲烷的纯度考虑以设计最佳执行计划。渗透系数为1000的案例同时满足了CO ₂封存和EGR的需求，这表明注采井主要水力压裂裂缝之间需要形成中等程度的二次增产带，以促进井间能量的有效传递。以及防止CO ₂窜流。为了满足EGR页岩气藏CO ₂封存的需求，先进有效的压裂技术必不可少。