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Investigating the effects of gas type and operation mode in enhanced gas recovery in unconventional reservoirs
Gas Science and Engineering ( IF 5.285 ) Pub Date : 2018-02-01 , DOI: 10.1016/j.jngse.2017.12.001
C.J.S. Santiago , A. Kantzas

Abstract A model that combines the Dusty-Gas approach and Darcy's Law is used to investigate the dynamics of production enhancement by gas injection in unconventional reservoirs. A comparison between CH4, N2 and CO2 injection in both Huff-n-Puff and Flooding operation modes is performed. The mechanism of production enhancement for each gas is different. CO2 can be injected to preferentially adsorb into the shale matrix, releasing hydrocarbons. In this case, the dominant mechanism is competitive adsorption. Due to stronger affinity with adsorption sites, CO2 injection would suggest high cumulative production. In spite of that, frontal displacement is very slow in this case, resulting in poorer short-term production when compared to N2 and CH4. N2 injection induces the release of hydrocarbons solely by partial pressure reduction. Frontal velocities are fast, resulting in high short-term production. Yet, since N2 is deemed inert, it does not replace components retained in the adsorbed phase. CH4 injection also prompts desorption of heavier hydrocarbons by partial pressure reduction. However, as heavier fractions are desorbed, CH4 molecules occupy the vacant sites. In this case, combined mechanisms of partial pressure reduction and uptake by the adsorption sites results in efficient release of heavier hydrocarbons. In this work, we demonstrate the impact of the presence of heavier hydrocarbon fractions in modeling gas transport during enhanced gas recovery processes. Multicomponent gas flow affects average reservoir pressure, produced gas composition and natural gas liquids (NGLs) yields, which is relevant for development of wet-gas and dry-gas unconventional reservoirs. Moreover, we demonstrate that injection gas composition significantly influences transport behavior of chemical species through the porous medium, and we highlight the relevant transport mechanisms during enhanced gas recovery in tight reservoirs.

中文翻译:

非常规油气藏气类型和作业方式对提高采气率的影响研究

摘要 采用Dusty-Gas方法和Darcy定律相结合的模型研究非常规油藏注气增产动态。对 Huff-n-Puff 和 Flooding 操作模式下的 CH4、N2 和 CO2 注入进行了比较。每种气体的增产机制不同。可以注入 CO2 以优先吸附到页岩基质中,释放出碳氢化合物。在这种情况下,主要机制是竞争吸附。由于与吸附位点的亲和力更强,因此注入 CO2 表明累积产量较高。尽管如此,在这种情况下,锋面位移非常缓慢,与 N2 和 CH4 相比,导致短期生产较差。N 2 注入仅通过分压降低引起碳氢化合物的释放。锋面速度很快,导致短期产量高。然而,由于 N2 被认为是惰性的,它不能替代保留在吸附相中的组分。CH4 注入还通过分压降低促进较重烃的解吸。然而,随着较重的馏分被解吸,CH4 分子占据空位。在这种情况下,分压降低和吸附位点吸收的组合机制导致重烃的有效释放。在这项工作中,我们证明了重质烃馏分的存在对增强气体采收率过程中模拟气体传输的影响。多组分气流影响平均储层压力、产出气成分和天然气液体 (NGL) 产量,这与湿气和干气非常规储层的开发有关。
更新日期:2018-02-01
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