超临界 CO2 突破水桥并提高页岩油采收率：分子动力学模拟研究,Energy & Fuels

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超临界 CO2 突破水桥并提高页岩油采收率：分子动力学模拟研究
Energy & Fuels ( IF 5.2 ) Pub Date : 2022-07-07 , DOI: 10.1021/acs.energyfuels.2c01547
Bing Liu ₁ , Wenyu Liu ₁ , Zhiming Pan ₁ , Leyang Yu ₁ , Zhiyang Xie ₁ , Guangzhong Lv ₂ , Peihe Zhao ₁ , Dongmeng Chen ₁ , Wenjing Fang ₁

Affiliation

CO ₂注入已被证明是最有前景的页岩油藏提高采收率（EOR）方法。页岩纳米孔中阻碍油流的水桥对CO ₂ -EOR有显着影响，而这种影响的微观机制尚不清楚，严重阻碍了CO ₂注入技术的设计。在这项工作中，分子动力学模拟用于研究将 CO ₂注入油水桥共存的页岩纳米孔后流体传输的微观过程。我们的结果证实，CO ₂可以突破页岩纳米孔中的水桥，形成流体通道，提高原油的流动性和采收率。整个过程可分为三个阶段：（i）CO ₂在浓度梯度下向纳米孔扩散，油向裂缝扩散；(ii) CO ₂突破水桥；(iii) CO ₂在压力梯度下将油驱出纳米孔。_{此外，总结了CO 2}突破水桥的四种主要微观机制：（i）水分子在水桥中的“多孔”分布；(ii) 水桥中心的氢键越来越少；(iii) CO ₂冲洗水桥；(iv) CO ₂通过氢键拖动水分子。_{最后，在压力驱和CO 2}与原油互扩散的协同作用下，总采收率不断提高。值得注意的是，需要对CO ₂注入和关井进行适当调节，以避免由于连续压力驱使采收油回注到纳米孔中。CO ₂注入引起油的膨胀，增加了油的流动性，水桥突破后可进一步增强。我们的研究结果促进了对含水页岩储层CO _{2 -EOR 微观机理的理解和非常规资源的开发。}

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Supercritical CO2 Breaking Through a Water Bridge and Enhancing Shale Oil Recovery: A Molecular Dynamics Simulation Study

CO₂ injection has been proved to be the most promising enhanced oil recovery (EOR) method for shale reservoirs. Water bridges impeding oil flow in shale nanopores have a significant impact on CO₂-EOR, and the microscopic mechanism of this effect is still unclear, seriously hindering the design of CO₂ injection technologies. In this work, molecular dynamics simulations were employed to study the microscopic process of fluid transport following CO₂ injection into shale nanopores where oil and a water bridge coexist. Our results confirm that CO₂ can break through the water bridge in shale nanopores to form fluid channels and improve the mobility and recovery of crude oil. The whole process can be divided into three stages: (i) CO₂ diffuses into the nanopore, while oil diffuses into the fracture under concentration gradient; (ii) CO₂ breaks through the water bridge; and (iii) CO₂ drives oil out of the nanopore under a pressure gradient. Furthermore, four major microscopic mechanisms of CO₂ breaking through a water bridge are summarized: (i) “porous” distribution of water molecules in the water bridge; (ii) less and weaker hydrogen bonds in the center of the water bridge; (iii) CO₂ flushing the water bridge; and (iv) CO₂ dragging water molecules through hydrogen bonding. Finally, the total oil recovery factor keeps increasing in the synergy of pressure flooding and interdiffusion of CO₂ and oil. It is worth noting that CO₂ injection and shut-in need to be properly regulated to avoid the reinjection of recovered oil into the nanopore owing to continuous pressure flooding. CO₂ injection induces the swelling of oil and increases the mobility of oil, which can be further enhanced after the breakthrough of the water bridge. Our results advance the understanding of the microscopic mechanism of CO₂-EOR of water-bearing shale reservoirs and the exploitation of unconventional resources.

更新日期：2022-07-07

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