Molecular insights of condensate trapping mechanism in shale oil reservoirs and its implications on lean gas enhanced oil recovery
Molecular insights of condensate trapping mechanism in shale oil reservoirs and its implications on lean gas enhanced oil recovery
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DOI：
10.1016/j.cej.2023.146366
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发表时间：
2023-09
影响因子：
15.1
通讯作者：
Shihao Wang;Hongwei Zhang;Bikai Jin;Rui Qiao;Xianhuan Wen
中科院分区：
文献类型：
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作者：
Shihao Wang;Hongwei Zhang;Bikai Jin;Rui Qiao;Xianhuan Wen
非均质孔隙结构和狭窄孔隙空间的限制作用导致了非常规油气藏中烃类的差异释放/滞留现象。到目前为止，这一现象的机理，特别是动态过程，需要进一步研究，因为它影响到气基提高石油采收率（EOR）操作的设计。本文采用分子动力学模拟的方法，建立了一个两浴模型，其中两个浴用于模拟体孔，一个连接两个浴的纳米通道用于模拟孔喉，并对导致差异释放现象的毛细冷凝物捕获机制进行了数值研究。甲烷（C1）和癸烷（C10）分子用于代表原位油的轻质和重质组分。分子动力学结果表明，在一次衰竭初期，轻组分释放速度快于重组分，导致体系泡点以上的气油比（戈尔）增加。随着耗尽的继续，由于限制效应，较重的烃在纳米通道中积累，而轻质烃倾向于保留在死端孔中。在气体提高采收率过程中，注入气体溶解了纳米通道中的液体，从而提高了“被困”烃类的采收率。我们证明，大量的轻烃可能被“困”在非常规油藏的主要枯竭，由于毛细管凝析油捕获效应。通过注气可以部分回收被困烃类。我们的研究对实际的EOR操作具有指导意义。
The heterogeneous pore structure and the confinement effect of the narrow pore space lead to the differential release/retention phenomenon of hydrocarbons in unconventional reservoirs. So far, the mechanism of this phenomenon, in particular the dynamic process, requires further investigation since it affects the design of gas-based enhanced oil recovery (EOR) operations. In this work, we aim to numerically study the capillary condensate trapping mechanism that causes the differential release phenomenon by conducting molecular dynamics (MD) simulations.In our work, a two-bath MD model is set up, in which two baths are used to mimic the bulk pores and a nano-channel connecting the two baths is used to model the pore throat. Methane (C1) and decane (C10) molecules are used to represent the light and heavy component of the in-situ oil. The MD results show that at the early stage of the primary depletion, the light components release faster than the heavier components, leading to increasing gas oil ratio (GOR) above the system’s bubble point. As depletion continues, heavier hydrocarbons accumulate in the nano-channel due to the confinement effect, while light hydrocarbons tend to remain in the dead-end pores. During the gas EOR process, the injected gas ‘dissolves’ the liquid in the nano-channel and thus enhances the recovery of the ‘trapped’ hydrocarbons.This work systematically investigates the impact of pore throat on the differential release and trapping effect. We demonstrate that a significant amount of light hydrocarbons may be ‘trapped’ during the primary depletion of unconventional reservoirs, due to the capillary condensate trapping effect. The trapped hydrocarbons can be partly recovered through gas injection. Our study has implications for practical EOR operations.