Soaking in CO2 huff-n-puff: A single-nanopore scale study
Soaking in CO2 huff-n-puff: A single-nanopore scale study
复制标题
DOI：
10.1016/j.fuel.2021.122026
复制
发表时间：
2021-09-27
期刊：
影响因子：
7.4
通讯作者：
Qiao, Rui
中科院分区：
文献类型：
--
作者：
Moh, Do Yoon;Zhang, Hongwei;Qiao, Rui
CO2吞吐是一种很有前途的提高非常规油藏采收率和封存CO2的方法。优化Huff-n-Puff的运行需要对纳米孔中二氧化碳和石油的热力学和传输现象有基本的了解。在这里，我们用分子动力学模拟方法研究了CO2在一个4 nm宽的方解石孔中的浸泡步骤。我们发现，进入孔洞的二氧化碳分子可以吸附在孔壁上，并沿着孔壁扩散，或者作为自由二氧化碳分子输送到孔洞内部。正十一烷分子从孔壁中置换出来，并离开孔中的体积区。在到达孔的末端之前，吸附的和自由的CO2分子在孔内的密度前锋的运动服从t(1/2)标度律，有效扩散系数比整体CO2的有效扩散系数小50%。除浸泡初期外，吸附和游离二氧化碳分子的积累速度相似，并遵循扩散标度定律。这些孔隙尺度的结果突出了在非常规油藏的浸泡过程中，表面吸附在二氧化碳储存和运输中的重要性。
CO2 Huff-n-Puff is a promising method for enhancing the oil recovery from unconventional reservoirs and sequestering CO2. Optimizing the operation of Huff-n-Puff requires a fundamental understanding of the thermodynamic and transport phenomena of CO2 and oil in nanopores. Here, we investigate the soaking step of CO2 Huff-n-Puff in a single, 4 nm-wide calcite pore using molecular dynamics simulations. We show that the CO2 molecules entering the pore can become adsorbed on pore walls and diffuse along with walls or are transported into the pore's interior as free CO2 molecules. Decane molecules are displaced from the pore walls and out of the bulk zone in the pore. Before reaching the pore's end, the movement of the density fronts of adsorbed and free CO2 molecules inside the pore obeys a t(1/2) scaling law with effective diffusion coefficients similar to 50% smaller than that of bulk CO2. Except at the very beginning period of soaking, the accumulation of adsorbed and free CO2 molecules occurs at a similar rate and follows the diffusive scaling law. These pore-scale results highlight the importance of surface adsorption in the storage and transport of CO2 during the soaking process in unconventional oil reservoirs.