Low salinity effect on the recovery of oil trapped by nanopores: A molecular dynamics study
Low salinity effect on the recovery of oil trapped by nanopores: A molecular dynamics study
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DOI：
10.1016/j.fuel.2019.116443
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发表时间：
2020-02
期刊：
影响因子：
7.4
通讯作者：
Chao Fang;Yafan Yang;Shuyu Sun;R. Qiao
中科院分区：
文献类型：
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作者：
Chao Fang;Yafan Yang;Shuyu Sun;R. Qiao
低矿化度水驱（LSW）是许多油藏提高采收率的有效方法，其成功归因于一系列低矿化度效应。在这项工作中，我们进行了分子动力学模拟，以研究通过降低储层盐度来回收被纳米孔捕获的石油的可行性。油最初被一个狭缝纳米孔捕获，一部分油从孔入口处突出。当储层盐度降低后，将油和孔隙壁分开的盐水薄膜变得更厚，从而将一些被困的油驱出孔隙。我们量化了这一过程的自由能分布，并阐明了潜在的分子机制。有趣的是，盐水膜的生长主要是由水从盐水储层输送到孔隙中，而不是由盐水膜中离子的耗尽所决定的。这些结果提供了分子证据，证明低盐度盐水有利于纳米孔捕获的石油的开采。他们强调，当盐膜的离子耗竭受到抑制时，水的渗透作用可以在盐膜的膨胀中发挥根本作用；因此，提高了石油采收率。水通过盐水薄膜的缓慢渗透，从而导致油从孔隙中缓慢排出，这可能有助于解释LSW微观模拟实验中报道的异常缓慢的石油采收率。
Low salinity waterflooding (LSW) is an effective method for enhancing the oil recovery from many reservoirs, and its success has been traced to a host of low salinity effects. In this work, we perform molecular dynamics simulations to study the feasibility of recovering oil trapped by nanopores by lowering the reservoir salinity. The oil is initially trapped by a slit nanopore, with a portion of the oil protruding from the pore entrance. After the reservoir salinity is lowered, the thin brine films that separate the oil and pore walls become thicker to drive some of the trapped oil out of the pore. We quantify the free energy profile of this process and clarify the underlying molecular mechanisms. Interestingly, the brine film growth is dominated by the water transport from the brine reservoir into the pore rather than by the depletion of ions from the brine film. These results provide molecular evidence that low salinity brines benefit the recovery of the oil trapped by nanopores. They highlight that when ion depletion from thin brine films is suppressed, the osmosis of water can play a fundamental role in the expansion of the brine films; thus, the enhanced oil recovery. The slow osmosis of water through thin brine films and thus the slow displacement of oil from the pore may help explain the anomalously slow oil recovery reported in micro-modeling experiments of LSW.