Sedghi Mohammad, Piri Mohammad, Goual Lamia
Department of Petroleum Engineering, University of Wyoming , 1000 East University Avenue, Laramie, Wyoming 82071, United States.
Langmuir. 2016 Apr 12;32(14):3375-84. doi: 10.1021/acs.langmuir.5b04713. Epub 2016 Apr 1.
Unconventional reservoirs such as hydrocarbon-bearing shale formations and ultratight carbonates generate a large fraction of oil and gas production in North America. The characteristic feature of these reservoirs is their nanoscale porosity that provides significant surface areas between the pore walls and the occupying fluids. To better assess hydrocarbon recovery from these formations, it is crucial to develop an improved insight into the effects of wall-fluid interactions on the interfacial phenomena in these nanoscale confinements. One of the important properties that controls the displacement of fluids inside the pores is the threshold capillary pressure. In this study, we present the results of an integrated series of large-scale molecular dynamics (MD) simulations performed to investigate the effects of wall-fluid interactions on the threshold capillary pressures of oil-water/brine displacements in a calcite nanopore with a square cross section. Fully atomistic models are utilized to represent crude oil, brine, and calcite in order to accommodate electrostatic interactions and H-bonding between the polar molecules and the calcite surface. To this end, we create mixtures of various polar and nonpolar organic molecules to better represent the crude oil. The interfacial tension between oil and water/brine and their contact angle on calcite surface are simulated. We study the effects of oil composition, water salinity, and temperature and pressure conditions on these properties. The threshold capillary pressure values are also obtained from the MD simulations for the calcite nanopore. We then compare the MD results against those generated using the Mayer-Stowe-Princen (MSP) method and explain the differences.
非常规油藏，如含烃页岩地层和超致密碳酸盐岩，在北美油气产量中占很大比例。这些油藏的特征是其纳米级孔隙度，在孔隙壁和占据流体之间提供了显著的表面积。为了更好地评估这些地层中的烃类采收率，深入了解壁 - 流体相互作用对这些纳米级受限空间内界面现象的影响至关重要。控制孔隙内流体驱替的重要性质之一是阈毛细管压力。在本研究中，我们展示了一系列大规模分子动力学（MD）模拟的结果，这些模拟旨在研究壁 - 流体相互作用对方解石纳米孔（方形横截面）中油水/盐水驱替阈毛细管压力的影响。使用全原子模型来表示原油、盐水和方解石，以适应极性分子与方解石表面之间的静电相互作用和氢键。为此，我们创建了各种极性和非极性有机分子的混合物，以更好地表示原油。模拟了油与水/盐水之间的界面张力及其在方解石表面的接触角。我们研究了油的组成、水的盐度以及温度和压力条件对这些性质的影响。还从方解石纳米孔的MD模拟中获得了阈毛细管压力值。然后，我们将MD结果与使用迈耶 - 斯托 - 普林森（MSP）方法生成的结果进行比较，并解释其中的差异。
