Abstract The study of transport properties of unconventional oil reservoirs such as shale gas is crucial to optimize production, enhance oil extraction, and decrease costs and environmental hazards. One important dynamical property of fluids is diffusion, which is necessary to determine the oil mobility and rate of oil production from the reservoir, and can be obtained through the self-diffusion coefficient. To obtain the transport properties of fluids under confinement, one must take into account the surface and the confinement effects. Moreover, approaches that consider the position-dependency and the nonlinear particle distribution are required. Applying methods based on probability density function, the self-diffusion components of methane-ethane mixtures confined within calcite nanopores were calculated, using molecular dynamics simulations. The anisotropy between x x , y y , and z z components of the self-diffusion tensor has different effects depending on the position inside the nanopore. A surface effect causes an anisotropic behavior between parallel self-diffusion coefficients for this mixture close to the calcite walls. At the center of the pore, the confinement effect is manifested by lowering the value of the perpendicular self-diffusion coefficient when compared to the parallel ones. Mixture composition plays an important role, since a higher ethane content shows greater anisotropy between parallel components.

中文翻译：

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方解石纳米孔内甲烷-乙烷混合物自扩散系数的表面和限制效应

摘要 研究页岩气等非常规油藏输运特性对于优化生产、提高石油开采量、降低成本和减少环境危害至关重要。流体的一项重要动力学特性是扩散，它是确定油藏的石油流动性和产油速率所必需的，可以通过自扩散系数获得。为了获得约束条件下流体的传输特性，必须考虑表面和约束效应。此外，需要考虑位置相关性和非线性粒子分布的方法。应用基于概率密度函数的方法，使用分子动力学模拟计算了限制在方解石纳米孔内的甲烷-乙烷混合物的自扩散成分。自扩散张量的 xx 、 yy 和 zz 分量之间的各向异性根据纳米孔内的位置具有不同的影响。表面效应导致这种靠近方解石壁的混合物的平行自扩散系数之间的各向异性行为。在孔的中心，与平行的相比，通过降低垂直自扩散系数的值来体现限制效应。混合物组成起着重要作用，因为较高的乙烷含量表明平行组分之间的各向异性更大。表面效应导致这种靠近方解石壁的混合物的平行自扩散系数之间的各向异性行为。在孔的中心，与平行的相比，通过降低垂直自扩散系数的值来体现限制效应。混合物组成起着重要作用，因为较高的乙烷含量表明平行组分之间的各向异性更大。表面效应导致这种靠近方解石壁的混合物的平行自扩散系数之间的各向异性行为。在孔的中心，与平行的相比，通过降低垂直自扩散系数的值来体现限制效应。混合物组成起着重要作用，因为较高的乙烷含量表明平行组分之间的各向异性更大。