分子动力学模拟方解石和白云石润湿性

Molecular Dynamics Simulation of Wettability of Calcite and Dolomite

利用分子动力学模拟研究油水分子在方解石和白云石表面的吸附,分析体系的平衡构型、相对浓度、径向分布函数和吸附能,研究方解石和白云石的亲水性并对比二者差异.根据油水分子吸附规律分析方解石/白云石-油水体系作用机理.研究表明:白云石-油水体系更易达到热力学稳定状态并且体系更加稳定;方解石和白云石表面均能够优先吸附水分子并在表面形成双层结构的水膜.其中,白云石表面对水分子吸附强度大于方解石;稳定吸附过程分为两步:范德华力、静电力和O(CaCO3, CaMg(CO3)2)-H(H2O)氢键共同影响下水分子向晶体表面移动并吸附形成紧密吸附层;O(H2O)-H(H2O)氢键作用下游离的H2O向晶体表面靠近形成扩散层.从分子尺度解释方解石/白云石亲水特性,为碳酸盐岩储层润湿性研究奠定理论基础.

We studied adsorption characteristics of oil-water system on calcite and dolomite surface with molecular dynamic simulation.To study wettability of calcite/dolomite surfaces,we analyzed equilibrium conformation,relative concentration,radial distribution function and adsorption energy of calcite/dolomite-oil/water system.Then,we proposed a two-step adsorption mechanism.It shows that dolomite-oil/water system is more easily to achieve thermodynamic stability and is more stable;A water film is formed on calcite and dolomite surfaces,which is a double-layer structure;There are interactions among oil molecules,water molecules and the crystal surface;Attraction of dolomite surface to oil and water molecules is stronger than calcite.Finally,we divided the adsorption process into two steps:Water molecules adsorbed on crystal surfaces form a tightly adsorbed layer under van der Waals forces,electrostatic forces and O(CaCO3,CaMg(CO3)2)-H(H2O)hydrogen bonds.In addition,the remaining water molecules move to the crystal surface form a diffusion layer under the influence of O(H2O)-H(H2O)hydrogen bonds.It reveals wettability formation and alteration mechanisms on calcite and dolomite surface,which paves a foundation of further enhance oil reovery.