沥青质在高岭石表面吸附性的多尺度分子模拟研究

Asphaltene is a constituent of crude oil, prone to be adsorbed on the clay mineral surface in a reservoir. After adsorption of asphaltene the surface becomes hydrophobic, as a result, alkane which is the principle component of crude oil can be adsorbed. So asphaltene adsorption is unfavorable for oil recovery. Due to leakage of crude oil, asphaltene adsorption on soil clay mineral surface causes environmental damage. Previous studies show kaolinite exhibits the largest adsorption capacity of asphaltene among clay minerals. However, the adsorption mechanism is not clear. We plan to study asphaltene adsorption on kaolinite surfaces with multiscale molecular simulations: Firstly, first principle methods are used to compare influences of different functional groups on asphaltene adsorption; secondly, after building an asphaltene molecule model, classical all-atom molecular simulations are used to study its adsorption on kaolinite surfaces; thirdly, through fitting coarse-grained force fields with previous results, the aggregation of adsorbed asphaltene molecules is studied; in the end, the influences of salt on asphaltene adsorption and surface wettability are investigated. Through this study, the influences of functional groups, molecular structure and aggregation on asphaltene adsorption on kaolinite surfaces will be revealed. It is expected the results of our study will help enhancing oil recovery and controlling crude oil damage on environment.

沥青质是原油的组分，易吸附于储层粘土矿物表面而使其呈亲油性，促进作为原油主要组分的烷烃吸附在该表面，因而不利于石油开采。由于原油泄漏，沥青质吸附于土壤粘土矿物表面会造成环境污染。已有研究表明粘土矿物中高岭石对沥青质的吸附量最大，但吸附机理还不够清楚。申请者拟以多尺度分子模拟手段探究沥青质在高岭石表面的吸附机理：首先，使用第一性原理方法比较沥青质分子的不同类型官能团在表面的吸附性强弱；其次，构建一个沥青质分子的模型，以经典全原子分子动力学方法模拟该分子在高岭石表面的吸附结构；再次，以前面的研究结果为参考拟合粗粒化力场，研究多个沥青质分子在表面的吸附聚集结构；最后，以粗粒化方法探究盐对沥青质吸附和高岭石表面润湿性的影响。本研究预计可全方位揭示沥青质的官能团、构型和聚集体对其在高岭石表面吸附的影响。项目成果预计可以为石油开采、原油污染治理提供理论知识指导。

极性有机分子（如沥青质）易吸附于石油储层的黏土矿物表面而使其呈亲油性，促进作为原油主要组分的烷烃吸附于该表面，不利于石油开采。另一方面，原油泄漏造成的环境污染也与极性有机分子吸附于土壤黏土矿物表面相关。本研究以多尺度分子模拟方法研究有机分子（沥青质）在以高岭石为代表的黏土矿物表面的吸附机制，并揭示黏土矿物表面的水/油亲润性机理。此研究以第一性原理计算、经典分子动力学模拟和粗粒化分子动力学模拟等方法开展。第一性原理计算揭示了天然大有机分子（沥青质）的特征官能团在高岭石表面的吸附结构与相对吸附稳定性顺序。经典全原子分子动力学模拟方法揭示了有机分子在高岭石表面的吸附团簇结构与表面亲润性的相关关系。继而结合经典分子动力学与表面波分析方法探讨了高岭石表面的水亲润性与表面结构的关系。通过比较几种常见的盐离子力场，确立了使用经典分子模拟研究盐离子对有机质在黏土矿物表面吸附影响的方法。完成了对粗粒化分子力场的初步探索，揭示了疏水有机分子/极性分子/水的组合产生的液相分异行为。此研究可望对石油开采与原油污染治理等领域提供理论指导。