Schlumberger Cambridge Research, High Cross, Madingley Road, Cambridge, CB3 0EL, United Kingdom.
Faraday Discuss. 2010;144:271-84; discussion 323-45, 467-81. doi: 10.1039/b902305b.
Asphaltenes are known as the 'cholesterol' of crude oil. They form nano-aggregates, precipitate, adhere to surfaces, block rock pores and may alter the wetting characteristics of mineral surfaces within the reservoir, hindering oil recovery efficiency. Despite a significant research effort, the structure, aggregation and deposition of asphaltenes under flowing conditions remain poorly understood. For this reason, we have investigated asphaltenes, their aggregation and their deposition in capillary flow using multi-scale simulations and experiments. At the colloid scale, we use a hybrid simulation approach: for the solvent, we used the stochastic rotation dynamics (also known as multi particle collision dynamics) simulation method, which provides both hydrodynamics and Brownian motion. This is coupled to a coarse-grained MD approach for the asphaltene colloids. The colloids interact through a screened Coulomb potential with varying well depth epsilon. We tune the flow rate to obtain Pe(flow) >> 1 (hydrodynamic interactions dominate) and Re << 1 (Stokes flow). Imposing a constant pressure drop over the capillary length, we observe that the transient solvent flow rate decreases with increasing well depth epsilon. The interactions between the mesoscopic asphaltene colloids can be related to atomistic MD simulations. Molecular structures for the atomistic calculations were obtained using the quantitative molecular representation approach. Using these structures, we calculate the potential of mean force (PMF) between pairs of asphaltene molecules in an explicit solvent. We obtain a reasonable fit using a -1/r2 attraction for the attractive tail of the PMF at intermediate distances. We speculate that this is due to the two-dimensional nature of the asphaltene molecules. Finally, we discuss how we can relate this interaction to the mesoscopic colloid aggregate interaction. We assume that the colloidal aggregates consist of nano-aggregates. Taking into account observed solvent entrainment effects, we deduct the presence of lubrication layers between the nano-aggregates, which leads to a significant screening of the direct asphaltene-asphaltene interactions.
沥青质被称为原油中的“胆固醇”。它们会形成纳米聚集体、沉淀、附着在表面上、堵塞岩石孔隙，并可能改变储层中矿物表面的润湿性特征，从而降低采油效率。尽管已经进行了大量的研究，但在流动条件下沥青质的结构、聚集和沉积仍未得到很好的理解。基于此，我们采用多尺度模拟和实验研究了在毛管流动中沥青质、其聚集和沉积。在胶体尺度上，我们使用混合模拟方法：对于溶剂，我们使用随机旋转动力学（也称为多粒子碰撞动力学）模拟方法，该方法既提供了流体动力学又提供了布朗运动。这与粗粒化 MD 方法相结合，用于模拟沥青质胶体。胶体之间通过带有变化势阱深度 ε 的屏蔽库仑势相互作用。我们调整流速以获得 Pe(flow) >> 1（流体动力学相互作用占主导地位）和 Re << 1（斯托克斯流）。在毛细长度上施加恒定压降，我们观察到随着势阱深度 ε 的增加，瞬态溶剂流速减小。中间距离处的平均力势 (PMF) 具有 -1/r2 吸引力，表明中等距离处的吸引力尾端存在吸引力。我们推测这是由于沥青质分子的二维性质。最后，我们讨论了如何将这种相互作用与介观胶体聚集体相互作用联系起来。我们假设胶体聚集体由纳米聚集体组成。考虑到观察到的溶剂夹带效应，我们推断出纳米聚集体之间存在润滑层，这导致了直接的沥青质-沥青质相互作用的显著屏蔽。
