In toluene, asphaltenes are dispersed as molecules at low concentrations, as nanoaggregates at moderate concentrations, and as clusters of nanoaggregates at high concentrations. These three asphaltene species are codified in the Yen–Mullins model. For reservoir crude oils, equilibrated asphaltene gradients can be modeled with the Flory–Huggins–Zuo equation of state (EoS). The gravity term and other terms depend on the particle sizes of the asphaltenes which are given in the Yen–Mullins model; these different asphaltene species (molecular and two nanocolloidal species) have been identified in gravity gradients in various reservoir studies. Here, the asphaltene gradient in a large reservoir is examined and found to be consistent with a molecular dispersion of asphaltenes in the crude oil. A variety of fluid and reservoir properties are evaluated to ensure validity of the analysis, particularly of thermodynamic equilibrium of the reservoir fluid. For crude oil samples throughout the reservoir, downhole fluid analysis (DFA), gas chromatography (GC), and two-dimensional gas chromatography (GC×GC) with cubic EoS and geochemical interpretation are consistent with fluid equilibration. Pressure measurement and production results are also consistent with fluid equilibration. This analysis is applicable to other reservoirs; molecular dispersions of asphaltenes are expected for other light oil reservoirs.

中文翻译：

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轻质油藏中沥青质分子的重力梯度

在甲苯中，沥青质以低浓度的分子，中等浓度的纳米聚集体和高浓度的纳米聚集体的形式分散。这三种沥青质物种在Yen-Mullins模型中进行了编码。对于储层原油，可以使用Flory-Huggins-Zuo状态方程（EoS）对平衡的沥青质梯度进行建模。重力项和其他项取决于Yen-Mullins模型中给出的沥青质的粒径；在各种储层研究中，已经在重力梯度中确定了这些不同的沥青质物种（分子和两个纳米胶体物种）。在这里，检查了一个大型油藏中的沥青质梯度，发现与沥青质在原油中的分子分散相一致。评估了各种流体和储层特性，以确保分析的有效性，尤其是储层流体热力学平衡的有效性。对于整个油藏中的原油样品，井下流体分析（DFA），气相色谱（GC）和具有立方EoS和地球化学解释的二维气相色谱（GC×GC）与流体平衡相一致。压力测量和生产结果也与流体平衡相一致。该分析适用于其他油藏。沥青质的分子分散体有望用于其他轻质油藏。二维气相色谱法（GC×GC）与立方EoS结合地球化学解释与流体平衡相吻合。压力测量和生产结果也与流体平衡相一致。该分析适用于其他油藏。沥青质的分子分散体有望用于其他轻质油藏。二维气相色谱法（GC×GC）与立方EoS结合地球化学解释与流体平衡相吻合。压力测量和生产结果也与流体平衡相一致。该分析适用于其他油藏。沥青质的分子分散体有望用于其他轻质油藏。