Aggregation of asphaltenes followed by precipitation presents severe problems for existing technologies in the production, recovery, and processing of heavy oils. Better understanding of asphaltene behavior behind the processes of their precipitation and dissolution is vital to address this issue. While investigating the inhomogeneity of different oil systems, the reversibility of the asphaltene aggregation process initiated by flocculant in either asphaltene solution in toluene or crude heavy oil was revealed and investigated using magnetic resonance imaging methods. It was found that the inhomogeneous distribution of the flocculant initiates local spatial-selective asphaltene aggregation registered in a thin layer around the flocculant/oil sample interface. The local excess of flocculant concentration over the threshold of asphaltene precipitation onset is a driving force of this process. As the flocculant diffuses into the volume of the sample, a decrease of the asphaltene flocculated area is observed until it disappears when the equilibrium composition throughout the whole volume of the system is achieved. Depending on the overall flocculant concentration, the asphaltene aggregation may not be reversible and could be followed by subsequent precipitation of the asphaltene aggregates. The similarity of the phenomena observed for the model asphaltene solutions and crude heavy oil samples was established. Partial mechanical stirring of the multicomponent system comprising flocculant and oil or asphaltene solution does not prevent the formation of the local zones with increased concentration of asphaltene aggregates; those sizes evolve depending on the flocculant concentration. The results obtained in this work are consistent with the generally accepted concept of asphaltene precipitation reversibility depending on the system composition and are compatible with the observations obtained by other methods. The approach presented can provide deeper insight into the asphaltene precipitation reversibility issue and can facilitate the understanding of asphaltene behavior in heavy oils.

中文翻译：

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磁共振成像原位显示沥青质聚集的可逆性

沥青质的聚集随后沉淀对于重油的生产，回收和加工中的现有技术提出了严重的问题。更好地了解沥青质在其沉淀和溶解过程背后的行为对于解决该问题至关重要。在研究不同油体系的不均匀性时，揭示并通过磁共振成像方法研究了絮凝剂在甲苯或原油重油中的絮凝剂引发的沥青质聚集过程的可逆性。发现絮凝剂的不均匀分布引发了在絮凝剂/油样品界面周围的薄层中记录的局部空间选择性沥青质聚集。絮凝剂浓度超过沥青质沉淀开始阈值的局部过量是该过程的驱动力。当絮凝剂扩散到样品的体积中时，观察到沥青质絮凝面积的减少，直到达到整个系统整个体积的平衡组成时，沥青质絮凝面积消失为止。取决于总的絮凝剂浓度，沥青质聚集体可能是不可逆的，并可能随后沉淀沥青质聚集体。建立了模型沥青质溶液和原油重油样品中观察到的现象的相似性。包含絮凝剂和油或沥青质溶液的多组分系统的部分机械搅拌不会阻止随着沥青质聚集体浓度的增加而形成局部区域；这些尺寸根据絮凝剂浓度而变化。这项工作中获得的结果与公认的沥青质沉淀可逆性概念（取决于系统组成）相一致，并且与通过其他方法获得的观察结果兼容。提出的方法可以提供对沥青质沉淀可逆性问题的更深入了解，并可以促进对重油中沥青质行为的理解。这项工作中获得的结果与公认的沥青质沉淀可逆性概念（取决于系统组成）相一致，并且与通过其他方法获得的观察结果兼容。提出的方法可以提供对沥青质沉淀可逆性问题的更深入了解，并可以促进对重油中沥青质行为的理解。这项工作中获得的结果与公认的沥青质沉淀可逆性概念（取决于系统组成）相一致，并且与通过其他方法获得的观察结果兼容。提出的方法可以提供对沥青质沉淀可逆性问题的更深入了解，并可以促进对重油中沥青质行为的理解。