The Aggregation of Asphaltene Molecules as a Function of Carbon Dioxide Concentration
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Asphaltenes can present problems in production and flow assurance during tertiary enhanced oil recovery projects involving CO2 injection. Despite many years of research, asphaltene behavior remains poorly understood, and predictions of precipitation are unreliable. Even laboratory PVT studies often fail to predict problems in the field. The majority of the asphaltene theories focus on predicting asphaltene precipitation in a given reservoir fluid as a function of pressure and temperature. Recent credible research challenges the long held physical picture that asphaltenes are held in suspension in oil by resin micelles. Popular theoretical approaches are based on solubility theory, with most models including only two solubility parameters. Serious doubt has been cast on the application of the solubility models, and statistical mechanics theories such as SAFT (Self Associated Fluid Theory) have all been explored. This study investigates the problem from a new direction – the aggregate or floc size of asphaltene moieties as a function of CO2 concentration. The study looks at the distribution of the floc size as a function of CO2 concentration. Multiple experiments are done at various concentrations of CO2 in the same oil and differentially on each sample. Floc size groups are determined by sets of nano filter: 200 nm, 100 nm, 50 nm and 30 nm. The differential study provides a method of removing asphaltenes differentially from the same oil testing the resin hypothesis. The floc size feature discloses whether and at what size are flocs in dynamic equilibrium. Experimental results show that carbon dioxide injection produces asphaltene aggregation for all concentration of carbon dioxide. Floc size versus pore throat size is the most relevant parameter for predicting problems in the field.