Asphaltene deposition causes serious problems in the oil industry. Variation of oil composition and reservoir pressure is reported to be the most important factors that influence asphaltene deposition from reservoir oil. In this study, a mathematical model was developed to simulate asphaltene deposition during primary depletion and CO2 injection. The main purpose of this study is to investigate and to compare asphaltene deposition mechanisms due to primary depletion and CO2 injection. The solid model as thermodynamic model was applied to investigate asphaltene precipitation. A numerical model was established to the governing equations both in space and time and model parameters were determined by history matching. Because of the implicit and coupling nature of equations in the model, an iterative method was applied to solve the numerical equations. Results show that surface deposition, entrainment and pore throat plugging have occurred during primary depletion and CO2 injection. Deposit re-entrainment and surface deposition proceed against each other. So, in most situations one of these two mechanisms is dominant, and the other one might be ignored. Enhanced re-entrainment deposition allows flocculated asphaltene to change into precipitated asphaltene, or be dispersed into the oil phase. Also, surface deposition rate during CO2 injection is more important than due to primary depletion. Result shows that entrainment of asphaltene deposit and pore throat plugging are predominant mechanisms of physical deposition in CO2 injection. A thermodynamic modeling show that because of CO2 is a precipitant, asphaltene precipitation is more important during CO2 injection than primary depletion.

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