Asphaltene deposition during natural depletion and miscible gas injection is a common problem in matrix and near well-bore region of oil reservoir throughout the world. This problem may lead to formation damage and reduction in production. Understanding the permeability reduction mechanisms during different processes of production is vital in optimizing production and injection processes in order to minimize the formation damage.

In this study, asphaltene deposition during natural depletion and miscible CO2 injection was conducted through core flooding tests at reservoir conditions. The natural depletion was done at several pressure steps while CO2 injection was performed simultaneously with live oil into the core sample. The CO2 mole percent in injected fluid was chosen to be more than the onset value. According to static experiments the onset of asphaltene precipitation due to CO2 injection was equal to 10% mole percent for the desired oil.

The main purpose of this paper is to consider asphaltene deposition mechanisms including surface deposition, plugging and filtration cake formation during primary depletion and CO2 injection. Consequently these mechanisms were investigated using related models. Based on results, plugging became dominant mechanism of permeability impairment, although surface deposition may exist during the tests. The pressure drop diagrams confirm the most pressure reduction was encountered at the entrance of the core; hence permeability reduction at initial part was more severethan the final portion. The results of this work may be helpful for understanding of permeability reduction mechanisms related to asphaltene deposition during natural depletion and CO2 injection in this heavy oil reservoir.

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