CO2 injection is one of efficient enhanced oil recovery (EOR) methods among gas flooding, however, asphaltene precipitation during CO2 injection might lead to production loss and reduced efficiency. To understand the mechanism of asphaltene deposition is necessary to develop effective engineering practice for minimizing the formation damage and to design the treatment program for restoring well productivity. The paper presents the development of the experimental apparatus for asphaltene precipitation during pressure decline and gas injection in addition to the results of asphaltene phase behavior and coreflood tests to identify the dominating factors associated with permeability reduction. Asphaltene phase behavior is studied to determine the relationship among pressure, temperature and asphaltene precipitation. Asphaltene onset pressure is measured by Solids Detection System (SDS). The pressure decline induces asphaltene deposition and the consistent result is obtained by the measurement of asphaltene content using SARA analysis. These results are used to estimate Asphaltene Deposition Envelope (ADE). ADE reveals the risk of asphaltene deposition when the pressure is decreased. It is a useful measure to predict flow problem in the reservoir and at the facilities due to asphaltene precipitation. The reversibility of asphaltene precipitation and re-dissolution is also investigated. Gas injection coreflood experiments are conducted on sandstone and carbonate cores to evaluate the asphaltene precipitation and its permeability reduction. Asphaltene is selectively deposited near the inlet of the core for CO2 injection, while asphaltene is equally distributed in the core for the hydrocarbon (associated) gas injection. Additional experiments confirm that the permeability is decreased with increase of asphaltene precipitation. The experimental investigation is necessary to further understanding of the asphaltene behavior in order to prevent asphaltene induced permeability reduction when the risk of asphaltene precipitation is expected due to gas injection and pressure decline.

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