Improved Oil Recovery in Asphaltic Reservoirs During Gas Injection

Abstract

Abstract A successful gas injection design is a challenging task in asphaltic reservoirs. Gas injection accelerates asphaltene deposition, which results in detrimental effects on field development and ultimate oil recovery. The main objective of this paper is to provide a workflow to mitigate asphaltene problems in reservoirs during gas injection. The workflow includes data gathering, fluid characterization, and dynamic asphaltene modeling using an in-house compositional reservoir simulator. The in-house simulator is capable of modeling (1) the effects of pressure, temperature, and composition variations simultaneously on asphaltene phase behavior, (2) asphaltene precipitation, flocculation, and deposition, and (3) wettability alteration due to asphaltene deposition. Three case studies were presented to investigate the effects of gas flooding, gas override, and wettability alteration on the dynamics of asphaltene precipitation, flocculation, and deposition. The simulation results showed that gas injection considerably increased the instability of asphaltene particles in the oil, and consequently, accelerated asphaltene precipitation and deposition in the reservoir. During miscible gas flooding, asphaltene mostly deposited at the front near the boundaries, where the front velocity was minimum. Moreover, asphaltene deposition occurred mainly in the bottom layer in the presence of gas override due to the lower velocity of the front in the bottom layer compared to the upper layer. Finally, the study revealed that wettability alteration due to asphaltene deposition had a major impact on the performance of the reservoir, specifically on the ultimate oil recovery, compared to the permeability reduction.