If matrix is water wet and enough amount of water is supplied in fractures, capillary imbibition becomes the governing recovery mechanism in naturally fractured reservoirs. When the matrix contains heavy oil, however, this process becomes highly ineffective due to slow recovery rate and high residual oil saturation. Additional methods, other than waterflooding, such as injection of surfactant solution, polymer solution or hot water should be considered to increase the effectiveness of the capillary imbibition recovery of heavy matrix oil.

This paper includes the results and analysis of the laboratory scale experimentation of these three methods. Experiments are conducted on Berea Sandstones (water-wet sample) using heavy oil samples with the viscosities ranging between 185 and 630 cP. Carbonate cores (oil-wet limestone samples) were also used with light oil samples for comparison purpose. Different boundary conditions are created using epoxy coating. Based on boundary conditions, co- or counter-current type capillary imbibition takes place. Performances of the three methods are compared in terms of ultimate recovery and recovery rate. It is observed that all three methods yield higher and faster capillary imbibition recovery compared to waterflooding. The contribution of chemical additives and high temperature of water becomes more pronounced as the viscosity of oil increases. This contribution is more prominent on ultimate recovery than the recovery rate, especially for chemical solution cases.

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