LAUSR

Abstract Capillary and gravity forces are the controlling mechanisms in fractured reservoirs recovery. Most of the fractured reservoirs are carbonate formations with mixed wet and oil wet rocks. One of the techniques to improve the oil recovery from these reservoirs is surfactant treatment in the water invaded zone of carbonate fractured formation known as surfactant-aided gravity drainage. A number of experimental and modeling studies are available in this research area however, a modeling approach validated with the experimental data to consider different conditions in the reservoir, including rock physics, fluid properties, water salinity and surfactant functionalities is still a necessary element before the pilot tests for this recovery technique. In this work, a modeling approach is proposed to provide insight into the engineering aspects of this process. It defines a reservoir rock matrix (core scale) surrounded by the surfactant-brine solution in the fracture that acts as a boundary for the matrix in an imbibition test scenario. The reservoir rock is oil wet, therefore at first, the diffusive forces drive the solution into the matrix leading to wettability alteration. Afterwards the counter-current imbibition takes place in the early through the middle time of the experiment. Finally, the gravity drainage controls the recovery process. The parametric analysis investigates the effects of various parameters. Different modifications to the base case (validated with the experimental data) are performed for each parameter and then the resultant recovery curves are compared with the base case recovery. The parametric study shows that fluid densities, height, anisotropy ratio, permeability, connate water saturation, capillary pressure and the saturation end-points, are the main parameters influencing the performance of surfactant-aided gravity drainage. This study highlights the process sensitivity to the changes of the main effective displacement process parameters.