Oil recovery by counter-current spontaneous imbibition: Effects of matrix shape factor, gravity, IFT, oil viscosity, wettability, and rock type

The effects of the matrix shape factor, wettability, gravity, rock type, oil viscosity, and interfacial tension on the rate of capillary imbibition and development of residual non-wetting phase saturation were studied experimentally in this paper. Experiments were conducted on Berea sandstone and Indiana limestone samples. Cylindrical samples with different shape factors were obtained by cutting the plugs 1/2, 1 and 2 in. in diameter and 2, 4, and 6 in, in length. All sides were coated with epoxy except one end to ensure counter-current interaction. Static imbibition experiments were conducted on vertically and laterally situated samples to incorporate the effect of gravity where the imbibition took place upward and lateral directions, respectively. Brine-kerosene, brine-mineral oil and surfactant solution-mineral oil pairs were used as fluids. The rate of imbibition was evaluated for different matrix size, shape factor, wetting/non-wetting phase types and IFT. Conditions at which the shape factor controls the residual oil development were identified. It was observed that the residual oil after capillary imbibition is influenced by the matrix shape factor for the vertically positioned samples (unlike horizontal samples). In the low IFT experiments, surfactant was found to play a strong role on the rate of imbibition and the development of residual oil saturation. Scaling analyses were performed testing and comparing four different scaling groups. The equations were modified to take wettability and gravity effects into account. A new empirically correlated-gravity sensitive characteristic length was introduced. (C) 2007 Elsevier B.V. All rights reserved.