Experimental study of some important factors on nonwetting phase recovery by cocurrent spontaneous imbibition

• Factors affecting cocurrent spontaneous imbibition were studied experimentally.
• Both one- and multi-dimensional experiments were performed.
• Linear relationship exists between recovery and square root of time.

Spontaneous imbibition, defined as the displacement of nonwetting phase by wetting phase in porous media by action of capillary forces, is important in many applications within earth sciences and in particular in naturally fractured oil and gas reservoirs. Hence, it is critical to investigate the various aspects of this process to correctly model the fractured reservoir behavior. In this study, twenty four experiments were conducted to study the effect of rock properties, lithology of porous medium, brine viscosity and boundary conditions on displacement rate and final recovery by cocurrent spontaneous imbibition (COCSI) in brine-oil systems. The results can be extended to brine-gas systems, as well. The porous media were reservoir sandstone and limestone samples from Iran. Brines with different viscosities (1, 3.3, 7 and 18 cp) were used as the wetting fluids whereas kerosene and liquid paraffin with viscosities of 1.13 and 28 cp were the nonwetting fluids. Two boundary conditions were simulated; one-dimensional COCSI where the lateral surfaces of vertically positioned core samples were sealed and brine and oil were covering, respectively bottom and top surfaces of the cores; and multi-dimensional COCSI where the lower and upper halves of core samples were in contact with, respectively brine and oil. The presented experiments provide a data base to verify the future analytical and numerical models. The obtained data was further used to check the hypothesis of linear relationship between the recovery by COCSI and square root of time in the systems where both displacing and displaced fluids were viscous. The viscosity ratio, defined as the ratio of brine viscosity to oil viscosity, ranged from 0.04 to 15.93.