Experimental Investigation of Effective Parameters on Efficiency of Capillary Imbibition in Naturally Fractured Reservoirs

Abstract

When a matrix is saturated by a non-wetting phase, and the wetting phase fills the fracture network, capillary imbibition may occur. Capillary imbibition can be an effective recovery mechanism in water wet naturally fractured reservoirs (NFRs) where most of the oil is stored in tight matrix blocks. This paper presents the results and analysis of the laboratory experiments with variable parameters such as oil type, rock composition, temperature, permeability, porosity and fluid that invades the matrix. To investigate temperature effect on the efficiency of capillary imbibition mechanism, capillary imbibition tests were conducted under static conditions and at different temperatures, namely 22, 50 and 80 degrees C by using crude oils and carbonate samples taken from the same reservoirs. Also variable core sizes were used to study the block size effect on the oil recovery. The results of static imbibition experiments show that rock and oil properties are the dominant parameters in capillary imbibition. Furthermore, increasing the operational temperature also has a positive role in the process. Therefore, in thermal EOR methods, oil recovery increases due to the enhancement of the imbibition mechanism. Also the lighter oil show high sensitivity to capillary imbibition mechanism than the heavier one and using brine instead of pure water decreased the amount of oil recovery through capillary imbibition.