A dual-porous and dual-permeable media model for imbibition in tight sandstone reservoirs

Tight sandstone is an important oil reservoir in China which development is required water flooding. During water flooding treatments, imbibition is proven to strongly affect oil displacement. In this paper, capillary pressure is found not to be the only driving force to control imbibition in tight sandstone rock. Imbibition index is defined to be the second driving force. An experiment was designed to prove the imbibition index when water contacted tight sandstone samples. Then, a dual-porosity and dual-permeability numerical model was developed to simulate imbibition effect during water flooding in tight sandstone formations. Experimental results indicated that imbibition caused the weight of samples increased first and then declined. Increase is controlled by capillary force, and decline is affected by imbibition index. In Changqing formation in China, the imbibition index is 0.17-0.24, and the average imbibition index is 0.21.