Study on reason analysis and removal solution on water locking damage in tight sandstone reservoirs

Abstract

Water Locking Damage, caused by hydraulic fracturing, is one of the main reasons for stimulation failure in tight sandstone gas reservoirs. How to minimize the external fluid retention is the key to solve this problem. Based on comprehensive analysis of formation liquid retention in core matrix and fracture, novel ethers surface active nano agent was used to effectively reduce the two key factors associated with capillary force firstly, then wetting reversal experiment, spontaneous imbibition test and core flood experiment were adopted to evaluate the effect of removing water locking damage, the liquid phase distribution in the brine-saturated core after gas driving before and after chemical treatment was analyzed by Computed Tomography scanner . The gas permeability and drainage efficiency of each stage in the core flooding experiment were tested, the improvement of gas permeability and drainage effect after treatment were calculated, which is used to verify the effectiveness of gas wetting nano-agent in removing water locking damage in tight sandstone gas reservoirs. Results show that the decrease of gas-liquid capillary force can effectively reduce the rate and amount of spontaneous permeability of core; The liquid-phase fluidity of fracture-free matrix cores treated with chemical agents increased by 1.72 times, and that of fracture-type cores by 2.13 times; images showed that after treatment the liquid phase distribution in the core was further reduced and mainly distributed in small pores. The potential for improving gas permeability and drainage efficiency of fractured core after treatment was higher than that of matrix core without fractures.