Treating Agent for Reducing Adsorption Damage of Slick Water on Coal Rock Surface

Abstract Hydraulic fracturing is generally required for coalbed methane to achieve economic production. Slickwater fracturing is one of the most commonly used technology. During fracturing, a million gallons of slickwater are pumped downhole to create fractures, and lots of fluid would filtrate into the formation matrix. The polymers in the fracturing fluid will be absorbed in the porous medium of coal rocks and then decrease the permeability of the reservoir. This paper studies the adsorption amount and the form of slickwater on the coal seam surface and proposes a method to relieve slickwater damage. First, we tested the damage of coal rocks caused by slickwater of different molecular weights. Then the adsorption capacity of different types of slickwater was measured through static adsorption experiments. The changes in adsorption morphology was analyzed according to the micro-morphology of the scanning electron microscope (SEM). Finally, the effect and mechanism of the adsorption release agent were discussed. The study shows that coal seam reservoirs block the gas-liquid percolation channels by forming a water film and polymer adhesion in the pore throat by adsorbing the slick water, resulting in a decrease in permeability and affecting subsequent drainage and gas recovery processes, thereby increasing the damage of slickwater to coal rock. After the improvement of the nano-emulsion NLR, the coal core injury removal rate reached 27.75%, the “gas-liquid-solid” static contact angle of the coal chips was reduced from 129° to 107°, and the surface hydrophilicity was weakened. Adsorption morphology changed from flat and smooth to a rough structure. NMR results prove that NLR reduces adsorption and retention.