Experimental evaluations of nano high-viscosity friction reducers to improve acid fracturing efficiency in low-permeability carbonate reservoirs

A suitable pad fluid system creates a fracture surface with heterogeneous etching, reducing oil and gas flow resistance and improving the acid fracturing efficiency. The superior viscosity and friction reduction characteristics of a high-viscosity friction reducer have gradually replaced conventional slickwater and guar gum fracturing fluid. This study introduces nanoemulsions into a high-viscosity friction reducer, forming a nano high-viscosity friction reducer system resistant to acids and salts. Including nanoemulsions improves its viscosity, friction reduction rate, and imbibition oil recovery. Experimental results show that hydrophilic groups in nanoemulsions form hydrogen bonds with those in the high-viscosity friction reducer, increasing its viscosity by about 10% and enhancing its friction reduction performance by approximately 1.08 times under high flow rates. After breaking a gel, the nano high-viscosity friction reducer system has a core permeability damage rate of 19.66%, higher than conventional slickwater but significantly lower than guar gum breaking fluid. Under reacted acid conditions, an addition of nanoemulsions can transform oil-wet cores into water-wet ones, altering the direction of capillary forces and providing a driving force for imbibition oil recovery, with an imbibition recovery rate as high as 24.89%, 17.38% higher than a group without nanoemulsions. The ability of nanoemulsions to mobilize oil in both micro and macro pores indicates a substantial potential in utilizing fracturing fluid energy to displace oil for enhanced recovery. This study suggests that the nano high-viscosity friction reducers system can not only improve properties such as its viscosity and friction reduction rate, minimizing polymer invasion damage to a formation but also supplement formation energy and displace crude oil through imbibition, thereby achieving an integrated and efficient acid fracturing stimulation and enhanced oil recovery.