Enhanced regained permeability and fluid flowback from tight sandstone and carbonate oil reservoirs with unique flowback chemistry

Large amounts of aqueous-based fluids used in hydraulic fracturing of tight formations are not fully recovered immediately after treatment, resulting in increased water saturation, water blockage, clay swelling, reduced relative permeability, and long-lasting formation damage that impedes production. To enhance flowback fluid recovery, nano-emulsion based flowback aids were developed for oil-bearing sandstone and carbonate formations. The flowback aids were formulated using a blend of high-temperature stable ester-based solvents, alcohols, and surfactants to form optically clear nano-emulsions. All the developed flowback aids demonstrated low surface tension (22-30 mN/m) and interfacial tension (<6 mN/m), which is necessary for reducing capillary pressure. The particle size of the nano-emulsions was found to be 5-15 nm. The flowback aids were able to prevent the formation of the emulsion with crude oil. It has been found that nano-emulsions formulated using non-ionic and anionic surfactants worked better for sandstone, whereas non-ionic and cationic surfactant-based formulations worked better for carbonate. These formulations not only provide quick aqueous fluid displacement in column tests but also greatly enhance the rate of oil flow in core flow experiments conducted with broken slickwater fracturing fluids. It was determined that in the absence of a flowback aid, the regained permeability was around 40%, whereas with flowback aids it was increased to 65%-75%. The paper demonstrates the effectiveness of flowback enhancers to quickly recover the injected aqueous fracturing fluid, thereby reducing water saturation, which in turn enhances productivity, and shows the benefit of applying chemistry for low permeability oil reservoirs.