Large amounts of aqueous based fluid are used in hydraulic fracturing of tight formations to enhance gas production. The pumped aqueous-based fluid is not fully recovered during flowback of well after the treatment resulting in increased water saturation, water blockage, clay swelling, reduced relative permeability, and long-lasting formation damage that impedes gas production. To enhance flowback fluid recovery and mitigate some of these problems, flowback aids are developed for tight sandstone and carbonate gas reservoirs.<br/>This paper describes four different nano emulsion based flowback aids specifically developed for gas bearing sandstone and carbonate formations. The flowback aids were developed from a blend of various ester-based solvents, alcohols and surfactants to form optically clear nano-emulsions. The flowback aids were characterized by determining their surface and interfacial tension in fracturing fluid. The performance of fluids was evaluated by fracturing fluid displacement tests in packed sand and carbonate columns using flowing gas. Core flow tests were performed with sandstone and carbonate cores (1-15 mD) at 300°F to determine the regained permeability in presence of flowback aids in fracturing fluid using gas. <br/>All of the developed flowback nano-emulsions demonstrated low surface tension and interfacial tension (22-30 mN/m) in fracturing fluid. The particle size of the nano-emulsions was found to be around 5-15 nm. It has been found that nano-emulsions formulated using non-ionic surfactants worked better at fluid displacement by gas in sandstone packed columns, whereas mixtures of cationic and amphoteric-based surfactants worked better for carbonate packed columns. These formulations not only provide quick aqueous fluid displacement by gas but also greatly enhance the rate of gas flow. In core flow experiments conducted with broken slickwater fluids and broken zirconium crosslinked fluid, it was determined that in the absence of flowback aid the regained permeability was around 50%, whereas with flowback aids added it was increased to 60-75%. Some of the flowback aids developed for oil bearing formations in sandstone and carbonate were not effective for the gas medium.

Nano emulsions for enhanced fluid flowback recovery from tight sandstone and carbonate gas reservoirs

ACS Spring Meeting 2021

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