Experimental Investigation of Flowback Surfactants: Anionic vs Cationic vs Non-Ionic Surfactants

Abstract Hydraulic fracturing is a critical step in hydrocarbon production from low permeability reservoirs. Additionally, flowing the well back is one of the most important post-fracturing mechanisms that affects the well's long-term performance. Surfactants have been commonly used as flowback aids, where they accelerate the flowback of the well and increase hydrocarbon productivity. Through several experimental tests, this study compares the effectiveness of an anionic (AS), a cationic (CS) and three non-ionic surfactants (NS1, NS2 and NS3) as flowback aids. Five surfactants were tested in this study. First, a tensiometer was used to measure each surfactant's surface tension in air and interfacial tension (IFT) with decane (oil phase) using the pendant drop method. Secondly, using the sessile drop method, the tensiometer was used to measure the contact angle of a de-ionized (DI) water droplet on a surfactant-wet glass slide to evaluate changes in surface wettability. Finally, sand column tests were performed, wherein fracturing fluids comprising a friction reducer (FR) and each of the surfactants were introduced into sand packs and the flow rates of the fracturing fluid and diesel through the pack were measured at ambient conditions. The five surfactants showed comparable surface tension values ranging from 30 to 34 dynes/cm. As for their interfacial tension with decane, the five surfactants ranked from the lowest IFT to the highest IFT as follows: NS1 < AS < NS3 < CS < NS2. As for the contact angle measurements, the DI water droplet had the lowest measurement with 1.0 gal-per-thousand-gal (gpt) AS, and the highest measurement with 1.0 gpt CS. Furthermore, AS and NS3 showed the best flowback performance in the sand column, while CS did not enhance the flowback at all. NS1 and NS2 also showed some flowback improvement in the sand column test but not as pronounced as with AS and NS3. The results suggest that the surface tension measurements did not display a correlation with the flowback results in the sand column. Additionally, the interfacial tension measurements did not show a clear correlation to the flowback in sand either. On the other hand, the results suggest that enhanced flowback in the sand column was correlated with a reduced contact angle of the DI water droplet on the glass slide wetted by fracturing fluid with surfactant relative to fracturing fluid without surfactant. This study shows that the anionic surfactant and one of the three non-ionic surfactants were the best performers in the sand column as a flowback aid at ambient temperature and atmospheric conditions. It was shown that the contact angle of DI water on a glass slide correlated better than the surface and interfacial tension reduction displayed by the surfactants with flow of fracturing fluid and diesel through the sand pack.