Methylimidazolium Ionic Liquids as Flowback Additives for Enhanced Hydraulic Fracturing

Abstract Unconventional reservoirs, such as shale gas and tight oil formations, present challenges due to their low permeability and complex rock compositions. Hydraulic fracturing is crucial for exploration, involving high-pressure injection of fracturing fluid to create fractures. However, this process encounters issues like water blockage and reduced permeability. Conventional flowback additives may lose effectiveness in such harsh conditions, leading to decreased recovery rates and operational challenges. This study aims to evaluate the performance and effectiveness of methylimidazolium ionic liquids as flowback additives in high-salinity and high-temperature conditions. A series of experimental analyses were conducted to evaluate the performance of methylimidazolium ionic liquids with varying ionic groups and chain lengths. Specifically, four different chain lengths of methylimidazolium tetrafluoroborate-based ionic liquids (referred to as ST1, ST2, ST3, and ST4) were screened with carbon chain lengths of 2, 4, 6, and 12, respectively. Finally, the performance of methylimidazolium tetrafluoroborate-based ionic liquids was compared to methylimidazolium chloride-based ionic liquids with similar carbon chain length: X1 (1-Butyl-3-methylimidazolium chloride), X2 (1-Hexyl-3-methylimidazolium chloride), and X3 (1-Decyl-3-methylimidazolium chloride). The screening methodology included measuring surface tension to estimate critical micelle concentrations, using a spinning drop tensiometer (SDT) to measure interfacial tension, and employing contact angle measurements to assess the impact of flowback additives on wettability and displacing behavior. All experiments were conducted using seawater with a salinity of 57,000 ppm as the base fracturing fluid, and temperatures up to 90°C. Surface tension measurements were conducted using seawater with a salinity of 57,000 ppm. The critical micelle concentration (CMC) values exhibited a noticeable decrease with the increasing carbon chain length of the tested ionic liquids. ST1, characterized by the shortest chain length, remained relatively constant between 50-52 mN/m. ST2 demonstrated stability within the range of 47-49 mN/m, while ST3 settled around 42-45 mN/m. ST4, with the longest chain length, exhibited the lowest CMC values and maintained a surface tension between 26-28 mN/m, with CMC values less than 1000 ppm, which is economically advantageous. Similar performance was observed in methylimidazolium chloride-based ionic liquid with a reduction in the surface tension with increasing the chain length. The overall performance of chloride-based ionic liquids was lower than tetrafluoroborate-based ionic with surface tension of 35 mN/m compared to 26 mN/m for the same carbon chain length of 1-Decyl-3-methylimidazolium IL. Moreover, the IFT measurements showed that ST4 reduced the IFT to 4 mN/m compared to 7 mN/m for X3, reflecting a better performance for the tetrafluoroborate-based IL compared to Chloride-based IL. Our findings suggest that ionic liquids, especially methylimidazolium tetrafluoroborate-based, offer a promising solution as eco-friendly flowback additives, especially in challenging environments with high temperatures and salinity, where traditional additives fall short. This development could pave the way for more sustainable practices in hydraulic fracturing, helping to alleviate water blockage, minimize formation damage, and improve shale gas extraction.