Novel High Salinity and High Temperature Tolerant Surfactant-Based Fluids for Mitigation of Water Entrapment in Dry Gas Formations

Abstract

Abstract For hydraulic fracturing of low permeability dry gas formation, capillary discontinuity at the matrix-fracture interface and fluid entrapment in the hydraulic and natural fractures can impact the effective fracture half-length and thus result in loss of fracture conductivity. Adding surfactant-based novel fluids can reduce the capillary trapping of fluids by lowering the surface tension and modifying wettability to less water-wet condition and thereby improve the relative gas permeability and well productivity. In this work, a novel surfactant-based fluid was developed to be effective in reducing water entrapment. The surfactant formulation was evaluated in various reservoir conditions including Eagle Ford, Permian, Duvernay, Kansas St. Louis, and Bakken. The new formulation showed excellent stability under harsh reservoir conditions up to 150 °C and 27% TDS. Additionally, a laboratory workflow was developed to evaluate the efficiency of surfactant formulations in the mitigation of water entrapment using two-phase coreflood (CF). Our results show that three formulations (A, B and C) reduce the surface tension comparably. However, in the liquid recovery test using CF, formulations B and C outperformed A, resulting in much higher recovery of the aqueous fluid compared to the control case of formation brine. Wash-off tests were further performed by flushing the cores with fresh brine after treatment with novel formulations. The core treated with formulation C outperformed B after 5 pore volume (PV) flush of brine. Notably, for the core treated with formulation C, even after flushing with 140 PV of brine, the fluid recovery is still much higher compared to the brine case without treatment. Interestingly, formulation C performs even better in the harsh reservoir condition with high salinity brine, which can be explained by the three different adsorption patterns governing the interaction energy between surfactant and rock surface. This work demonstrates that tailoring fluid-rock interactions is crucial to reduce the water entrapment and thereby improve gas productivity for dry gas wells. Our workflow provides a comprehensive process to understand the mechanisms behind water entrapment and how to tailor novel formulations to reduce water entrapment in dry gas wells.