Viscoelastic Evaluation of a Surfactant Gel for Hydraulic Fracturing

Abstract

Abstract A new viscoelastic surfactant-based fluid was developed as an alternative to conventional fracturing fluids. The surfactant gel structure can be formed by adding a combination of cationic and anionic surfactants to water. This technology enables a clean fluid that can be prepared in fresh water, brines, or even produced waters without requiring biocides. Also, the cationic surfactant in the system functions as a temporary clay control agent or KCl replacement. The objective of this study is to evaluate the proppant suspension ability of the system, and its dependence on total surfactant concentration (TSC), cationic/anionic surfactant ratio (C/A), and temperature. Elastic and viscous properties (G’ and G") of twelve different formulae were measured using an oscillatory rheometer. Static and dynamic proppant settling tests were conducted at 2- to 4-ppg concentrations. Three proppant types were selected that had the same size, but different densities and shapes. Based on the experimental results obtained, the apparent viscosity of the surfactant gel was found to be a strong function of the TSC and temperature, while it has a weak dependence on C/A ratio. The viscous regime increased with increasing temperature and increasing TSC, while the elastic regime increased only with increasing C/A ratio. C/A ratio was found to be the primary parameter that affects proppant suspension. Only the formulae that had C/A ratio higher than 1.5 and TSC greater than 30 gpt displayed good proppant suspension properties. For these systems, proppant shape didn't affect the settling velocity. The viscous regime region was not affected by increasing the breaker concentration, but the values of G’ and G" decreased with increasing breaker concentration. Viscosity reduction profile was affected greatly by temperature and TSC, but C/A ratio did not have any significant effect. Results obtained can be used to better design hydraulic fracturing treatments.