A salt-induced smart and tough clean hydrofracturing fluid with superior high-temperature and high-salinity resistance

Hydraulic fracturing is an important technology to improve oil and gas productivity for reservoirs of both conventional and unconventional. To minimize reservoir damage during hydraulic fracturing, researchers have aimed to develop clean fracturing fluids based on viscoelastic surfactants (VESs); however, reduced efficiency at high temperature and high salinity limits their wider applications. Here, an ultra-long-chain cationic surfactant docosyl(trimethyl)azanium chloride (DCTAC) was proposed to prepare fracturing fluid in the presence of high content of various inorganic salts to address this problem. DCTAC shows excellent salt tolerance, forming a homogeneous solution in 22 % NaCl or 55 % CaCl2 at 60 degrees C, which is several times higher than that for previously reported VESs. Salt can induce DCTAC to form an entangled three-dimensional wormlike micelles network, imparting the bulk fluid excellent rheological properties. DCTAC-thickened fluids show good sand carrying and gel-breaking performance, and they can resist a temperature of up to 140 degrees C and a salinity level of at least 16 x 104 mg ?L-1. Compared with previously reported clean fracturing fluids, DCTAC-thickened fluid shows superior high-temperature and high-salinity resistance. The mechanism is elaborated and discussed. The findings in this study are helpful to understand surfactant aggregates stability and assist the development of novel stable supramolecular nanostructures.