Preparation and laboratory study of a sodium carboxymethyl cellulose smart temperature‐controlled crosslinked gel fracturing fluid system

Abstract

Water‐based fracturing fluids are widely used in the development of tight, low‐permeability unconventional oil and gas fields, where the crosslinking agent component can thicken the low‐viscosity, high‐flowability base fluid to ensure sufficient proppant is transported from the wellbore to the tip of the fracture and generate the required net pressure to support the fracture. Zirconium crosslinking agents are widely used due to their good stability and high shear resistance. In the paper, glycerin, zirconium chloride, lactic acid, sodium hydroxide, and water were reacted at a molar ratio of 7:1:3:4:98 and a temperature of 80°C for 5 h; Using triethanolamine, zirconium chloride, lactic acid, and water as raw materials, the molar ratio of 4:1:3:98, reaction at 80°C for 5 h, and then zirconium lactate crosslinker and triethanolamine zirconium lactate crosslinker were synthesized respectively, which were incorporated into a newly designed self‐generating acid temperature‐controlled crosslinking system to crosslink salt‐resistant cleaning fracturing fluids mainly composed of sodium carboxymethyl cellulose, achieving delayed crosslinking of the fracturing fluid in different temperature formations. The strong crosslinking temperature range of glycerol‐lactic acid zirconium and the rheological properties of triethanolamine zirconium lactate gel and zirconium lactate gel in the system were tested. The viscosity of triethanolamine zirconium lactate gel and zirconium lactate gel were 88.86 and 94.69 mPa·s, respectively, at the shear rate of 300 s−1, and the viscosity remained above 200 mPa·s at the shear rate of 170 s−1, 60°C for 1 h. These figures far exceed the gels formed by commercially purchased zirconate. This system can make glycerol lactic achouid zirconium crosslinking agents undergo strong crosslinking at 40–65°C and triethanolamine lactic acid zirconium undergo strong crosslinking at 55–75°C. It has significant implications for the delayed crosslinking effect of massive fracturing operations.