Application of a New Modified HPG in Ultra-high Temperature Fracturing Fluid

To improve the thermal stability of thickening agent used in fracturing fluid, a new modified hydroxypropyl guar gum (HPG) thickening agent has been synthesized with hydroxypropyl guar gum, 2-pyrrolidone and (2-chloroethyl) trimethyl ammonium chloride. The ability of the thickening agent to resist high temperature was evaluated with TGA, and laboratory study was conducted on the conditions for the thickening agent to crosslink, as well as thermal stability, shearing resistance, gel breaking performance, residue content and core damage of the fracturing fluid formulated with the newly developed thickening agent. It was demonstrated that by introducing a rigid group into the molecular structure, the thermal degradation temperature of HPG was increased to 220℃, and the modified HPG had good thickening performance at a concentration of 0.6% in the fracturing fluid. The optimized formulation of the fracturing fluid is as follows:0.6% modified HPG + 0.5% high temperature swelling inhibitor BZGCY-C-FP + 0.5% high temperature clean-up additive BZGCY-C-ZP + 0.1% high temperature stabilizer BZGCY-Y-WD + 0.2% sodium carbonate + fresh water + organic boron-zirconium crosslinking agent (crosslinking ratio=100︰0.4). After sheared at 200℃ and 170 s^-1 for 120 min, the viscosity of the formulation was still higher than 60 mPa·s, indicating that the thermal stability of the fracturing fluid is improved. Field application showed that the new fracturing fluid has satisfied the needs for high temperature operation.