Properties Research on Guar-Crosslinked Fracturing at Different pH Value

The alkaline borate crosslinking fracturing fluid has been widely used in the oilfield. But with the development of low-permeability reservoirs, it is more and more important to reduce the formation damage from fracturing fluid. The acid fracturing fluids for its good capacity of inhibit clay swelling and application in CO₂ energization system or foam system has aroused extensive concerns. This paper evaluates the performance of guar-crosslinked fracturing fluids in the alkaline or acid condition, including their temperature stability, shearing resistance, gel breaking capability, residue content, filtration property, viscoelastic property and clay swelling property. The results show that gel viscosity maintains about 50% at 170s^-1 continuous shearing for 120min under acid condition, but the viscosity can maintain about 70% under alkaline condition. The alkaline system has better shearing resistance property. As to the temperature stability, the acid fracturing is better for above 140℃ than the alkaline system for only about 120℃. The coefficient of static filtrate loss is below 6.0×10^-4m/min^1/2 to the acid system and is above 6.5×10^-4m/min^1/2 to the alkaline system. The acid system's residue content is below 350mg/L, while the alkaline system is about 400mg/L. The acid fracturing fluid has better performance of inhibit clay swelling and less formation damage, so it is more effective for deep, low-permeability fracturing well.