Study on pH-Responsive Delayed, Cross-Linking and Weighted Fracturing Fluid

Hydraulic fracturing of deep, high-temperature reservoirs poses challenges due to elevated temperatures and high fracture pressures. Conventional polymer fracturing fluid (QCL) has high viscosity upon adding cross-linking agents and significantly increases wellbore friction. This paper examines a polymer fracturing fluid with pH response and low friction. Experimental results indicate that cross-linking occurs quickly in acid, while alkali can slow the cross-linking process and reduce friction. Sodium carbonate (Na₂CO₃) serves as an effective candidate. An optimized formulation consisting of "salt + pH + polymer + cross-linking agent" is proposed in two stages: low viscosity for fracture generation and high viscosity for sand transport. PH control enhances polymer hydration, increasing sand-carrying in the low-viscosity stage. Scanning electron microscopy (SEM) reveals that the fluid's structure varies with pH, showing that alkali promotes a stable network structure. Infrared spectroscopy (IR) shows that higher pH increases negative charges of the polymer chains, which enhances their hydrodynamic radius, slightly raises viscosity, and enhances sand carrying. Field tests confirm the formulation's effectiveness, leading to lower operating pressures, stable sand transport, and notable production, averaging 107.57 m³ of oil and 276 m³ of gas per day. Overall, this research provides low-friction solutions for the efficient development of deep reservoirs.