Development of Guar Gum Fracturing Fluid With Temperature Resistance of 150°C and Specific Gravity of 1.0~1.2g/m3

Abstract For major high temperature and deep reservoir in West China, hydraulic stimulation confronts challenges of true vertical depth more than 6000 m and bottom hole temperature beyond 150°C. The long injection path from surface to stimulated formation induces significant friction. It commonly leads to very high ground pressure, which will exceed the limit of ground pumping equipment. In addition, conventional fracture fluid systems lost their fracturing ability and sand carrying capacity under high temperature. Therefore, it is urgent to develop a novel fracture fluid system with adjustable specific gravity and high temperature resistance for high temperature deep reservoir fracturing. In this article, the basic properties of guar gum were determined at first, and a high temperature and salt resistant organic boron crosslinking agent was synthesized. The optimal dosage and the optimal crosslinking pH, and the delayed time for crosslinking was studied. Then, the relationship between fluid density and weighting agent dosage is measured, which will facilitate the fracturing fluid density adjustment in the field. Three specific gravity formulas of fracturing fluid, that is 1.10, 1.15 and 1.20g/cm3, is optimized. Finally, the performance of fracturing fluid was evaluated comprehensively, and its gel-breaking and formation damage performance were tested. The apparent viscosity of 0.5wt% guar gum solution was 57.2mPa · s at room temperature (25 °C), and 29.1mPa · s at 150 °C. The synthesized high-temperature boron crosslinking agent YP-4 is colorless, transparent, and miscible with water. The optimal crosslinking concentration is 0.65wt%. The crosslinking occurred in the range of pH = 9∼12. The crosslinking time can be controlled within 3∼10min by adjusting the dosage and pH value. NaCl weighting fluid formulas with a density of 1.0∼1.2g/cm3 was optimized. The optimal fracturing fluid formulation was 0%∼26.4wt% NaCl brine +0.5wt% hydroxypropyl guar gum +0.3wt% alkaline pH regulator +0.65wt% crosslinking agent YP-4. This fracturing fluid can stable for more than 60min at 150 °C and 170s−1, and the final viscosity was high than 100 mPa·s. If the guar gum concentration was increased to 0.55wt%, the viscosity would exceed 260 mPa·s. 0.2wt% amine persulfate can be used to break the fracturing fluid, and the viscosity after breaking is less than 4mPa·s. What’s more, the fracturing fluid has good compatibility with various additives, and no flocculation or precipitation occurs within 24h. The average damage of gel breaking liquid to the core is 24.81%, which is relatively small. High temperature resistance and adjustable weight density have great advantages in field applications. Equipment constraints can be met while fracturing can be performed at minimal cost. This fluid system will provide beneficial support for high temperature and deep well fracturing.