Performance Evaluation of the Multifunctional Variable-Viscosity Slick Water for Fracturing in Unconventional Reservoirs

The traditional guar gum fracturing fluid system has the drawbacks of the fracturing process of unconventional oil and gas deposits, such as high drag resistance and large residuum harm, which is gradually replaced by the system of the slick water fracturing fluid. The conventional slick water system, however, still has the features of low sand-carrying capability. Therefore, high-viscosity slick water is often used in fracturing operations, but most of the high-viscosity slick water is difficult to prepare, dissolve, and break gels, which needs to be improved. Based on the abovementioned problems, a new type of multifunctional variable-viscosity slick water is proposed in this paper. The self-made loop drag test unit, a dynamic crack sand-carrying model, a multifunctional core flow device, and other equipment were used for testing, and a set of systematic evaluation methods for the performance of multifunctional variable-viscosity slick water are established. In addition, the mechanism of improving sand-carrying capacity and increasing viscosity and solubilization was explained through the macroevaluation experiment of polymer properties and the analysis of the polymer microstructure. The experimental results show that compared with high-viscosity slick water, the multifunctional variable-viscosity slick water has good drag-reducing performance, the drag-reducing rate can reach more than 75%; the intersection value of viscoelastic modulus is about 0.01 Hz, the sand carrying capacity is higher; the gel-breaking time is faster, the residue content is lower, 38.5 ppm; it has the characteristics of low harm, the harm rate to the core is 18.30%; and it also has the performance of enhancing oil recovery.