Research and Application of the Low Concentration Viscosity-Variable Slickwater Fracturing Fluid System

Given the requirements of large-scale multi-stage fracturing (stimulated reservoir volume-oriented) in horizontal wells, the research and development of the viscosity-variable slickwater fracturing fluid system are carried out to solve the application problems of low solid content (20%–30%), high required concentrations, slow dissolution, poor thickening performance, and proneness to stratification of the previously extensively-used slickwater. The molecular structure design is performed to enable instant dissolving, viscosity increasing, and drag reducing. The core material of multi-component polymers is synthesized by introducing the rigid functional monomer and high-polarity hydrophilic monomer into the molecular chain structure, based on which the suspension-type drag reducer is developed. The resultant low concentration viscosity-variable slickwater fracturing fluid system delivers excellent performance featuring instant dissolution, low use concentrations, low friction, and viscosity-variability. The experiment results show that the aggregates of the low concentration viscosity-variable slickwater are dispersed when the drag reducer concentration is low—the viscosity is 2.74 mPa·s at the concentration of 0.05%. Moreover, the aggregates are combined into a spatial network structure, when the drag reducer concentration is high—the viscosity is 18.56 mPa·s at the concentration of 0.3%. With this feature, the presented slickwater can be converted between slickwater and proppant-carrying fluids. Meanwhile, the drag reduction rate of the low viscosity slickwater is high, 79.46% for the low-viscosity slickwater and 70.01% for the high viscosity slickwater. The drag reduction performance is good. The field test results state that the system presents the advantages of the low required concentration, high drag reduction rate, excellent proppant carrying performance, and rapid dissolution. It enables injection without in-advance mixing and thus eliminates the need for the continuous mixing device. Manpower and materials are saved and operation costs are reduced.