Exploration of Factors Influencing Powdered Friction Reducer Hydration

Powdered friction reducers are gaining popularity in hydraulic fracturing applications whether delivered to stimulation sites as a powder or a slurry. Routinely bench tests are conducted to select the friction reducer based on hydration kinetics and viscosity build in the intended fracturing fluid. Waring blender tests typically have variables of mixing rpm, mixing duration and friction reducer loading. The viscosity build is measured at a specified shear rate on a specified rheometer. An experimental design which had variables of mixing rpm, mixing duration and various particle sized cuts of one unique powdered friction reducer was conducted. Other variables held constant were brine type, temperature, powder type, powder delivery method and blender volume. The responses of viscosity build over a 10-minute period every minute at 511s-1 were measured. The greatest influences on the build of viscosity were particle size and mixing duration. With the increasing use of powdered friction reducers, a better understanding of how they behave in laboratory testing needs to be methodologically and quantitatively studied. Inverse emulsion polymers have undergone such studies and resultant viscosity variability can be assigned to many factors. Powdered friction reducers have marketed values which claim superiority with respect to minimal impacts of fracturing fluid temperature and composition. Additionally, they may be more robust to cold and hot extremes for product storage, as well as a minimal number of additives such as surfactants and oils which may complicate formation interaction and flowback. A common anionic friction reducer was sorted and classified by particle size in 4 groups. This friction reducer was added to a Waring blender in a consistent manor to a 2.0 wt% KCl brine fracturing fluid at 10.0 pounds per thousand gallons. The experimental design had variables of mixing rpm (1,000 to 2,500) and mixing duration (10s to 70s), and particle size average (111μ to 232μ). The response of viscosity measured every minute for 10 minutes at a shear rate of 511s-1 with an Anton Paar MCR-302e with a double gap configuration. The ADJ-R2 ranged from 0.98 to 0.99 depending on the specific minute response. Since model fit well time was added as a variable and ADJ-R2 was 0.98. In general, smaller particles hydrate faster to provide higher viscosities at lower mix duration, but the viscosity declines as mixing time increases, whereas larger particles increase the fluid viscosity at a slower rate, but the viscosity decline is less dependent on mixing duration. These results are expected, but now have been studied in a quantitative, multivariate sense. This indicates that a specific customer may place a demand on a specific test where the best product is highly dependent on the testing method and by no way universal in acceptance. The resultant friction reduction in 2wt% KCl indicated particle size had a minimal influence on performance. When running bench tests with the intention of matching field hydration of powders whether dry added or delivered in slurry form, it is vital to understand the hydration viscosity variances that are attributed to the method and specific product used. Many studies on the viscosity builds of inverse emulsion friction reducers indicated the test method and product type influences the results. This recent study indicates viscosity build and inferred friction reduction depends on the specific method and the specific nature of powdered friction reducers. Therefore, caution must be placed on any powder hydration test run at a single speed, mixing duration and powder loading.