Rheological experiments have been conducted with commercial and experimental friction reducers indicating certain profiles are advantageous for performance. In these profiles the factors of time and concentration are important in predicting the maximum performance window. These windows become apparent without the use of sophisticated rheological instrumentation.
The viscosity profile of a friction reducer is dependent on factors such as polymer charge, charge distribution, molecular weight, polymer concentration, solvent properties, specific shear rate and time. Often it is difficult to measure properties such as molecular weight and viscosity, both quite sensitive to the specific test method and many assumptions are made. In this study, the viscosity of the system depends on the shear history, concentration, and time of measurement. Most traditional viscosity methods assume a thermodynamic definition of polymer configuration. This assumption is valid for measurement of friction reduction after significant duration. However, in a hydraulic fracture, this time may not be realized during the volumetric transfer of the fluid from the pumps to the perforations. In a recirculating friction loop measurement, the friction reduction performance of an ideal candidate rapidly increases and then sometimes diminishes with recirculation time. A possible correspondence between this phenomenon can be linked to the measurement conducted in this study.
Shear rate sweeps were conducted on a variety of synthetic polymers with a Couette rheometer and a microchip rheometer. Variables studied were polymer type, concentration, shear history, time, solvent, make-down procedure, and atmosphere. Both inverse emulsion and dry friction reducers were studied. Friction reduction was measured on a once through system.
From this study, ideal friction reducer candidates can be selected by simply and rapidly examining the rheological profile and rheological nuances realized when conducting the measurements. When choosing an ideal friction reducer, it must perform rapidly and maintain the necessary friction reduction required for the time frame needed.