Increased interest in correlating rheological properties to the prediction of proppant transport and/or friction reduction performance produces sporadic and isolated experimental evidence. Obtaining accurate results specifically for viscosity, proposedly representative of proppant transport and friction reduction, is challenging and therefore, extrapolating polymer melt rheology to dilute polymer solutions is problematic particularly when applying linear viscoelastic theory. This paper presents a simultaneous, multivariable research approach illustrating how viscoelastic results and hypotheses for anionic, cationic, and amphoteric friction reducers in various brines provide insight into the limitations of constricted variable and experimental range methodology.
Establishing a relevant application window for viscoelastic friction reducers is complicated. Guar gum linear gels are viscous in nature and more approachable than synthetic friction reducers when manipulated for rheological experimentation and field application extrapolation. However, crosslinking of guar gum linear gels results in a viscoelastic fluid of greater complexity, thus even the simplest of linear gels must be subjected to a variety of unique bench tests differentiated by and specific to individual service companies’ field application requirements. Friction reducers’ crossover of storage and loss moduli are dependent upon how the reducers were dispersed and hydrated with respect to brine characters, times, and mixing energies. Furthermore, correlating rheological measurements developed for the melt state may not appropriately adapt to the friction reducer application's dilute polymer state.
Response surfaces were generated for various anionic, cationic, and amphoteric friction reducers with testing variables including brine type, loading, mixing rpm, mixing duration, shear rate, linear shear strain, responses of viscosity, and moduli with corresponding cross over results. Excellent regression was obtained from these complex, interactive response surfaces, revealing the breadth of variability obtained from complex experimentation and validating that studies using simplistic procedures provide limited and potentially biased performance conclusions.
When relating rheology to friction reduction and proppant transport, whether in the lab or the field, and understanding the complexities of polymer absolute dispersion, dissolution, and kinetics indicate that, with respect to performance prediction, limited knowledge is gained from simple polymer make down regimens. This work offers a guideline for assimilating comprehensive studies of complex versus oversimplified, limited scope rheological measurement research and analyses.