Reproducible rheological measurements on crosslinked fracturing fluids

Reproducible rheological measurements on crosslinked fracturing fluids are necessary to design fracturing operations and to evaluate crosslinked gel formulations. We present the results of cooperative tests on identical gel formulations (HPG polymers crosslinked with titanate and zirconate crosslinkers) run using different rehological instruments: Fann 50C, Rheometrics Pressure Rheometer, and a reciprocating capillary viscometer. With attention to 'dynamic mixing', temperature history, shear history during crosslinking, and flow field uniformity, it is possible to obtain comparable data from all three instruments. This has not been possible previously. The effects of temperature and shear history on the evolution of gel rheology is shown to demonstrate how these variables affect the reproducibility of measurments. Experiments on 'fast' and 'delayed' crosslinking systems show that delaying crosslinking until after exposure to high shear increases the viscosity of the gel.