Abstract
This paper presents a method to correct results of laboratory measurements where we investigated the effects of wall slip, wall roughness and shear-induced slip on the viscous properties of crosslinked fracturing fluids. Our research indicates that crosslinked gels exhibit wall slip. The measurement of viscosity is dependent upon the surface roughness of the bob used in the tests. Unless an appropriate correction is made, the measured viscosity will be less than the true viscosity because of wall slip. Our study also demonstrates the occurrence of a rheological transition of polymer gel induced by shear forces. The critical shear rate, which we define as the beginning of stress transition from one state to another, may vary between 10-90 sec-1, depending upon the fluid nature, test procedure and temperature. Viscosities calculated using data from the different stress states at the same nominal shear rate can be different by a factor of 3 to 5. The gel with the higher critical shear rate exhibits more stable viscous properties when subjected to the thermal and shear degradation.
