Inhomogeneous flows of guar/metal ion gels observed by laser doppler anemometry and rheological measurements

Rheological and laser Doppler anemometry measurements on hydraulic fracturing fluids such as hydroxypropyl guar/titanate gels were conducted. These gels were prepared in both quiescent (batch mixed) and continuous shear (dynamically mixed) conditions. The lack of reproducibility of rheological data on both of these types of gels in parallel-plate geometry led us to build a laser Doppler anemometry/parallel-plate experimental setup to investigate the velocity profiles inside the gap. These measurements revealed (1) the existence of large-scale gel domains (also called gel particles) in the case of batch-mixed gels, (2) the absence of these large-scale domains in the case of dynamically mixed gels, and (3) strong edge effects. Based on these remarks, dynamically mixed gels showed reproducible rheological measurements in a Couette geometry when the edge effects were also eliminated.