Abstract

Coiled tubing shear history effects on the rheological and hydraulic properties of various fracturing fluids are investigated using the experimental equipment available at the Fracturing Fluid Characterization Facility (FFCF), located at the University of Oklahoma. The primary investigation includes tubing curvature effects on the frictional pressure losses using various lengths of coiled tubing and on the fracturing fluids apparent viscosities, over a range of selected linear and crosslinked fluids, using a unique High Pressure Simulator (HPS), capable of operating at elevated temperatures and pressures. To ensure a comprehensive understanding of the curvature effects on the rheological and hydraulic properties of the selected fracturing fluids, both coiled and straight tubings are investigated. The results show that coiled tubing curvature increases the frictional pressure losses for fluids such as water, linear guar gum and Hydroxypropyl guar (HPG), and borate-crosslinked guar and HPG fluids. Also, the study shows that frictional pressure losses within a coiled tubing are dependent of coiled tubing shear history for borate-crosslinked HPG gels and are independent of coiled tubing shear history for borate-crosslinked guar gels. On the effects of coiled tubing shear on the rheological properties of the fracturing fluids, the study indicates that apparent viscosities of borate-crosslinked gels are a function of shear history, pH, and temperature. Furthermore, the results show that for certain fluids, there exist an optimum pH, where shear history does not affect fluid's apparent viscosity.

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