RHEOLOGY OF HYDRAULIC FRACTURING FLUIDS: SLIP AT THE WALL WITH SOLUTIONS OF HYDROXYPROPYL GUAR CROSS-LINKED WITH BORATE ION

Wall-slip (violation of the zero velocity at the wall boundary condition) has been shown to make significant contribution to the flow of solutions of hydroxypropyl guar cross-linked with borate ion.;Both batch and continuous cross-linked gels show significantly different shear stress with the two rheometers for the same shear rates. Hot-film anemometry was utilized with batch cross-linked gels. The heat flux from the hot-film anemometer probe which was flush-mounted with the wall also reflected the differences in flow response for rough and smooth rheometers. A smaller pressure drop was always accompanied by larger heat transfer rates during constant rate laminar flow. The theoretical model has shown has slip reduces momentum transfer and increases heat transfer, thus invalidating conventional transport analogies. This relationship was used to interpret simultaneous heat transfer and pressure drop measurements. Pressure drop data with continuously cross-linked gels show strong shear history dependency. The data show a smaller wall-slip velocity when cross-linked under higher shear rates. Indications of stick-slip behavior were observed with all of the partially cross-linked gels.;The cross-linking reactions were run both in a batch mode (no shear during the reaction) and a continuous shear mode. Wall-slip was observed in both cases. Two slot flow rheometers, one with a rough and one with a smooth surface, were used for the tests. Each of the devices were equipped with a set (three) flush-mount pressure transducers to measure the pressure drop due to flow and a flush-mount thin-film anemometer probe to measure heat transfer at the wall. Experiments with the roughened slot indicate that rough surfaces can inhibit wall-slip while smooth surfaces promote it. A comparison of the flow curves for the two flow channels indicates that the no-slip boundary condition was violated, thus producing wall-slip.