Abstract
Transporting proppant deep into hydraulic fractures without settling is critical to success of hydraulic fracturing operations. The current capability to predict proppant transport for a given fracturing fluid is often limited to the power law model and Stokes equation without quantitative consideration of other important fluid property changes, such as elasticity caused by shear flow in the fracture. The goal of this study is to investigate the effect of shear flow on proppant settling over long time periods.
For this purpose, a multipass slot flow apparatus has been developed to mimic fracture flow. Unlike existing slot flow devices, the new apparatus is capable of running continuously and attaining a time scale more similar to a realistic fracturing treatment. The proppant transport behaviors of a variety of fracturing fluids, including linear and crosslinked gels, are investigated. For crosslinked gels, two types of crosslinkers possessing very different characteristics are examined. One uses borate ions, which react with polysaccharides to form a reversible and rehealing crosslinked gel. The other gel uses zirconium, which forms an irreversibly crosslinked gel with the same polymers. To probe the relative importance of elasticity and viscosity, samples with various viscosities and elasticities are formulated and their proppant suspending power is measured. It is demonstrated that these different fracturing fluids show dramatically different static and dynamic proppant suspending behavior, which is correlated to their rheological properties, including yield stress, viscosity, and elasticity. These findings can provide valuable guidance in terms of optimizing fracture fluid design to maximize proppant transport properties.
