Proppant transport at the fracture scale: Simulation and experiment

Laboratory and field studies have demonstrated a strong correlation between the volume of proppant deployed in hydraulic fracturing operations and subsequent reservoir productivity. In recent years, the desire to improve proppant performance has led to the development of new generations of exotic proppants, as well as new propping strategies. Nevertheless, the factors controlling performance of even traditional proppants in real rock fractures are poorly understood. Improved models are needed to help devise optimal strategies for deploying traditional and new varieties of proppant. Large-scale proppant models frequently rely on empirical closure relationships to represent real-world transport behavior. However, care must be taken when applying such relationships outside their derived context. In particular, most models employ closure relationships determined for slurries where the fluid dimensions vastly exceed the particle size. This is not true for fracture flow, where wall effects alter the effective transport properties and introduce new interaction forces. This paper describes an ongoing study employing a combination of high fidelity numerical simulations and fracture-scale experiments to describe the transport properties of proppant particles in fractures. The experimental work examines proppant movement in clear-plastic three-dimensional reproductions of the shale surfaces recreated using three dimensional printing. These specially tailored flow cells are used in combination with micro-capsules for improved particle tracking in dense particle packs. The same shale surfaces are also employed in high-resolution particulate flow simulations in which both the particles and interstitial fluid motion are explicitly represented. The data gathered from these experiments and simulations are used to help constrain models of settling and dispersion in particle-laden fluids within fractures.