Hydraulic fracturing conductivity relies greatly on settled proppant size distribution and coverage area of the fracture. In low viscosity fluid systems, such as water or slickwater, dune structures are frequently deposited inside the fracture with proppant injected first landing near the wellbore, while proppant injected later transporting further out into the fracture length. Several experimental and modeling studies have been conducted to evaluate this dune-forming behavior, and numerous field treatments are designed to use it to advantage.
This paper discusses the internal details of these dunes in light of the crossbeds that are created and the self-sorting of proppant particle sizes. Both behaviors can create streaks or layers of permeability within a dune structure and are similar in creation to geologic sedimentary structures created by Eolian and fluvial depositional systems. Such internal dune structures can degrade permeability within a fracture by forcing fluids to flow through baffles and potentially create barriers to flow. However, the self-segragation of proppant particle sizes may also lead to higher conductivities existing in a fracture than the bulk proppant sieve size may suggest. In either case, well productivity can be impacted and detailed modeling should consider accounting for these interdune structures.