Stimulating Unconventional Reservoirs: Maximizing Network Growth while Optimizing Fracture Conductivity

TLDR

Unconventional reservoirs such as gas shales and tight gas sands rely on technology‑driven solutions—horizontal drilling, multi‑stage completions, innovative fracturing, and fracture mapping—to achieve economic production, which depends on matrix permeability and hydraulic fracture conductivity, with tight sands requiring less complex networks but still facing damage and zonal coverage challenges. Simulations show that ultra‑low shale permeabilities necessitate an interconnected fracture network with moderate conductivity and close spacing, and microseismic mapping confirms that such networks are achievable, with resulting production validating the models.

Abstract

Abstract Unconventional reservoirs such as gas shales and tight gas sands require technology-based solutions for optimum development. The successful exploitation of these reservoirs has relied on some combination of horizontal drilling, multi-stage completions, innovative fracturing, and fracture mapping to engineer economic completions. However, the requirements for economic production all hinge on the matrix permeability of these reservoirs, supplemented by the conductivity that can be generated in hydraulic fractures and network fracture systems. Simulations demonstrate that ultra-low shale permeabilities require an interconnected fracture network of moderate conductivity with a relatively small spacing between fractures to obtain reasonable recovery factors. Microseismic mapping demonstrates that such networks are achievable and the subsequent production from these reservoirs support both the modeling and the mapping. Tight gas sands, having orders of magnitude greater permeability than the gas shales, may be successfully depleted without inducing complex fracture networks, but other issues of damage and zonal coverage complicate recovery in these reservoirs. As with the shales, mapping has proved itself to be valuable in assessing the fracturing results.