Optimization of hydraulic fracturing design under spatially variable shale fracability

Current hydraulic fracturing designs are based on equal fracture intervals (spacing) along horizontal wells. Typical fracture spacing ranges from 50 to 600 feet while the fracture half-lengths normally vary between 100 and 600 feet. Symmetric spacing designs assume homogeneous shale mechanical property distributions, e.g. rock brittleness or fracability, which may not be the case in many shale plays. Fracability of the shale rock is an important property that controls the efficiency of the fracturing process. Therefore, the heterogeneity in shale fracability can have an important impact on the design and optimization of the hydraulic fracturing process. In particular, the optimal number, location, and length of the fractures can depend on rock fracability distribution. In this paper, we develop an optimization approach for hydraulic fracturing design under geospatial variability in shale fracability and investigate several aspects of the proposed fracture design optimization approach. In particular, we optimize the hydraulic fracturing design by implementing a variant of the Simultaneous Perturbation Stochastic Approximation algorithm to maximize the net present value of the shale asset, including the cost of fracturing and the revenue from gas production. The optimization framework provides a systematic design approach for hydraulic fracturing of unconventional reservoirs and can be applied to improve production efficiency and reduce the cost and environmental impact of hydraulic fracturing. We demonstrate the effectiveness and suitability of the proposed method using a series of numerical experiments in shale gas development.