--> Integrated Fieldwide Optimization of Wellbore and Hydraulic Fracture Placement in Shale Gas Reservoirs

AAPG Annual Convention and Exhibition

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Integrated Fieldwide Optimization of Wellbore and Hydraulic Fracture Placement in Shale Gas Reservoirs

Abstract

Unconventional gas resources are still considered marginally profitable and require careful economic assessment prior to field development. With current software tools, however, such assessment is only possible on well to well basis which does not always reflect the true economic potential of the unconventional asset. To bridge this gap and to provide the reservoir and production engineers with a tool that optimizes the number of horizontal wellbores and the key hydraulic fracture design parameters, we formulated, implemented, and tested a conceptually new integrated optimization framework. This framework takes from the user only minimal necessary input, which includes a shale gas geomodel and constraints on hydraulic fracture stage design, and calculates the optimal number of wells as well as locations, density, and half-length of the stages along these wells. Our novel integrated framework utilizes a stochastic evolutionary algorithm (GA with strong elitism) to evaluate the objective function of interest (e.g. discounted net present value of the project). The choice of the algorithm is dictated by its ability to find a nearly global maximum and physically sound production design in acceptable simulation time. The problem of finding the optimal number of horizontal wells, the number of transverse hydraulic fracture stages along them, and stage half-length is inherently discrete or mixed optimization problem. To address this peculiarity we formulate the framework as a fully binary evolutionary strategy that manipulates high-dimensional binary arrays encoding the number of wells and hydraulic fracture parameters. We investigate the range of applicability of our optimization framework and provide a large set of test cases and results for verification purposes. The proposed optimization strategy performs well for a given problem statement and finds the optimal solution that is consistent with the industry accepted and validated optimum for homogeneous matrix permeability fields.