Stochastic Modeling of a Fracture Network in a Hydraulically Fractured Shale-Gas Reservoir
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AbstractThis study introduces a novel approach to model the hydraulic fractures in a shale reservoir using a common stochastic method called random-walk. The goal of this work is to capture part of the complexity of a fracture/fracture network that has been generated by a hydraulic fracturing treatment and to attempt to characterize this fracture network using reservoir performance signatures.The steps involved in this work are:Stochastic generation of a random-walk fracture pattern constructed as a scaled numerical model. Assessment of the random-walk fracture using sensitivity analyses which consider the following elements: The tortuosity (i.e., the actual length to ideal length ratio) The tendency to branch (or split). The number of branching stages the number of branches was held constant for a given set of cases. Comparison of the mass rate and beta mass rate-derivative performance of the various random-walk fracture cases compared to the standard model of a planar fracture.The primary results of this work are:Generation of pressure distributions (maps) at given times (i.e., time slices) to qualitatively assess each complex-pattern during transient production. The pressure distribution figures (i.e., maps) are used to qualitatively determine the presence of fracture interference(s) and to identify a time interval where those interferences occur. Creation of a graphical correlation of reservoir performance in terms of cumulative recovery as a function of the fracture volume and fracture complexity (i.e., the number of branches). Creation of an empirical correlation between the number of branches in a given fracture pattern and the value of the mass rate beta-derivative during transient flow (we observed that the mass rate beta-derivative is essentially constant during transient flow regardless of the fracture network configuration, as such this constant value of the mass rate beta-derivative was selected for correlation).This work provides an alternative description of hydraulic fractures in unconventional shale-gas reservoirs which, in concept, captures the complexity of the hydraulic fracture as a stochastic fracture network.Early-time rate performance is believed to be an indicator of the geometry of the hydraulic fracture pattern. A fracture with a higher level of complexity yields higher values of mass rate beta-derivative when the fractures components are interfering with each other. Therefore, mass rate curves could be used as a diagnostic tool that helps the identification of the fracture geometric features.
