--> Hydraulic Refracturing Feasibility and Timing for Hydrocarbon Shale Reservoirs

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Hydraulic Refracturing Feasibility and Timing for Hydrocarbon Shale Reservoirs

Abstract

The unconventional shale reservoirs face a fast production decline through the primary depletion phase. A sustainable production from these resources requires production enhancement methods. Hydraulic refracturing is an emerging method that boosts the production through the expansion of areal contact between the well and the stimulated reservoir volume (SRV) around the wellbore. This paper will investigate two important aspects of the refracturing process: the prediction of production enhancement response and the optimum timing of refracturing process. A semi-analytical shale gas flow model with the desorption effect, referred to as the shale transient flow (STF) model, is developed to analyze and predict the production response to primary depletion, and is further expanded to predict the production response to the re-fracturing completions. The STF model is used to predict the estimated ultimate recovery (EUR) of the wells and determine the bulk characteristics of the reservoir and the well. The STF model is further tuned to predict the hydrocarbon production improvement and water production after the completion of a refracturing job at different times. The refracturing time is important from the technical and economic viewpoints. An early refracturing will reduce the efficient production from the existing hydraulic fractures. A late refracturing may not be supported because the reservoir pressure and the reserves are not adequate to support the capital expenditure. The optimum refracturing time depends on the reservoir and well characteristics. Some of these properties are subject to an uncertainty. A workflow is proposed to estimate the optimum time of refracturing based on the inherent uncertainty in the reservoir characteristics. The proposed methods are applied to the prediction of the well performance before and after the hydraulic refracturing in the existing and emerging shale hydrocarbon plays in the state of Texas, especially the Permian Basin. The validity of results is subject to the availability and quality of the input data; in this context, the limitations of the proposed model and workflow are discussed.