A Hybrid Transient Flow Model for Performance Evaluation of Shale Gas Reservoirs
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This thesis presents an analytical hybrid transient flow model (HTRF) for the performance evaluation of hydraulically fractured horizontal wells in shale gas reservoirs. The model assumes linear flow in the hydraulic fracture, the stimulated reservoir volume (SRV) and the unstimulated reservoir volume. We define a set of dimensionless parameters and apply diffusivity equations to real gas flow to quantify the effect of the SRV on gas production performance. It is assumed that the both the bottomhole flowing pressure and the average reservoir pressure decline with production time, until the constraint of the bottomhole flowing pressure is reached. We also consider the non-Darcy flow effect and the pressure-dependence of gas viscosity and compressibility factor. The comparisons between the proposed HTRF model, the trilinear transient flow model, and the trilinear pseudosteady-state model are performed to investigate the advantages of the HTRF model. Comparative sensitivity analysis shows that the HTRF model is suitable for common conditions of shale gas reservoirs in which matrix permeability could be as low as 10-4 md, natural fracture dominates flow mechanism, and bottomhole flowing pressure, average reservoir pressure, and production rate all decline with production time. The history-matching results with Haynesville shale field data indicate that the HTRF model properly matches the production history and effectively estimates seven key physical parameters, namely the hydraulic fracture half-length, natural fracture permeability, matrix permeability, natural fracture density, matrix compressibility, hydraulic fracture spacing, and well operating condition. The proposed model along with the history matching method is applicable to field-scale characterization and reservoir geometry quantification. It also serves as a tool to predict unconventional reservoir performance and the total recoverable gas.