A Numerical Well Test Model for Fractured Wells in Fractured Shale Gas Reservoirs Considering Multiple Flow Mechanisms

Summary The reservoirs of shale gas are typified by their low porosity and permeability, which generally necessitates the implementation of large-scale hydraulic fracturing for economic development, thereby resulting in highly complex flow mechanisms. Well test analysis is an effective method for reservoir parameter inversion, which aids in the efficient development of shale gas. However, there is currently a lack of an efficient and accurate well test model for shale gas reservoirs. To address this issue, this study proposes a numerical well test model for fractured shale gas reservoirs that incorporates various flow mechanisms, including adsorption/desorption, diffusion, stress sensitivity, fracture closure, and non-Darcy flow. First, a transient transmissibility correction factor is introduced to account for fracture geometries and early-time transient effects, thereby enhancing model accuracy. Subsequently, the model couples gas transport equations with geomechanical effects and Langmuir isothermal adsorption, which are solved using the finite volume method combined with Newton-Raphson iteration. The subsequent step involves the validation of the model’s accuracy. This is achieved by comparing the model’s results with those derived from a standard software package. Sensitivity analyses further reveal that natural fractures reduce pressure loss by enhancing fluid supply, while adsorption delays the pressure decline at later stages; additionally, stress sensitivity and fracture closure intensify the pressure drop, particularly in soft shales. Moreover, the model identifies eight flow stages, including wellbore storage and skin effect, bilinear flow, linear flow, fluid supply, desorption, interfracture interference, transitional flow, and boundary-dominated flow. Finally, a field case study of a shale gas well in the Longmaxi Formation successfully matches production data, yielding inverted parameters such as matrix permeability and fracture conductivity. Overall, this work provides a powerful tool for shale gas reservoirs. The tool is capable of evaluating fractures, optimizing gas reservoir development, and interpreting well test data.