Optimizing Managed Pressure-Drawdown Flowback for Shale Gas Well with Complex Fracture Network with Fracture Closure and Two-Phase Flowing

Shale gas reservoir is fractured formation with hydraulically fracture network surrounding the shale matrix. Two-phase (water/gas) flowback schedule of fractured well is designed without a sufficient understanding that how the BHP-drawdown the well productivity. A two-phase coupled model is established to simulate the transient gas- and water-production from complex fracture networks. In this work, a new model was established to account for unique transport mechanisms. Different properties of flow mechanisms are assigned to fracture-network domain, stimulated-reservoir-volume (SRV) domain, and non-SRV domain. SRV is characterized by primary- and secondary-fracture network with different propped conductivities along horizontal wellbore. Non-SRV is described by several sets of isolated discrete fractures associated with dual-porosity system. The model is solved by numerical approach for performance forecasting. Embedded discrete fracture modeling (EDFM) and black-oil simulator are used to improve the computational efficiency. By using the numerical model, an efficient framework is established to obtain the optimum flowback scenario based on EUR maximization by using high-dimensional parameter design of experiment. The results show that the effective conductivity deteriorates with the decreases of pressure and water saturation in fracture network during two-phase flowback. The optimum flowback strategy enhances the peak of gas production rate and diminishes the dewatering time simultaneously. Meanwhile, the stress sensitivity contributes to the decreasing of network conductivity, and a more conservative drawdown is suggested for the fracture network with more stress-sensitive conductivity.