On the role of proppants and geomechanics on flowback behavior in complex fracture networks

Flowback analysis is often used for the post-fracturing characterization of unconventional wells to estimate key reservoir and fracture parameters. However, conventional flowback analysis relies solely on the fluid flow analysis, the potential impact of proppant or geomechanics on flowback behavior is seldom discussed. To fill this gap, an integrated numerical model is proposed here to simulate fracture propagation, well shut-in and finally flow back from fracture network. To simulate the fracture propagation with branches, a cohesive zone model with node displacement is adopted. During fracture closure process, proppant stress is integrated to consider the presence of proppants and non-linear fracture permeability evolution is also considered to represent the transition from fracture flow to Darcy's flow. Simulation results show that the presence of proppants and geomechanics may significantly impact the fracture closure mode and flowback behavior in fracture networks. When proppants are placed in the fracture, an infection point can be identified in the bottomhole pressure (BHP) response. After one day flowback, BHP with proppants is nearly 65% larger than that without proppants. Notably, fracture complexity can also be identified during flowback. As more proppants placed deeply into the fracture network, corresponding BHP would decline at a lower rate with later appearance of the inflection point. Besides, the formation properties near wellbore also affect the flowback behavior. As the permeability in the stimulated zone improves, BHP declines much milder after the inflection point. Finally, larger flowback rate can accelerate the fracture closure and enhance the overall BHP decline rate no matter when the inflection point is. Since most flowback models rely solely on fluid flow component, this study provides a new insight on flowback behavior which incorporate interactions of fluid flow, geomechanics and the presence of proppants.