Numerical investigation of multizone hydraulic fracture propagation in porous media: New insights from a phase field method

In this study, we use a phase field framework to examine multizone hydraulic fracture propagation in a poroelastic medium from a new perspective. Biot poroelasticity theory is used for coupling the displacement and fluid fields. We construct a total energy functional to include an additional pressure-related term, and achieve the governing equations of the phase field model by the variational approach. Darcy's law is used to model fluid flows in the calculation domain including the fully damaged (fractured) region. Two indicator functions based on the phase field are used to construct the relation between the properties of the intact and fully fractured media. The phase field method is implemented by using the finite element method as well as a staggered scheme for decoupling. After validating the phase field model in the example of a pre-cracked plaster sample with a circular hole, several numerical examples are presented to show the effects of multizone hydraulic fracturing treatment in the porous medium as well as the robustness of the phase field framework. These examples include an isolated hydro-fracture and multizone hydraulic fractures subjected to an identical fluid injection rate or pressure. Our simulations indicate that all possible fracture scenarios including fracture branching and coalescence, diverted, converging, and asynchronous fractures can be predicted by the presented phase field framework. The phase field model provides more insights that are hard to be gained through purely experimental tests and other numerical methods.