Frac-pack completions have been used as a technique for well stimulation and sand control. Conventional hydraulic fracturing models based on linear elastic fracture mechanics often lead to inaccurate predictions of fracture geometry and fracturing pressure response due to large inelastic deformations and strong fluid-solid coupling. We present a fully-coupled, three-dimensional hydraulic fracture model with proppant transport in poro-elasto-plastic materials using a finite volume cohesive zone model for the frac-pack application.

We implement power-law fluid flow with proppant transport which accounts for proppant settlement, proppant retardation, and tip screen-out. Our model is capable of capturing the high net fracturing pressure during the simulation, shear and tensile failure around the fracture, and three-dimensional leak-off process. We observe that plasticity causes lower stress concentration around the fracture tip which shields tips of a propagating fracture from the fracturing pressure. Also, there are cells with a shear failure around the fracture and ahead of the tip due to the pore pressure diffusion. Cells tend to fail in shear first then in tension if sufficient pore pressure and poro-elastic backstress build up. We use three-dimensional numerical computation of fluid leak-off using two-domain coupling in this model to overcome the limitation of linear, one-dimensional leak-off model for high permeability reservoir. We investigate factors affect the pressure gradient such as the matrix permeability, injected fluid viscosity, and injection rate. Higher pressure gradient due to lower permeability, higher viscosity and injection rate results in faster propagation rate and steep declining pressure response.

LEFM models inherently predict lower net fracturing pressure, smaller fracture widths and longer lengths in soft formations than observed in the field. In many instances, such models are used to fit the net pressure data by manipulating input parameters beyond physically reasonable values. The model presented here provides a much more physically realistic approach to model fracture growth in unconsolidated reservoirs with lab measured mechanical properties and to understand the mechanisms of fracture growth. The model has allowed us to design and analyze hydraulic fracturing stimulations much more accurately than LEFM models used in the past.