A fully coupled geomechanics and fluid flow model for proppant pack failure and fracture conductivity damage analysis

One reason of observed reductions in the conductivity of hydraulic fracture is failure of proppant pack under the stresses. Proppant deformation, crushing or embedment can decrease the fracture width and conductivity. In this paper, continuity equation and momentum balance equation were fully coupled to simulate the transient phenomena involving fluid flow through a deformable porous proppant pack. Porous media displacement, water pressure, and gas pressure were derived as primary unknowns. The governing equation was discretized using the finite element method and solved numerically. In this model, proppant pack and formation rocks were treated as two different types of continuous porous mediums (Biot type). Proppant deformation, crushing, and embedment could be identified through the geomechanical model, while the damage effects on gas/oil production would be studied through the fluid flow model. Analysis of proppant deformation and crushing was based on the proppant pack stress-strain behavior. The displacement on fracture-formation interface represented the proppant embedment. Mohr-Coulomb failure was used as the criteria for proppant crushing. Effects of proppant damage were evaluated on proppant pack porosity and permeability. The model can be applied in all the hydraulically fractured reservoir with proper inputs. In this paper, we used fractured tight sand gas reservoir as a study case. The pressure distribution as well as proppant pack deformation were illustrated in the paper. Proppant pack mechanical behavior was found to be sensitive to the fluid flow pressure and proppants near wellbore was under higher possibility of being crushed.