Hydraulic fracturing stimulates wells and has enabled exploitation of the vast unconventional hydrocarbon resources in the US and globally. Proppants, which are granular materials that prevent fractures from closing, must provide high fracture conductivities and withstand closure stresses without getting crushed. Advances in imaging technologies and high-performance computing enable calculation of transport and mechanical properties of pore-scale images. Imagebased mechanical and flow simulations can rapidly and accurately estimate the transport properties of proppant packs in fractures at different closure stresses, providing a credible alternative to difficult and expensive physical experiments.
This study examines transport properties of a ceramic proppant pack with confining stresses from zero to 20,000 psi. The images of this packing show rearrangement of the packing structure, embedding of the grains at the rock wall, and crushing of individual proppant particles. Lattice Boltzmann (LB) simulation results of this proppant pack indicate that the permeability and inertial flow parameter are sensitive to stress at high stresses (which crush the proppant particles) compared to lower stresses. Predicted stress-dependent permeability and non-Darcy factors corresponding to the effective stress fields around the hydraulic fractured completions are included in a two-dimensional gas reservoir simulator to calculate the productivity indices. Productivity indices with permeability and non-Darcy factors kept constant at initial effective stress (6000 psi) are ca. 0.03 percent higher than those with stress-dependent permeability and non-Darcy factors for a gas rate of 20 MMscf/D.