Insights From Image-Based Modeling of Fluid Flow in Bulk Proppant Packs and Propped Fractures Under Varying Confining Stress

Ceramic proppant was imaged using x-ray computed microtomography (microCT) in three different geometries: bulk proppant, multilayer proppant pack between Berea walls, and single-layer proppant between shale walls. In all cases, the proppant packs were exposed to a range of confining stresses that varied between zero and 20,000 psi. The resulting microCT images were segmented, analyzed for structural and porosity changes, and then used for image-based flow modeling of low- and moderate-Reynolds number flow.

The images show expected changes as stress is increased: rearrangement of the packing structure, corresponding reduction in porosity, and some embedding at rock walls. At the largest stresses, individual proppant particles began to break apart.

Numerical simulation was performed using finite element and lattice Boltzmann methods. Results from both methods were used to compute permeability and Forchheimer coefficient (Beta factor) for the structures. Simulation results show reasonable agreement with experimental (vendor-reported) conductivity values (both permeability and beta). However, our results show that conductivity is less sensitive to loading than has been reported. Another somewhat surprising result is that fracture conductivity for the single-layer proppants confined between shale is similar to what would be predicted from bulk-proppant permeability, despite the significantly different flow geometry in the monolayer fracture. Possible reasons for this result as well as insights derived from flow visualization are presented in the paper.