Previous experimental observations have shown the formation of distinct failure patterns and cavity shapes under different stress and flow conditions. With isotropic stress, spiral failure patterns with localized shear bands are likely to form. On the other hand, under anisotropic stress, V-shape cavities, dog-ear cavities or slit mode cavities are usually observed. However, the mechanisms for the development of these sanding cavities remain unclear. In addition, in order to accurately predict the onset of sanding and predict the sand production rate, it is crucial to capture the physics of formation of these cavities during sand production.

This paper presents a fully coupled poro-elasto-plastic, 3-D sand production model for sand production prediction around open-hole and perforated wellbores in a weakly consolidated formation. Sanding criteria are based on a combination of shear failure, tensile failure and compressive failure from Mohr-Coulomb theory and strain-hardening/softening. Once the failure criteria are met, an algorithm for entrainment of the sand based on the calculation of hydrodynamic forces is implemented to predict sand erosion and transport. Dynamic mesh refinement has been implemented to effectively capture the strain localization regions.

The model has been validated with multiple analytical solutions. In addition, it is applied to compare with previous sand production experiments that have explored the different cavity shapes formed under different conditions. The model is capable of not only explaining the mechanisms responsible for each type of cavity shape but also predicting what cavity shape will be formed under a specific set of conditions. Parametric studies for these cases provide additional insight into the important role that the post-yield, poro-elasto-plastic properties of the sand play in controlling the sanding mechanisms and cavity development. This allows us to much more accurately predict the onset of sanding and the sanding rate.