The production of sand grains from an unconsolidated porous solid matrix tinder viscous fluid flow is inevitable. While sand production has been found to effectively increase well productivity in both heavy oil and conventional light oil reservoirs, it can also lead to geomechanical problems such as sand failure and cavity (wormhole) formation. The paper investigates the phenomenon of sand production in a thick wall cylinder test that mimics both axial and radial flow near an oil well perforation. Then, an actual well section with perforations is analyzed with respect to sand production, failure, and cavity formation in the form of a wormhole. The numerical analysis is based on a reservoir-geomechanics model developed by the authors over the past several years. The model considers oil, fluidized sand, and sand phases interacting together through mechanical stresses and hydrodynamics within the framework of mixture theory. Interesting sand production mechanisms emerge from the interaction between geomechanics and an erosion process by which sand grains are detached from the solid matrix due to both fluid and stress gradients, once a certain level of material failure is reached.