Cold heavy-oil production with sand (CHOPS) has been one of the major recovery processes for developing unconsolidated heavy-oil reservoirs by taking advantage of sand production and foamy-oil flow. However, effective characterization and accurate prediction of sand production is still a challenge. In this work, a pressure-gradient-based sand-failure criterion is proposed for quantifying sand production and characterizing wormhole propagation. The proposed sand-failure criterion was initially developed at the pore-scale level, while a pseudointeraction force between two neighboring sand grains was proposed to implicitly represent the potential contributions of cementation and geomechanical stresses to the fluidization of sand. The criterion was then extended to a grid scale within a wormhole because the pressure gradient is constant at either a pore scale or a grid scale. With the bottomhole pressure being an input constraint, the proposed sand-failure criterion was validated with good agreement by reproducing production profiles and wormhole propagation from laboratory experiments and a CHOPS well in the Cold Lake Oil Sands Area. This was a confirmation that the proposed sand-failure criterion can be used to characterize the sand production in a CHOPS process.