Zhaoqi Fan* and Daoyong Yang, University of Regina, and Xiaoli Li, University of Kansas Summary 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 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. This was a confirmation that the proposed sandfailure criterion can be used to characterize the sand production in a CHOPS process. Introduction In a heavy-oil reservoir, the sand flux along with the oil flowing into wells has been proved to surprisingly stimulate oil production (Smith 1988). With the advance of progressing-cavity pumps that enable the mixture of oil and sand to flow effectively, CHOPS has been extensively applied to the primary development of unconsolidated heavy-oil reservoirs in western Canada (Huang et al. 1998; Tremblay et al. 1999; Han et al. 2007; Sharifi Haddad and Gates 2015). The CHOPS wells can be found in Lloydminster Field, Provost Field in the Cold Lake Oil Sands Area, Lindbergh Field, Elk Point Field, Frog Lake Field, and in China and Kuwait (Huang et al. 1998; Dusseault 2002; Meza Diaz et al. 2003; Du et al. 2009; Sanyal and Al-Sammak 2011). The CHOPS process can be considered as an effective pretreatment for heavy-oil reservoirs before traditional thermal enhanced-oil-recovery (EOR) techniques and solvent-based injection methods because of the propagation of the wormhole network (Shokri and Babadagli 2012). Most of the sand is commonly produced during the first several months of a CHOPS well life, and the oil-production peak is usually later than the sand-production peak because of the coupling influences of sand production together with pressure depletion (Huang et al. 1998). Physically, high-permeability channels (i.e., wormholes) and foamy-oil flow are considered to be the main mechanisms dominating the CHOPS processes (Huang et al. 1998; Wang and Chen 2004; Tremblay 2005).