This paper presents a coupled reservoir-geomechanics continuum model for sand production simulation around an open-hole and a cased & perforated wellbore in a weakly consolidated formation. Sanding criteria are based on a combination of tensile and shear failure from Mohr-Coulomb theory and strain-hardening/softening. Once the failure criteria are met, a new erosion criterion for entrainment of the sand based on the calculation of hydrodynamic and resistant forces on sand grains is implemented to predict sand erosion. To capture the strain localization, dynamic mesh refinement has been implemented in the model. An open-hole completion is first simulated to conduct a sensitivity study with both mechanical and fluid flow properties. Then, cased & perforated well completions are modeled to analyze the stability of perforations. Sand failure and production are induced primarily by stress concentration around the borehole and large gradients in fluid pressure. Several factors, including the perforation orientation, perforation arch stability, perforation diameter, and length of perforation, are shown to be important and are discussed. This model is able to predict the onset of sanding and the severity of sand production around wellbores and perforations, and help design perforated completions.