Cold Production is a recovery process used in uncemented heavy oil reservoirs in which sand and oil are produced together under primary conditions. Sand production is known to be necessary in order to better access heavy oil reservoirs. The production of sand into a casing perforation was modelled experimentally using a horizontal sand pack. Heavy oil flowed through the sand and out the orifice at one end of the pack. The pack was scanned using an X-ray CT scanner. A high porosity (53%) channel (wormhole) was observed to develop in the sand pack above a critical pressure gradient. The sand cut was 44% (by volume) as the wormhole was developing. When the wormhole broke through the inlet, the sand cut decreased sharply. CT images taken at this time showed that only the loose sand within the wormhole started to be scoured away from the top down. The experimental observations suggest that the high sand cuts (20% to 40%) from wells at the start of cold production are due to the growth of wormholes while the sudden decrease in sand cuts (to 1% - 3%) indicates that the wormholes stopped growing. The residual sand cuts observed in the field are likely due to the scouring of the sand within the wormholes.