A better understanding of the flow of sand and oil into slotted horizontal well liners is important for both thermal and non-thermal heavy oil production. The objective of this study was to investigate the structures that might form in and around a slot when sand production stops, and to relate the development of these structures to the porosity and, therefore, permeability increases within the sand pack. The parameters studied were slot size, sand morphology, and grain size distribution. Thin section analysis and X-Ray computed tomography (CT) techniques were used to observe sand packs immobilized with epoxy resin after sand production took place. The results suggest that sand production through the slots can be controlled, depending more on grain sorting than on the morphology of the grains or its average diameter. For a given sand type, sand production behaviour was strongly influenced by the arrangement of the sand grains observed in the vicinity of the slot, including the formation of sand bridges, arches, or plugs. X-Ray CT images showed that non-uniform porosity increases occurred in the pack, specifically in the area near the slot, when sand production took place. The porosity increases were less significant away from the slot. The magnitude of this increase was observed to depend on the quantity of sand produced and on the morphology of the sand. Good agreement was found in terms of porosity change between the thin-section observations and the CT-scanned images taken of the core before thin-section preparation.