Sand on Demand: A Laboratory Investigation on Improving Productivity in Horizontal Wells Under Heavy-Oil Primary Production

The cold-production recovery process, also known as cold heavy-oil production with sand (CHOPS), is a method for enhancing primary heavy-oil production by aggressively producing sand (massively and persistently). It is a successful commercial recovery process in western Canada using vertical (or slanted or deviated) wells. Applications of cold-production technology with aggressive sand production in horizontal wells, however, have not met with commercial success. This paper presents the results of experiments performed to assess the feasibility of applying cold heavy-oil production with horizontal wells using less-aggressive (i.e., controlled) sand-production strategies. Specifically, the effects of slot size, confining stress, fluid velocity, and sand-grain sorting on sand production have been investigated. Preliminary results indicate that slot-size selection is critical for establishing "sand on demand." For proper slot-size selection, it is essential to know the grain-size distribution of the sand-in particular, attributes such as the size of the coarsest fraction of the sand and the sorting (uniformity coefficient) of the sand. For example, it was observed in the sand-production experiments that the critical pressure gradient for maintaining continuous sand production is much lower for well-sorted sands (narrow size distribution) than for poorly sorted sands (wide size distribution). Ultimately, poorly sorted sands may require criteria different from those for well-sorted sands for slot-size selection. Flow rates are also crucial for managing sand production because a critical pressure gradient is required for initiating sand production and maintaining continuous sand production. The critical pressure gradient decreases as the slot width or confining pressure increases. Large permeability increases were observed in the sand-production region. Persistent sand production led to the growth of a channel and/or the presence of a dilated zone that had an elliptic shape.