Modelling of Sand Production From Wells On Primary Recovery

Abstract

Abstract 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. Introduction Several heavy oil producers(1–5) have recognized that producing sand with oil significantly enhances primary recovery. The widespread use of progressive cavity pumps has been a key factor in making the Cold Production process economical by reducing the damage to wells caused by the pumping of sand. Elkins et al.(1) were among the first to suggest that high permeability channels, which they called wormholes, develop in oil formations when sand is also produced. The wells were located in the Southeast Pauls Valley Field, Gavin County, Oklahoma. They inferred the presence of wormholes from tracer tests, caliper surveys of the well before and after sand production, permeability calculations and the large volume of sand produced. Vonde(2) reported a significant increase in oil production rates when wells, initially completed with 16 mesh (0.40 mm) liner slots, were recompleted with 250 mesh (6.35 mm) liner slots. The sand cuts also increased to 10% by volume. The wells they investigated were located in the Cat-Canyon Field, California. Injectivity tests, performed by Amoco, Canada(6), have shown that the concentration of an aqueous solution of flourescent dye did not change after being produced from an adjacent well. In a separate laboratory experiment, these investigators observed that the dye was adsorbed completely after flowing through a sand pack. Since the concentration of the injected dye did not change significantly in the injectivity test they inferred that the dye did not flow through a porous medium. They concluded that the dye flowed through a channel.Undiluted slugs of dye travelled at speeds up to 7 m/min. through what they believed were channel systems over 2 km in length that connected up to 12 wells(6). The wells were located in the Elk Point/Lindbergh fields, Alberta, Canada.