Erosion and impact tests were performed on downhole valves with different materials to determine the best valve configuration for the field conditions.
Due to premature failures (less than 1 year of operation) in three wells caused by erosion of the valves, a complete investigation was conducted. First, the history of rod pumps installed in Caño Limón Field was analyzed to obtain configuration statistics of valves installed since 2005. Six different configurations were analyzed, including valves installed in failed and running wells. These configurations included six different ball metallurgies and two different seat metallurgies, combined in double valve setups installed in the pumps. The six valve setups were compared with the average run life and reservoir conditions to determine the best configuration for Caño Limón field. The statistics alone were not clear enough to determine the best configuration for the field, so a laboratory bench was designed to test the different ball and seat metallurgy configurations.
Silicon nitride balls were selected due to their resistance to abrasion, fluid cutting, and impact. The statistics showed good performance when installing silicon nitride balls with tungsten carbide seats, combined with titanium balls and tungsten carbide seats. But when installing single or double silicon nitride balls with tungsten carbide seats, the run time was less than 100 days. The laboratory tests were performed for titanium carbide, silicon nitride, and 440C balls, all of them with tungsten carbide seats. The erosion and wear tests were performed simulating the flow of a slurry around the ball. Silicon nitride balls showed less erosion than titanium carbide and 440C balls. The impact test was performed simulating the downhole pumping action, where the ball is impacted against the seat in a slurry made of water, polymer, and frac sand. Silicon nitride balls showed less wear than titanium carbide and 440C balls, but the seat working with silicon nitride ball showed higher wear than the other metallurgies. When installing single or double silicon nitride balls, the seat wear was higher than when combined when another metallurgy. It was possible to correlate the lab test results with the pump failures to determine the best configuration for the application.
When selecting the valve assembly's metallurgy, it is important to take into consideration not only the properties of the materials, but the effect of combining different metallurgies. Before standardizing an equipment change, field trials and lab tests should be performed.