One of the most fundamental, and often overlooked, subjects of pumping with a sucker rod pump is the influence of downhole pressure. There are 3 basic types of pressure that have direct influence on the ability of a sucker rod pump to work as intended; formation pressure (P1), internal pump pressure (P2), and hydrostatic pressure (P3).
The fluid level outside a sucker rod pump must be at or above the level of the standing valve of the pump in order to allow fluid to fill the pump chamber on the upstroke. This requires sufficient pressure from the formation entering the wellbore, continually pushing fluid above that level. If there is not sufficient pressure and the pump continues to operate, it will enter a pumped-off scenario. If this happens, the pumping unit should be shut down until sufficient pressure is present. This is a common occurrence in rod pumped wells and there are mechanisms to account for this such as variable speed drive pumping units, time clocks, and pump-off controllers. Alternatively, such as in an aging well, the seating depth of the pump may be increased (placed deeper) in order to continue to produce fluid at comparable rates.
Another pressure is where fluid is held in the tubing above the uppermost traveling valve of the pump, called hydrostatic pressure. There is no minimal amount of hydrostatic pressure that must be present in order for a sucker rod pump to operate effectively, it is simply a result of the system design.
The third type of pressure (internal pump pressure) is that which is felt by the pump. In instances where there is incomplete pump fill, perhaps due to insufficient pump intake pressure or gas interference, the pressures placed on the pump when the traveling valve meets the fluid are exponentially increased at the moment of impact to the point that components of the pump between the valves may burst or split.
Rod lift operations should be closely monitored to reduce the occurrence of undue internal pump pressure. Automation equipment has made these issues much easier to manage as well as innovations in downhole pumps and production tools such as the Oversized Cage
and Gas Separator
If you'd like help on solving this or any other rod lift issue, please contact the Don-Nan Tech Team