Gas Lift equipment selection is based on a few variables: tubing size, casing size, and surface capabilities. Depending on the drift ID of the casing and size of tubing, the selection of 1” or 1-1/2” valve will be chosen. Because conventional gas lift equipment has the valve made up on the outside of the gas lift mandrel, the OD of the station (mandrel + valve) is necessary in determining what valve size will fit within the drift of the casing.
When attempting to efficiently move production fluid from reservoir to surface, one key determining factor is fluid seal within the sucker rod pump. The right combination of plunger and barrel is essential to achieving fluid seal.
The amount of space between the plunger OD and the barrel ID is the fit. Proper fit is required to create fluid seal. If the fit is too tight, there won’t be enough lubrication between the components and the pump will become damaged very quickly in operation; too loose of a fit will result in lost production as excessive fluid slips down around the plunger on every upstroke, making a continuous loop within the pump.
In order to achieve proper fit, an assessment will be performed to establish pump operating depth, casing and tubing size, fluid properties (viscosity and solid content), size and type of surface pumping unit, strokes per minute, and production goals. This assessment will indicate which barrel and plunger combination is best suited for production.
After the appropriate combination has been selected, the barrel and plunger will be further evaluated. The barrel’s internal wall must be inspected for any pits or imperfections that can cause a disruption in fluid seal. Pits typically only emerge in barrels that have seen extensive field use in corrosive downhole conditions. In order to test a barrel, an ID air micrometer is used. The micrometer measures air flow utilizing the resistance created between the inner barrel wall and the micrometer barrel plug. The air resistance will remain constant unless a pit is encountered. After the barrel has been found to be free of any weak points, the plunger may be evaluated.