Current sucker rod pump design procedures ignore calculating and comparing the pump's maximum available compression ratio with the required compression ratio of the installation. As a result, subsurface pumps are often installed with too small of a compression ratio for the production requirement. These pumps then experience chronic gas locking problems resulting in lost production and/or premature equipment failure.
This paper points out the need to consider compression ratio in addition to properly designed down hole gas separation as a critical part of a subsurface pump's design and installation.
The required and available compression ratios are both critical design factors for a rod pump installation when pumping live fluids. The discharge head of the pump divided by its suction head will yield the minimum required compression ratio of the installation. A combination of waste space or unswept areas, plunger diameter, and stroke length can all dramatically affect the pump's maximum available compression ratio. This paper will show that by simply modifying these factors and then recalculating the compression ratio available, a pump can be designed to exceed the minimum required compression ratio of the installation and still be capable of moving the desired fluid volumes. As this paper suggests, compression ratio calculations need to be included in the basic beam pump design calculations' for sucker rod pumping systems. By including them in this calculation, the sucker rod pumping system that is designed will be capable of operating without gas locking as long as it is spaced out properly when it is "hung on".
A subsurface sucker rod pump is a positive displacement (PD) pump. This subsurface PD pump, just like the multiplex PD pumps installed on the surface, has a required net positive suction head (NPSH) to keep the pump properly charged with liquid. This is required to provide proper run time. However, in normal oil field operations we often neglect this fact and have a tendency to over pump the wells in an attempt to maximize production.