Laboratory-instrumented sucker-rod pump

Although sucker-rod pumps are installed in nearly 90% of all oil wells and many gas wells (for liquid unloading) in the United States and have been widely used for decades, there are many issues regarding their hydraulic performance that are not well understood. This is caused by the difficulty of obtaining downhole pump-performance data. Many persistent problems in sucker-rod pumping, including partial pump fillage, gas interference, gas locking, fluid pound, sticking valves, rod downstroke compression loading, equipment failure, reduced production, etc., are difficult to diagnose from the surface. Currently, verification of sucker-rod pump problems can only be inferred by removing the pump at great expense. Thus, root-cause analysis depends on guesswork and component analysis. Knowledge of pump characteristics downhole would allow problems to be predicted rather than simply diagnosed after they have persisted long enough to result in failure. To develop a knowledge base on sucker-rod pumps, a two-fold approach is being pursued: instrumentation of a clear sucker-rod pump in the laboratory, followed by the development of an instrumented downhole pump. The laboratory pump allows the development of diagnostic techniques in which pump performance can be verified visually. The downhole pump will allow testing at field conditions. A key element to both the laboratory and downhole instrumented pumps is measuring the compression chamber pressure (pressure within the pump barrel). The instrumentation has been designed to collect high-speed (greater than or equal to100 samples a second) data so that transient behavior (ball chatter, etc.) can be observed. Data is archived while the pump operates under various conditions, from full to pumped off. This paper presents results of tests with the laboratory pump that have resulted in new insights about pump friction and the techniques developed to measure dynamic and static pump friction. Analyses of the compression-chamber pressure are leading to a better understanding of what happens when both valves are closed and leading to the development of techniques to perform real-time diagnoses that determine fillage and gas locking. The laboratory data showed that compression-chamber data can be insightful in understanding pump conditions.