Abstract:

The operating characteristics under low submergence depth and dynamic volumetric efficiency in the two phase gas and water flow will affect the pump performance and provide an important basis for the normal operation of sucker rod pumping system in the coalbed methane (CBM) wells. The mathematical model of dynamic performance for pump valve is developed based on valve dynamics and hydraulic friction. The operating performance and critical submergence depth are given due to the numerical solution and test results of valve open. And the variation of dynamic volumetric efficiency and efficient operating condition of sucker rod pump under reasonable submergence depth are analyzed based on the numerical solution and test results of operating performance. The results show that the hydraulic friction of pump valve is high during the opening moment. Its fluctuating frequency is fast and its amplitude quickly decreases in short time then becomes stable. The critical submergence depth increases from 2.55 m to 3.05 m while the pumping speed rises from 2.0 min^-1to 6.6 min^-1. The decrease of pumping speed and ratio of gas to water and increase of inlet pressure will enhance the water level and volumetric efficiency in pump. Furthermore, The increase of submergence depth will rise the pump efficiency rapidly, and then the pump efficiency increases slowly while it reaches to 70%~80%. The critical submergence depth is typically between 3.0 m to 6.0 m while the reasonable submergence depth is more than 15.0 m to 20.0 m in order to operate with high efficiency for the most pumps in the CBM wells.

Key words: operating performance, reasonable submergence depth, sucker rod pump, volumetric efficiency, CBM well