Dynamometer card of sucker rod pumps in coalbed methane wells

The dynamometer card can illustrate the variation of polished rod load and provide the basis for design calculation of sucker rod pumps in coalbed methane (CBM) wells. Based on the kinematic and dynamic analysis of the pumping system, the mathematical models of the loads of polished rod were developed. The static and dynamic dynamometer cards were obtained with every phase. The results show that the static dynamometer card is approximately the actual one during the steady flow production, shows the variation of static load and will help to analyze the actual one. The dynamic dynamometer cards present the shape of fluctuation and deflection due to the dynamic loads, and their upper and lower parts are removed from two ends respectively due to the friction loads. The ratio of the dynamic and friction to polished rod is calculated as 15% and 5% respectively, which increases the variation range. For dynamometer cards, their two parts deviate from the null line, the slopes decrease gradually, and the rangeability becomes smaller and smaller due to the low ratio of dynamic to polished rod load. Besides, the total string deformation in CBM wells is small and just 10% of stroke length. And the total and static deformations are enhanced while the dynamic ones decrease with the decrease of the pumping speed.