Incremental plunger force evaluation for predicting sucker rod buckling
Research output: Research › Master's Thesis
Buckling is an undesirable phenomenon occurring in sucker rod pumping. It essentially depends on the plunger load as a function of time, which is difficult to measure. Therefore a diagnostic tool has been developed with the goal to predict the rod string’s stresses downhole and hence its susceptibility to buckling. This is accomplished by running a dynamic finite element simulation on a chosen wellbore. The basic principle is to evaluate the plunger load incrementally by subsequently applying restarts of each individual time step. This restart procedure is then fully automated in a script. The procedure's accuracy can be adjusted by the user and is usually in the range of ±1kN. A great advantage of this diagnostic tool in comparison to other commercial software packages is that no interpolations or correction factors are needed and the actual trajectory of the wellbore can fully be implemented. Given accurate friction values at all relevant contact points, the evaluated plunger load corresponds to the Downhole Dynamometer Sensor (DDS) measurements carried out at the Chair of Petroleum and Geothermal Energy Recovery. With the presented methodology it is possible for every given wellbore to determine at what moment in time during the downstroke the plunger is under compression.