Norman W. Hein, Jr., P.E.
Oil & Gas Optimization Specialists, Ltd. (now with NPS - Norris/AOT), Benny J. Williams, P.E. Harbison Fischer, Russell Stevens
Norris (now with Rod Lift Consulting), and Jim Patterson NPS
The sucker rod string for rod pumped wells can be adequately designed from hand calculations using API RP 11L1 or computer programs. While these methods will provide very good approximations of the loads and related stresses on the sucker rods and pumping system, they do not consider the loads the downhole equipment will be subjected to if a downhole pump is stuck and the rods are used to try to unseat the pump.
This paper will discuss the basic loads on the sucker rods when they are subjected to the fluid loads and forces when trying to unseat the pump. Additionally, results from testing downhole seating cups and mechanical bottom lock assemblies will be provided. Since the pulling unit weight indicator may not be accurate, the calculation converting unseating loads to maximum inches of pull or rod stretch will be provided. Recommended maximum pull weight on various grades of sucker rod diameters and grades will be provided from one sucker rod manufacturer. Finally, it is recommended that a check on the rig hoisting equipment (rod elevator and sucker rod hook) capacity is obtained to make sure the pulling system does not become overloaded when trying to unseat the pump.