Victoria Pons
Liberty Lift
In sucker rod pumps, work at the surface is translated to the pump downhole using a polished rod and rod string. Three factors reduce the energy available at the pump and decrease the efficiency of the rod pump installation.
The first factor is elasticity. Due to the elastic nature of the rod string and the cyclic motion of the pumping unit, stress waves travel up and down the rod string at the speed of sound, reducing the pump stroke and the efficiency of the downhole pump.
Secondly, viscous friction issued from the produced fluids, which impart a viscous force on the outer diameter of the rod string, further dampen the rod string’s movement.
Lastly, due to the deviation in a well, mechanical friction occurs when the rod string, pump or couplings come into contact with the tubing producing a normal force and drag friction that further slows down the movement of the rod string and reduce pump action.
In the great majority of models available to the industry, viscous friction is not adjusted properly, while mechanical friction is not addressed at all. In this paper, results from Liberty Lift’s proprietary diagnostic model are discussed comparing the mechanical and viscous frictions in different Permian and Bakken wells.