Victoria Pons and Jeremy Gomes
WellWorx Energy
Objectives/Scope:
A new methodology for automatic iteration on viscous damping enhanced with state-of-the-art pump fillage, fluid load lines and valve openings and closing calculation is presented. Field results showing the impact of the methodology in diagnosing downhole conditions, improving inferred production, fluid level, pump intake and horsepower calculations are shown.
Methods, Procedures, Process:
The new approach uses a wave equation model with iteration on viscous damping paired with a traveling valve and standing valve calculation. Pump fillage and fluid load lines are calculated, which enables calculation of mechanical friction. The iteration uses a bisection method-like algorithm, which speeds up the convergence and removes the algorithm’s dependence on horsepower convergence criteria and other fluid and well variables.
Results, Observations, Conclusions:
In sucker rod pumped wells, efficiency and control of the entire system is ruled by elasticity, viscous friction and mechanical friction. Elasticity comes from the elastic behavior of the rod string and the propagation of stress waves due to the cyclic pumping operation traveling up and down the rod string at the speed of sound. Mechanical friction results from the rod string, couplings or pump coming in contact with the tubing. Viscous friction originated from produced fluid imparting a viscous force on the outer diameter of the rod string during operation. Those three factors are the basis for the calculation of downhole data from surface data to enable optimization and better control of sucker rod pump applications. Neglecting viscous friction leads to erroneous downhole data.
Very often, downhole cards have an over loop appearance which is physically impossible when considering pumping unit dynamics. This is due to the viscous force not being adjusted properly. Also, what can be mistaken from mechanical friction can be in fact completely removed from downhole data using appropriate viscous adjustment. Finally, operators traditionally overestimate their inferred production from the extra fictive load that is present on a poorly viscous friction adjusted card. The field data results presented in this paper show this new approach eradicates all these issues to deliver accurate and truthful downhole data.
Novelty:
The new approach iterates on the optimal damping factor for both the upstroke and downstroke for every stroke. Currently, most controllers utilize a manually adjusted damping factor, which leads to the damping factor not being adjusted for every stroke. Repercussions of this include overestimation of inferred production, overlooping phenomenon and appearance of excessive mechanical friction.