Computational Fluid Dynamics Model to Improve Sucker Rod Pump Operating Mode

Abstract

Artificial lift pumps are widely used in oil production, and among them, sucker rod pumps are conceptually the simplest ones. The reciprocating movement of the plunger triggers the opening and closing of two ball valves, allowing fluid to be pumped to the surface. These valves are subject to long-time erosion and fail as a consequence of this damage mechanism. We demonstrate that understanding the principal damage mechanisms in the necessary depth and breadth requires a thorough examination of the fluid dynamics during the opening and closing action of the ball valves. This paper describes the basic ingredients and results of fluid–structure interaction model that simultaneously computes the fluid flow in the traveling valve, the standing valve, and the chamber of sucker rod pumps during a full pump cycle in an efficient and accurate way. The simulations provide necessary insight into the causes of valve damage for realistic standard as well as non-ideal operating conditions of the downhole pump. In particular, simulations based on real pump operating envelopes reveal that the phenomenon of so-called ‘‘mid-cycle valve closure’’ is likely to occur. Such additional closing and opening events of the ball valves multiply situations where the flow conditions are harmful to the individual pump components, leading to efficiency reduction and pump failure. The computational-fluid-dynamics model based on the finite-element method serves to accurately describe the opening and closing cycles of the two valves. Most importantly, this approach for the first time allows an analysis of real operating envelopes, derived from actual dynamometer cards. The combination of stroke length, plunger speed, fluid parameters, and velocity at any point inside the pump can thus be investigated at any time during the pump cycle. The flow parameters identified as critical in terms of damaging pump valves or other pump components can set the basis for taking measures to avoid unfavorable operating envelopes in future pump designs. Our comprehensive flow model may support field operations throughout the entire well life, ranging from improved downhole pump design to optimized pump operating modes and envelopes as well as in material selections. It is suggested to aid in adapting pump operating conditions to create an ideal interaction between the valves and avoiding the "mid-cycle valve closure". Specifically, a so-optimized pump design is expected to drastically extend the operation time before failure of sucker rod pumps. Finally, this type of simulation will speed up new pump or pump component development, and can eliminate or at least reduce the necessity of extensive and costly laboratory testing.