A New Computational Fluid Dynamics Model To Optimize Sucker Rod Pump Operation and Design

Abstract

Artificial lift systems are widely used in oil production, of which sucker rod pumps are conceptually among the simpler ones. The reciprocating movement of the plunger triggers the opening and closing of two ball valves, allowing fluid to be pumped to the surface. Their built-in ball valves are subject to long-time erosion and fail as a consequence of this damage mechanism. Understanding the principal damage mechanisms requires a thorough examination of the fluid dynamics during the opening and closing action of these valves. In this article, we present a fluid-structure interaction model that simultaneously computes the fluid flow in the traveling valve (TV), the standing valve (SV), and the chamber of sucker rod pumps during a full pump cycle. The simulations shed light on the causes of valve damage for standard and nonideal operating conditions of the pump. In particular, our simulations based on real pump operating envelopes reveal that the so-called “midcycle valve closure” is likely to occur. Such additional closing and opening events of the valves multiply situations in which the flow conditions are harmful to the individual pump components, leading to efficiency reduction and pump failure. This mechanism, hitherto unreported in the literature, is believed to constitute the primary cause of long-term valve damage. Our finite element method-based computational-fluid-dynamics model can accurately describe the opening and closing cycles of the two valves. For the first time, this approach allows an analysis of real TV speed versus position plots, usually called pump cards. The effects of stroke length, plunger speed, and fluid parameters on the velocity and pressure at any point and time inside the pump can thus be investigated. Identifying the damage-critical flow parameters can help suggest measures to avoid unfavorable operating envelopes in future pump designs. Our flow model may support field operations throughout the entire well life, ranging from improved downhole pump design to optimized pump operation or material selections. It can aid the creation of an ideal interaction between the valves, thus avoiding midcycle valve closure to drastically extend the mean time between failures of sucker rod pumps. Finally, our simulation approach will speed up new pump component development while greatly reducing the necessity for costly laboratory testing.