Prediction of Turbulent Friction in Rod-Pumped Wells

Abstract

Summary Frictional forces acting on a rod caused by a rod reciprocating in flowing fluid significantly affect the prediction and diagnosis of rod pumping system performance. Available studies of the flow in the tubing combined with moving rods and couplings are limited to laminar flow. The flow is more likely to be turbulent, however, for liquids with low viscosity and for regions near the rod couplings. Therefore in the current study, turbulent flow in the annular region between the stationary tubing wall and the moving rod/coupling is considered. Computational fluid dynamics (CFD) is used to simulate turbulent flow in the annular region with moving rods and couplings. Also, a simplified model using a mixing-length method is developed that is more computationally efficient than the CFD code. The CFD code that uses the standard k–ε model is used to predict turbulent friction factors in the annulus with the moving rods and couplings. The simplified model is developed to predict turbulent friction factors in the annulus with the moving rods. The results from these models are compared with each other and to the available data published. The friction factors between the rod/coupling and fluid can be represented by four parameters: the rod to tubing radius ratio, the coupling to tubing radius ratio, the fluid Reynolds number, and the relative rod velocity.