Abstract

The Conveyer Lift Pump is an alternative technology that uses viscous drag to lift liquids. The pump utilizes a flexible continuous rope or conveyer, affixed about a sheave at the top and bottom of the well moving upward inside the production tubing, viscously dragging or lifting the fluid from the well. Presented here are mathematical derivations for the flow rate, the quantity of fluid to be lifted, the required drag force at the rope surface, the power input required by the system and efficiency of this lift system. Two situations have been considered - firstly when the rope is centered in the tubing (concentric model) and secondly the off centre or eccentric model. Example cases demonstrate the efficiency of the model. Parameters include the rope and tubing diameters, different rope velocities and the fluid properties for particular well situations. Various cases are discussed and compared. Results from the models, shown with limited test data, indicate how to perform a more detailed engineering approach to analyze performance of this system for applications such as lifting fluids from shallow gas wells and for producing highly viscous fluids.

Introduction

Presented here is an analysis of an artificial lift concept, which is to 'Rope-Lift' liquids out of the wellbore, based on viscous drag between the moving rope and a liquid column in the annular space of the inner tubing wall and the rope. This differs from other methods of lift summarized by Brown (1).

Possible applications, which are illustrated, include lifting of oil/water from relatively shallow wells, the removal of liquids from gas wells to eliminate liquid loading (2), and the possible application of the concept to the lifting of viscous oil.

The foundation of the process is based upon mathematical models with the rope being centered in the tubing and being offcentre to varying degrees. See references (3)–(6) dealing with viscous flow in annuli and Lea (7) with a model of a downhole pump requiring some similar analysis. The mathematical model derivations and the end equations are presented. Simulation of sample cases, with rope eccentricity as a parameter, involving a range of tubing and rope diameters with varying viscosity have been calculated and presented here. Illustrated are the trends of overall system efficiency with various parameters, the motor input required, and liquid production for specific rope velocities. The relationships are made available to allow the user to optimize the concept for particular production conditions, but no attempt to optimize the concept in general is made here. The concept is discussed in detail by Crafton (8).

Discussion

The Rope-Lift pump consists of a flexible conveyor assembly using upper and lower sheaves in the well. This system could replace beam pump systems within the depth limitations of this concept. Coutte-Poiseuille flow principles are used to calculate the drag on an annular volume of fluid within the tubing id and the rope od moving upwardly resulting in well production. Proper selection of primary parameters of conveyor rope size and velocity and the tubing radial dimension are required to achieve an average upward movement of the fluid column.

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