Design and Analysis of a Conveyor Lift Pump

Abstract

Abstract The Conveyer Lift Pump 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. Concentric and eccentric solutions are presented. Introduction and Discussion 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 (Figure 1). This differs from other methods of lift with details in References (1) and (2), and other methods summarized by Brown(3). Possible applications 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 centred in the tubing and being offcentre to varying degrees. For further details, see Reference (1) [Lea(2)] with a model of a downhole pump requiring similar analysis, and Crafton(4). The tubing on the upper end delivers the fluid that has been viscously dragged along with the rope, providing the rope speed and rope and tubing diameters and the fluid viscosity are selected to yield positive production. A rope housing supports the rope during its downward travel to prevent wear from rubbing on the casing. The fluid at the surface may have to undergo a slight "scraping" effect to prevent produced fluid from being carried back downhole. It appears that this could be used for sandy production as no sliding metal surfaces are employed, such as those found in a downhole beam pump. Also, it may be useful for high viscosity production, as the basic concept depends on fluid viscosity for lift to occur. If treating fluids need to be pumped downhole, those fluids can be conveyed to the sandface via the return protective tubing. Another application might be to pump relatively small amounts of liquid from a producing gas well to help eliminate liquid-loading. Full-scale field experience is in short supply. One weakness appears to be depth. Some of the illustrations below indicate the force needed at the surface of the lifting rope is calculated to be excessive as deeper wells are considered. Use of the models presented here should help the user evaluate the potential of this lift concept for various production scenarios. Models and Sample Result Models for the rope-lift pump were developed, including the rope being concentric in the tubing and also at various degrees of eccentricity.