Progressing Cavity Pumping System Applications in Heavy Oil Production

Abstract

Abstract Heavy oil and bitumen wells were traditionally produced with beam pumping systems. However, in the early 1980's, the introduction of progressing cavity (PC) pumping systems presented an alternative to beam pumps that possessed attributes which were ideally suited for heavy oil applications. The functional design of PC pumps facilitates the handling of viscous and abrasive multiphase fluids, and the lower capital and operating costs of these pumping systems makes them attractive for marginally economic operations. Today, primary heavy oil and bitumen applications are almost exclusively produced with PC pumping systems. To realize the benefits of PC pumping systems for heavy oil production, several issues must be considered. These include flow losses, sand production, rod string and tubing wear, low bottomhole pressures, power transmission/control and pump selection, sizing and reuse. Based on the results from numerical assessments, laboratory testing and field case histories, this paper presents system design, installation and operation guidelines which address these issues. Introduction Recent estimates characterize nearly 50% of the world's liquid hydrocarbon as having a gravity of less than 20 API. These reserves are generally referred to as bitumen and heavy oil. and large deposits are abundant in Canada, Russia, Venezuela and China. The most distinguishing characteristic of these fluids is their high viscosity which typically ranges between 500 and 15,000 cp for heavy oil and may approach 100,000 cp for bitumen. These viscous crudes are commonly located in shallow reservoirs (300 to 600 m depths) and individual wells usually produce these fluids at low to moderates rates (1 to 70 m3/day). In order to achieve economic production rates, most wells must be pumped at low bottomhole pressures which magnify the adverse effects of any produced gas. In addition, heavy oil and bitumen are typically withdrawn from poorly consolidated reservoirs which are prone to sand production that can exceed 30% by volume. The close well spacing required for viable field development often leads to the preferential use of directional and horizontal wells. Heavy oil and bitumen wells were traditionally produced with beam pumping systems, However, there were many problems inherent with these systems such as frequent sanding, severe equipment wear and low production rates due to rod hang-up. In the early 1980's, the introduction of progressing cavity (PC) pumping systems presented an alternative to beam pumps that possessed attributes which were ideally suited for heavy oil applications. Today, primary heavy oil and bitumen applications are almost exclusively produced with PC pumping systems. This paper reviews the application of PC pumping systems for artificial lift in heavy oil production. The benefits and challenges of utilizing these systems are highlighted. The main focus of the paper is on equipment design considerations and operational issues related to the production of viscous sand laden heavy oil. Results presented incorporate numerical assessments, laboratory testing and field case histories. PC PUMPING SYSTEMS Progressing cavity pumps are positive displacement pumps which consist of a helical steel rotor and a synthetic elastomer stator that is bonded to a steel tube. Rotation of the rotor within the fixed stator causes a series of sealed cavities to form and move axially from the pump suction to discharge. The resulting pumping action increases the pressure of fluid passing through the pump so that it can be produced to surface. Numerous papers describing PC pump principles and theory have been presented elsewhere. Most PC pumping systems are rod driven with the stator run into the well on the bottom of the production tubing and the rotor connected to the bottom of the rod string as illustrated in Figure 1.