Until recently, the Progressing Cavity Submergible Pumping System (PCSPS) has only been used where a conventional top drive system was prone to frequent failure. However, recent studies on PCSPS applications have provided ample evidence that the PCSPS is an excellent alternative for many slant, deviated and horizontal progressing cavity pumping applications. The PCSPS with its proven longevity may also become a viable and economic method for vertical well progressive cavity pumping applications.
Evaluation of the retrieved downhole drive system from these applications has shown the units, in most cases, were in excellent condition and with minor tune-up and testing the equipment was again ready for service.
The progressing cavity pump made its first appearance in the Petroleum Industry in the 1970's by producing heavy crude oil with high concentrations of sand and solids. Since that time the application of the progressing cavity pump has expanded to include medium to light grade oil production as well as water source wells. In many cases the progressing cavity pump is the only viable method of lift in certain types of oil bearing reservoirs. This broader spectrum of applications and the relatively low capital cost and high system efficiency has significantly increased the use of progressing cavity pumps around the world. The increased use in a wide variety of applications has brought to light some of the deficiencies in the top drive progressing cavity pumping system. This paper will cover several field case studies illustrating the advantages of the bottom drive progressing cavity pumping system over the conventional top drive system.
Bottom Drive Progressing Cavity Pumping System - The PCSPS Progressing Cavity Submergible Pumping System (PCSPS) is a system consisting of a submergible motor rotating the progressing cavity pump from below, thereby eliminating the long failure prone sucker rod drive shaft.
There are several operational considerations in the development of the PCSPS.
The downhole components of the PCSPS consist of (in the order of well entry - Fig. 1): the Electric Submergible Motor, Protector, Gear Reducer/Flex Drive/Intake and Progressing Cavity Pump.
The Electric Submergible Motor for the PCSPS is a 4-Pole motor (Fig. 2) which has a full load operating speed of approximately 1700 RPM. The motors are currently available in the 450 series, 139.7mm (5–1/2") CSG and larger, 540 series and soon to be released 562 series for 177.8mm (7") and larger CSG. The 4-Pole (1800 RPM) motor was chosen over the standard 2-Pole (3600 RPM) product line because, in the opinion of Engineering and Manufacturing, the desired reliability and life expectancy could not be achieved with the 2-Pole 3600 RPM input speeds.
The protector is a Bag-Series-Bag-Series-Bag (BSBSB) type modular design modified for PCSPS applications (Fig. 3). The top chamber contains gear oil and the bottom two chambers contain motor oil. The protector is designed to provide a positive seal from wellbore fluids and the dissimilar oils, while equalizing internal motor and gearbox pressures to that of the wellbore The protector does not provide any thrust carrying capabilities.