Performance Review of Tapered Submergible Pumps in the Three Bar Field
Authors: Swetnam J.C. , Sackash M.L. 
Published: December 2007

When lifting gaseous fluids with high-volume electric submergible pumps, compensation for compressibility and varying fluid volumes is required for the pump design. This paper describes the successful design and use of the tapered submergible pump for handling dynamic fluids in the Three Bar Field of Texas.

Introduction
The Three Bar (Devonian) Field waterflood project in Andrews County, TX, currently comprises 37 producing wells and 28 water injection wells. A total of 43 submergible pumps have been installed in 15 Three Bar Unit wells. Thirteen of the wells have used a total of 30 tapered pumps. This paper reviews the design, operation, and performance of these submergible pumps, with emphasis on the tapered submergible pump.
Submergible electric centrifugal pumps are used widely as a high-volume artificial lift method. There are many different sizes and types of pumps designed to handle specific volume ranges. A tapered submergible pump is any multistage centrifugal pump that is designed pump is any multistage centrifugal pump that is designed to handle a volume differential between pump intake and discharge, while remaining within optimum efficiency ranges. A single-pump type can handle a limited fluid volume differential. When a required volume differential exceeds the single-type pump's efficiency range, then two or more different stages may be incorporated into one pump. The pumps are assembled with the larger-capacity pump. The pumps are assembled with the larger-capacity stages on the bottom, or the intake, and the smaller-capacity stages stacked above. Although single-type pumps may handle differential volumes, for our purposes only pumps using two or more types in the design hereafter will be designated "tapered" pumps. Fig. 1 illustrates a complete down-hole configuration of this type.
On April 23, 1971, the first submergible pump, a tapered pump, was installed in the Three Bar Unit. Since then, submergible pumps have been responsible for recovering an incremental 1.84 million bbl oil more than the replaced rod-pumping equipment. About 66% of this volume was lifted by tapered submergibles. If this highvolume lift had not been introduced and operated successfully, many of these incremental reserves could have been lost because of failure to produce efficiently the volumes of fluid necessary to capitalize on the field's response to waterflooding.
Special emphasis on handling substantial quantities of gas with the high-volume lift equipment created the need to apply the tapered submergible pump design. A computer program was used to design the pumps at the Three Bar Unit. program was used to design the pumps at the Three Bar Unit. Although both the tapered concept and the computer-designed procedure are used widely and generally are accepted, this procedure are used widely and generally are accepted, this performance review of the pumps at the Three Bar Unit evaluates performance review of the pumps at the Three Bar Unit evaluates each type in practice.

Operating Conditions
The Three Bar Unit has experienced excellent waterflooding response, while producing from a Devonian limestone at an average depth of 8,200 ft. The reservoir has two pay zones with a total net thickness of about 70 ft. Both zones are highly fractured and each displays an average porosity of 20%. The crude oil is sweet with a gravity of 41 degrees API, viscosity of 0.371 cp, and bottom-hole temperature of 130 degrees F. The typical Three Bar Unit well under primary recovery was a flowing, high-GOR producer.
JPT
P. 1781