A Variable Speed Submersible Pumping System
Authors: Divine David L. 
Published: December 2007

A major new artificial lift system has been developed which will enhance the economics of many waterflood projects in West Texas and other recovery operations around the world. The new lift system consists of a standard oil well submersible pump and motor, a downhole pressure and temperature monitor and a static, pressure and temperature monitor and a static, variable frequency motor controller. The new system overcomes many of the problems associated with sizing larger lift equipment for secondary projects or any project in which an individual well's productivity may be hard to predict and maintain. The new system has predict and maintain. The new system has characteristics so different from a standard or constant speed submersible pump installation that it truly should be considered a new pumping system and not just an enhanced pumping system and not just an enhanced submersible system. The ability to control lift and rate with speed changes has dramatic effects on the submersible pump and motor. Equipment life is extended, the pump's operation range is extended, energy requirements are reduced, and very often initial artificial lift equipment investments are reduced. This paper covers the aspects and problems in sizing artificial lift equipment to point up the need for this producing system. The performance of the multistage deem well performance of the multistage deem well submersible pump and Motor when placed in a variable speed mode of operation will be addressed along with available test data which verifies that performance. Several implied system benefits such as extended cable and motor life and reduced impeller and bearing thrusts will be theorized and strengthened mathematically. The paper will also cover the system's lift efficiency and economic benefits as compared to equivalent constant speed submersible pumps and sucker rod pumps. Also to be presented is the history of the first field trial, installed in August of 1977.

Introduction

The downhole electrical submersible pumping system has been used in the oil field primarily in high volume lifting applications. The primarily in high volume lifting applications. The term "high volume" will have different meanings for different areas. If fluid is being lifted from formations at depths of 4500 feet or greater, then 600 to 700 BFPD may be high volume production. Generally speaking, an operator will look to the submersible pump in applications which extend beyond the range of a maximum size of conventional beam unit. High volume lift has been the principle use of the submersible even though submersible pumps are available to cover lift applications pumps are available to cover lift applications from 270 BFPD and up, at lifts up to 10,000 feet (total dynamic head). One of the reasons the submersible has not seen greater application is its lack of production flexibility once installed. Improperly sized equipment can lead to costly operations and early failures. It is the purpose of this paper to discuss the problems in sizing paper to discuss the problems in sizing submersible lift equipment and present an installed variable speed submersible pumping system which greatly extends the flexibility of the submersible pump.

SIZING THE CONVENTIONAL SUBMERSIBLE INSTALLATION

The most important consideration, and the least likely to be correct, in submersible pump sizing is the determination of a well's pump sizing is the determination of a well's productivity index, "J". Generally, engineers productivity index, "J". Generally, engineers will take one producing rate and an assumed Pr or two different producing, rates and determine a productivity index. Figure No.1 shows typical productivity curves based on the following data: Pr = Static bottom hole pressure = 2200 psia Pr = Static bottom hole pressure = 2200 psia Pwf = Producing bottom hole pressure = 1250 psia Pwf = Producing bottom hole pressure = 1250 psia qo = Producing rate at Pwf = 450 BFPD

Water Cut = 40%