Petroleos

Chapter 7

Electric Submersible Pumps
W.J. Powers, TRW Reda Pump Div.

Introduction
The electric submersible pump (ESP), sometimes called “submergible, ” is perhaps the most versatile of the major oil-production artificial lift methods. This chapter provides the reader with a broad understanding of the key factors in selection, installation, and operation of electric submersible pumps. ESPtopics covered include the ESP system; applications; ESP system components; selection data and methods; handling, installation, and operation; and troubleshooting. ESP’s usually do not require storage enclosures, foundation pads, or guard fences. An ESP can be operated in a deviated or directionally drilled well, although the recommended operating position is in a straight section of the well.Because the ESP can be up to 200 ft long, operation in a bend or dogleg could seriously impact unit run-life and performance by causing hot spots where the motor rests against the casing. The ESP can operate in a horizontal position. In this case, run-life will be determined by the protector’s ability to isolate well fluid from the motor. ESP’s are currently operated in wells with bottomholetemperatures (BHT’s) up to 350°F. Operation at elevated ambient temperatures requires special components in the motor and power cables capable of sustained operation at high ambient temperature. ESP’s have efficiently lifted fluids in wells deeper than 12,000 ft. The pumps can be operated in casing as small as 4.5 in. OD. Many studies indicate that ESP’s are the most efficient lift method and the mosteconomical on a cost per lifted barrel basis. System efficiency ranges from 18 to 68 %, depending on fluid volume, net lift, and pump tn= The major disadvantage of the ESP is that it has a narrow producing rate range compared with other artificial lift forms. It does handle free gas well, but the impact of large volumes of gas can be destructive to the pump. Run life can be adversely affected by apoor quality electric power supply, but this is not limited to the ESP.

ESP System
The ESP system comprises a downhole pump, electric power cable, and surface controls. In a typical application, the downhole pump is suspended on a tubing string hung on the wellhead and is submerged in the well fluid (see Fig. 7.1). The pump is close-coupled to a submersible electric motor that receives powerthrough the power cable and surface controls. The ESP has the broadest producing range of any artificial lift method. The standard 60-Hz producing range of the ESP extends from a low of 100 B/D of total fluid up to 90,000 B/D. Variable-speed drives can extend the producing range beyond these rates. Although most operators tend to associate ESP’s with “high volume” lift rates, the average ESP producesless than 1,000 B/D of total fluid in continuous operation. ESP’s are used to produce a variety of fluids and the gas, chemicals, and contaminants commonly found in these fluids. Currently ESP’s are operated economically in virtually every known oil field environment. The WOR is, in general, not significant in assessing an application. Relatively high gas/fluid ratios can be handled using“tapered” design pumps and a special gas separator pump intake. Aggressive fluids (those containing HzS, CO?, or similar corrosives) can be produced with special materials and coatings. Sand and similar abrasive contaminants can be produced with acceptable pump life by using specially modified pumps and operation procedures.

Applications
The ESP historically has been applied in lifting water or lowoil-cut wells that perform similar to water wells. However, within this seemingly narrow segment there are many types of installations and equipment configumtions. This section covers typical installation, booster and injection, bottom intake/discharge, cavern storage/ shrouded configuration, and offshore platforms.

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