Large-Volume, High-Horsepower Submersible Pumping Problems in Water Source Wells
Authors: Hoestenbach Roger D. 
Published: December 2007

Little has been written concerning problems that can be encountered in, or compounded by, installing large-volume, high-horsepower submersible pumping equipment in water source wells in the range of 30,000 to 90,000 BWPD at 320 to 1,020 hp.

This report addresses many problems of the past 12 years in Shell Oil Co.'s west Texas water supply system and the solutions that subsequently were applied. We feel that the majority of these problems are encountered in almost any project of this type. Motor, pump, and protector anomalies, accessory equipment, surface production facilities, and the protective schemes to optimize equipment life are discussed in detail.

Introduction

The project discussed in this paper is the El Capitan waterfield, which serves as the water source for the west Texas water supply system. The field is 8 miles northwest of Kermit, TX. The slightly brackish water, up to 600,000 B/D, is sold to 18 oil companies for waterflooding purposes in 49 projects in Ector, Andrews, and Midland Counties.

The field produces principally from the Permian reef complex, which is late Guadalupe in age. Lithology is limestone with dolomite, and talus characteristic of reefs. The Reef complex, 1,500 ft thick and 6 miles wide, is a horizontal collection of water with a total volume of 350 cu miles, 10% average porosity (a reservoir of 920 billion bbl of water), and 1 to 6 darcy permeability.

Discussion

Downhole Equipment (Fig. 1)

Electrical Motors

The submersible motors are two-pole, ±3,450 rpm. The 320-hp motor is a series duplexed tandem motor consisting of two 160-hp motors. The others are series triplexed motors - i.e., the 600-hp motor is made up of three 200-hp motors, referred to as upper tandem, center tandem, and lower tandem.

The 320-hp motosr have been in service since 1968. The 480- and 600-hp motors have been in service since 1973. They all are giving satisfactory service. The 1,020-hp motor is not yet in service but the application and installation engineering is complete, so it also is discussed where appropriate.

These large-motor assemblies are actually quite delicate from an applications point of view, and a complete understanding of their inherent design and operating characteristics is essential to the applications engineer. The long slender construction produces a motor with very unique characteristics; it starts extremely fast, saturates easily, develops large amounts of heat, has minimal insulation, has small radius, delicate stator end turns, has very low impedance, has high instantaneous locked rotor current, and is very sensitive to operating voltage, voltage unbalance, transient over-voltages and frequency of start/stop operations.

The current average run life in this particular project appears to be determined by three factors: 18-million-bbl pump throughput, 20 months' service, and/or 200 start/stop operations. These numbers have varied, often significantly, over the past 12 years, primarily because of manufacturing problems.

Full-voltage, across-the-line starting is used throughout the project. This has been dictated by economics, the quest for simplicity, and the desire to pass through possible torsional critical speeds as rapidly as possible.1 Full load speed is reached in 9 to 13 AC cycles (0.15 to 0.22 seconds) from the time the motor starter contactor closes. This obviously creates tremendous stress and thrust forces on the shaft assembly, the bearing surfaces, and the electrical components.

Downhole Equipment (Fig. 1)

Electrical Motors

The submersible motors are two-pole, ±3,450 rpm. The 320-hp motor is a series duplexed tandem motor consisting of two 160-hp motors. The others are series triplexed motors - i.e., the 600-hp motor is made up of three 200-hp motors, referred to as upper tandem, center tandem, and lower tandem.

The 320-hp motosr have been in service since 1968. The 480- and 600-hp motors have been in service since 1973. They all are giving satisfactory service. The 1,020-hp motor is not yet in service but the application and installation engineering is complete, so it also is discussed where appropriate.

These large-motor assemblies are actually quite delicate from an applications point of view, and a complete understanding of their inherent design and operating characteristics is essential to the applications engineer. The long slender construction produces a motor with very unique characteristics; it starts extremely fast, saturates easily, develops large amounts of heat, has minimal insulation, has small radius, delicate stator end turns, has very low impedance, has high instantaneous locked rotor current, and is very sensitive to operating voltage, voltage unbalance, transient over-voltages and frequency of start/stop operations.

The current average run life in this particular project appears to be determined by three factors: 18-million-bbl pump throughput, 20 months' service, and/or 200 start/stop operations. These numbers have varied, often significantly, over the past 12 years, primarily because of manufacturing problems.

Full-voltage, across-the-line starting is used throughout the project. This has been dictated by economics, the quest for simplicity, and the desire to pass through possible torsional critical speeds as rapidly as possible.1 Full load speed is reached in 9 to 13 AC cycles (0.15 to 0.22 seconds) from the time the motor starter contactor closes. This obviously creates tremendous stress and thrust forces on the shaft assembly, the bearing surfaces, and the electrical components.

Electrical Motors

The submersible motors are two-pole, ±3,450 rpm. The 320-hp motor is a series duplexed tandem motor consisting of two 160-hp motors. The others are series triplexed motors - i.e., the 600-hp motor is made up of three 200-hp motors, referred to as upper tandem, center tandem, and lower tandem.

The 320-hp motosr have been in service since 1968. The 480- and 600-hp motors have been in service since 1973. They all are giving satisfactory service. The 1,020-hp motor is not yet in service but the application and installation engineering is complete, so it also is discussed where appropriate.

These large-motor assemblies are actually quite delicate from an applications point of view, and a complete understanding of their inherent design and operating characteristics is essential to the applications engineer. The long slender construction produces a motor with very unique characteristics; it starts extremely fast, saturates easily, develops large amounts of heat, has minimal insulation, has small radius, delicate stator end turns, has very low impedance, has high instantaneous locked rotor current, and is very sensitive to operating voltage, voltage unbalance, transient over-voltages and frequency of start/stop operations.

The current average run life in this particular project appears to be determined by three factors: 18-million-bbl pump throughput, 20 months' service, and/or 200 start/stop operations. These numbers have varied, often significantly, over the past 12 years, primarily because of manufacturing problems.

Full-voltage, across-the-line starting is used throughout the project. This has been dictated by economics, the quest for simplicity, and the desire to pass through possible torsional critical speeds as rapidly as possible.1 Full load speed is reached in 9 to 13 AC cycles (0.15 to 0.22 seconds) from the time the motor starter contactor closes. This obviously creates tremendous stress and thrust forces on the shaft assembly, the bearing surfaces, and the electrical components.