Abstract

A submersible system is the most effective equipment for producing large quantities of fluid in a marginal environment. A miscible flood presents a unique set of conditions for operating submersible systems. Some of the conditions encountered include depth, small diameter well bores, high horsepower, temperature, gas production, power system disturbances, hydrogen sulfide, asphaltenes, and changing conditions.

The design of equipment, selection of materials, and operating requirements require special consideration. Techniques that enhance submersible performance are identified. Although none of these may be dramatic, the combination is dynamite.

The paper gives the operating conditions and experience with each component of the submersible system. The authors describe problems with and recommendations for selecting pumps, motors, seals, gas separators, cable, and variable frequency drives. Special attention is given to metallurgy, elastomers, training, and checklists necessary for successful operation. An extensive set of curves track the performance before and after changes.

Background

Submersible pumping systems are the most effective equipment for producing large quantities of fluid. In tougher environments, the submersible may be the only equipment that will survive the rigors of volume, depth, and temperature. The goal of this paper is to identify techniques that can be used to make this performance as effective as possible.

The Judy Creek Field is not an easy environment but operates on the edge of many constraints for submersible equipment. The field has a combination of problems that cause shortened submersible life. Some of these are depth, small diameter well bores, high horsepower, power system disturbances, temperature, gas production, hydrogen sulfide, asphaltenes, and changing conditions.

Previously, in an attempt to resolve some of these constraints, a variety of equipment was installed which included variable frequency drives, gas separators, tandem motors, flat cable with lead sheath, and various coatings. Nevertheless, the submersible run times in these conditions were still less than desired.

An outside submersible audit was conducted to identify changes that could be made. An aggressive agenda was established to bring the performance of submersible equipment to its potential. Consideration is given to the design, installation, and operation of submersibles in a marginal environment.

FIELD CONDITIONS

The Judy Creek Field is located in northwestern Alberta province of Canada. Production is from two pools in the Swan Hills platform. Major portion of the operations are from the 'A' pool, a reefal limestone complex of Upper Devonian age, while other production is from the 'B' pool, which is separated from 'A' by a well defined trending channel.

The reservoir is nominally at 8665 feet (2641 meters) and has a temperature of 205F (96C), with an API gravity of 41 degrees. Nominal bottom pressure is 3916 psig (27 Mpa).

A pattern waterflood in Pool 'A' began in 1974. A miscible flood using solvent injected with C2/C3 chase gas began in 1985.

Both the 'A' and 'B' pools have an average of 0.2% hydrogen sulfide. Chlorides are between 40,000 and 60,000 ppm. Asphaltine problems within the miscible flood are frequent and are treated with a xylene based solvent.

In addition the miscible flood causes dynamic operating conditions. The production can change dramatically in a short period of time. As the flood progresses to a producing well, the gas composition and production tends to increase significantly.

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