Abstract

Electrical Submersible Pumps (ESP's) are being utilised on production platforms as a method of artificial lift for enhanced recovery of oil. With more subsea fields being developed, it is apparent that there will be a demand for this technology in subsea completions. This paper presents the technical issues involved with the installation of ESP's in a subsea completion and describes a system for low cost installation and recovery of the ESP without the requirement to recover the tree. The system utilises existing workover equipment and techniques to provide a safe environment for a tubing or cable suspended pump application.

Background

An oil producing reservoir has a natural pressure; however, this pressure may not be sufficient to start or sustain production flow throughout the life of a well. Secondary production flow throughout the life of a well. Secondary methods of extraction may be required to supplement the reservoir drive and raise the fluid to the surface. One method of extraction under consideration is the use of an ESP as a means of maximising production from a depleting or non-flowing well.

Subsea production fields are becoming more commonplace as exploration advances into deeper water, and secondary recovery systems will be an important consideration in the design of these subsea completions. Workovers will be conducted by semisubmersibles or multipurpose support vessels using diverless techniques. Without fixed overhead platforms, access to these wells will be very restricted. It is essential, therefore, that new tree designs and workover methods are developed to facilitate the use of ESP's in deepwater wells.

Introduction

The Subsea Submersible Pumping (S.S.P.) project has brought together a subsea equipment manufacturer, an underwater engineering contractor, and a submersible pump service company. Under technical supervision from pump service company. Under technical supervision from participating oil companies, the project has developed participating oil companies, the project has developed an overall system for a safe and cost efficient installation of downhole ESP's in subsea completions.

In the conceptual design phase of the project, the downhole equipment, subsea tree, and workover operations were studied and considered. It was concluded that two different pump systems offered the best potential for integration into pump systems offered the best potential for integration into a subsea completion: a tubing suspended system and a cable deployed system. It was also decided that wherever possible, the project would use field-proven equipment to possible, the project would use field-proven equipment to reduce technical risk and promote early acceptance and use of the system.

Key areas for development were identified as:

  • Subsea tree design

  • Power feed through the tree to the ESP

  • Workover

  • Subsea power distribution

SUBSEA TREE DESIGN

The subsea tree is considered the primary element in the establishment of a system. The tree design has major implications to the workover requirements and commissioning of the downhole pump. To this end, various styles of trees were evaluated for their suitability of an electrical submersible pump application.

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