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Abstract
Protecting the environment and health of the people by ensuring the integrity of all wells is one of the must-obey policies in Shell Petroleum Development Company of Nigeria Limited (SPDC). SPDC has been the leading producer of crude oil in Nigeria for more than 50 years. SPDC produces from many brown fields. SPDC currently has an inventory of producing wells that have been shut in because of one form or another of wellbore integrity problems. In some cases, these wells were completed decades ago when HSE requirements were considerably less stringent than they are today and wells were completed without sub-surface or downhole safety valves.

In 2003, a more stringent policy on non-integrity wells was introduced and led to an investigation of service providers for a more reliable rigless installation of safety valves or a more cost effective rig workover. However, most of the brown fields that encompass these wells are predominantly located in the Niger Delta both in the shallow waters offshore and in land locations including swamp areas. Many of the wells are located on small-unmanned production jackets which do not have the structural integrity to support even an electric line unit let alone a workover rig. In addition the current geopolitical situation in the Niger Delta is such that bringing in any heavy-duty equipment can be extremely difficult and highly uneconomical in most of these low producing wells.

It was against this background that SPDC carried out a well integrity management campaign to examine the feasibility of some kind of economic intervention to bring these wells back onto production.

In this paper the authors will examine in detail the prevailing situation, present details of the alternative solutions that were considered and describe a highly economic campaign that was put in place to rehabilitate some 40 wells and make available some 30,000 bopd of oil production, all without the use of major workover equipment.

Introduction
SPDC was incorporated in Nigeria in 1937 and was the pioneer in hydrocarbon exploration for several years before successful discoveries were made in the early 1950s. With their current production capabilities of approximately 1 million bpd of crude oil, it remains to this day the largest producer of oil and gas in Nigeria. The company produces approximately 50 percent of the total of Nigeria’s output from some 90 fields, which are concentrated in the land and swamp areas of the Niger Delta and in the adjoining shallow waters offshore (Refer to Fig. 1 for a map of the SPDC operational area in the Niger Delta). SPDC operates in a lease area of about 11,969 mi2 and has more than 3,728 miles of pipelines, 87 flow stations, 8 gas processing plants, and more than 1,000 producing wells.

Begun in 2003 and completed in 2004, SPDC conducted an audit that revealed many wells were producing without sub-surface safety valves and in excess of 200 wells were shut in due to various integrity problems such as outlined below:

• Failure to pass integrity tests due to leaks in the casing annulus, tubing leaks and leaking completion components such as packers, safety valves etc.
  
• Junk in the well or downhole fish stuck in the tubing.
  
• Wells, which were sanded in or in which the tubing was plugged with scale or paraffin, build up.
  
• Wells that were shut in because they had no emergency shut in device or safety valve. These wells were drilled and completed at a time when the strict HSE policies that are currently the norm were not in effect and there were no regulatory requirements for safety valves.