Abstract

North Brae is the first North Sea gas condensate field to be developed using gas cycling for pressure maintenance and improved recovery Deviated wells have been drilled to depths of up to 18,900' MDRKB. Typical shut-in tubing head pressures (SITHP's) are in the region of 4,000 psi for producers and 5,000 psi for gas injectors. Moderate concentrations of CO2 and H2S at these pressures give partial pressures which cause a corrosive environment.

Coiled tubing (C.T.) well intervention in these conditions initially proved to be difficult. Failures of pressure control equipment and the C.T. itself were encountered. Despite this upgrading of equipment and improved procedures have allowed implementation of a highly successful C.T. programme at North Brae.

This paper provides information on the operational difficulties encountered, and resulting improvements made to overcome them. It outlines some of the equipment and technique upgrades necessary to ensure efficient and safe C.T. intervention in these difficult conditions,

Introduction

North Brae is a gas condensate field located in Block l6/7a in the UK Sector of the North Sea. Initial reservoir development, starting with first production in April 1988, has been to produce wet gas from the periphery of the reservoir and inject residual dry gas in the crestal area. Produced wet gas is separated on the Brae Bravo platform to yield liquid hydrocarbons which are exported. Crestal reinjection of the residual dry gas has been used to maintain reservoir pressure and improve recovery.

To date 19 development wells have been drilled including 4 injection wells Two horizontal production wells have been completed. Other production wells have maximum inclinations typically in the range of 40 to 60. All wells have 7" liners with production wells completed with 5 tubing, and injectors with 7" tubing. Perforated intervals are typically at depths between 12,500 and 15,500' MDRKB. The deepest North Brae well is 18,900' MDRKB.

By early 1990 it became apparent that scaling of the perforations and production tubulars was restricting production.

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