Repair of a Failed Gas Lift Completion Using a 1500 Ft. Long 3 1/2 in. Coiled Tubing Insert Straddle
Authors: Kinnear M.R. , John H. 
Published: December 2007

Due to tubular corrosion of a gas lifted completion on the Arbroath field, the well was unable to flow due to the well shallow gas lifting through holes in the tubing. Since the Arbroath platform is a rigless platform, a full workover was considered a costly operation with prohibitive lead times. For that reason less costly and innovative through tubing repair options were considered to allow the well to be returned to production. After considering several options a coiled tubing straddle insert was chosen as the preferred repair method to meet the success criteria for the job.

The straddle consisted of 3 1/2" coil with hydraulic set packers at either end and was successfully run inside the existing 4 1/2" completion to seal off the corroded section of tubing allowing the well to return to production. This paper describes the repair options considered, the design, planning and installation of the coiled tubing straddle and the subsequent post repair well results.

Introduction

The Arbroath Field lies in the central North Sea in Block 22/17 next to the adjacent Montrose field. It is an undersaturated oil reservoir and produces a 38 deg API oil from the Forties sandstone. Pressure maintenance is by means of water injection and natural aquifer support. The field currently has a total of 17 wells, 14 producers and 3 injectors with all the producers with the exception of one being produced using gas lift. Current production is around 45,000 b/d of oil and 11,000 b/d of water.

The Arbroath platform was designed as a not normally manned platform remotely controlled from the neighboring Montrose platform although it is currently permanently manned. It is a minimum facilities platform with the bulk of processing taking place on the neighboring Montrose platform. There is a single separator on the Arbroath platform where two phase separation takes place. Oil/water and gas are then sent via separate pipelines to the Montrose platform. for further processing. Injection water and gas lift gas are supplied via two further subsea pipelines from the Montrose platform making a total of four subsea pipelines running between Montrose and Arbroath.

The Arbroath platform was designed without a permanent rig onboard. The initial platform wells were drilled using a Giant Jack-up which was situated alongside the platform to allow the rig to skid across to the platform.

Arbroath Well Completion

A typical Arbroath well completion is shown in figure 1. It is a gas lift completion with gas lift gas injected down the 9 5/8" casing to tubing annulus. It comprises 4 1/2, L80 tubing with primary components of a production packer, expansion joint, shallow set annular safety system and tubing safety valve. The wells are installed with 7 gas lift mandrels fitted with annulus pressure operated gas lift valves and an orifice valve at the operating depth. The wells are operated with a surface gas injection pressure of 1500 psig. The wells originally flowed naturally from production start-up in 1990 but were put onto gas lift in late 1993/early 1994.

Background to Production Problems with Well T4 During late 1994 well T4 developed severe slugging problems and had great difficulty in flowing especially after a shutdown. T4 was flowing at around 3000 b/d of oil and a water cut of 30%.

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