Abstract

Coiled Tubing Is used in over 1000 operations a year in the western half of the Prudhoe Bay Unit Fishing operations, well cleanouts inflatable packers end bridge plugs. cement squeezes, logging, N2 lifts and let pump operations are routinely performed year round Special considerations taken into account include temperatures to -60 degrees F. winds to 100 mph and the environmental sensitivity of the area.

Since 1980, when coiled tubing was first used at Prudhoe, it's use has expanded from simple corrosion inhibitor and acid pumping treatments to include the full range of operations pumping treatments to include the full range of operations listed above. In this time frame procedures have been worked out to ensure safe, trouble free operations. Accounting for the extreme environmental sensitivity of the area, for example, all rig ups employ flanged connections from the wellhead to the four ram BOP stack. Limits have been set on coil longevity and BHA's (Bottom Hole Assemblies) use safety equipment including hydraulic releases end check valves.

It is the purpose of this paper to discuss the evolution of coiled tubing operations in the WOA (western operating Area) of the Prudhoe Bay Unit Upon completion of the paper one will have Prudhoe Bay Unit Upon completion of the paper one will have an excellent understanding of the wide range of uses for coiled tubing and the type of equipment procedures necessary to do the job.

Introduction

Coiled tubing continues to be viewed with suspicion by many in the industry, believing that if you run it, you will not get it out. While this was true not long ago, it does not reflect todays equipment. Coiled tubing, when handled properly, is fast, economic end sale, it provides an excellent stepping stone between a wireline unit and a workover rig. Since its initial use in the WOA in 1980, CTU's (Coiled Tubing Units) and the coiled tubing itself have been greatly improved. Initially, problems were common with frequent coil breaks and pinholes in the coil. In spite of these problems however, potential benefits were obvious. Coiled tubing's mobility and trip speed, combined with a relatively low day rate was an incentive to work with the coiled tubing contractors to further develop this technology.

Since that time improvements in equipment, coil quality control, manufacturing techniques and operating procedures have resulted in an extremely reliable, cost effective and safe operation. Over 1000 coiled tubing operations per year are now performed with less than 6 partial to complete coil breaks per yew and no more than 3–4 incidents where coil is stuck per yew and no more than 3–4 incidents where coil is stuck resulting in a cutting and braided line fishing operation.

This paper's objective is to illustrate the wide range of applications coiled tubing is capable of performing. In support of this, discussions will first review job types routinely performed; the second section will cover the makeup of CTU's performed; the second section will cover the makeup of CTU's used on the North Slope and discuss some of the testing done on the coil providing the confidence to do many of the jobs performed today. The third section covers required safety performed today. The third section covers required safety checks for the coil, rig up and wellbore conditions. The final section is a brief discussion of what is done when the coil develops a surface leak or is stuck or left in the well.

COILED TUBING APPLICATIONS

Underreaming: The majority of soft unconsolidated fill cleanouts can be performed by circulating or reversing water and polymer sweeps through the fill. A downhole motor and underreamer are used when hard consolidated fill is encountered. Fifty three underreaming jobs were done during 1990 in the WOA of Prudhoe.

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