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Summary

Evaluation methods have been developed to detect cases of tubing/annulus communication. Temperature, spinner and noise logs, as well as fluid level detection equipment, are used under a variety of flow conditions. Step-wise procedures are provided.

Introduction

Production in the Prudhoe Bay Unit Western Operating Area (WOA) began in June 1977. Wells now flow naturally or with the aid of gas lift. Rates vary from 100 to 10,000 BOPD or more and gas/oil ratios (GOR) from 600-10,000 scf/STB. Water cuts have increased mainly in the waterflood areas and can approach 100%. The combination of water and 12% carbon dioxide in the dissolved solution gas forms carbonic acid, corroding tubulars despite corrosion inhibition treatments. A typical completion is shown in Fig. 1. Tubing sizes range from 3 1/2" to 7".

In the early years of field life few workovers were required. Most of these were to replace defective packers and thermocase tubing. An increasing number of mechanical failures of tubular components as well as worsening corrosivity of produced fluids has significantly increased the occurrences of tubing-annulus communication and corresponding workover requirements. In 1988-1989, 50 cases of tubing-annulus communication were found in the WOA. Of these, 5 were permanently repaired with wireline techniques and 3 were temporarily repaired until a workover could be implemented. The remaining 42 wells were shut in and worked over without attempting remedial measures.

This paper discusses methods used at Prudhoe Bay for identifying problem wells and determining the exact location of the leak in naturally flowing, gas lifted, and injection wells.