Agnew, I. Shell UK Exploration and Production UK

Introduction

The surface controlled subsurface valve (SCSV) is the final means of maintaining control of a well when all surface controls no longer function. Although it is seldom necessary to call upon the full services of this value it is essential that it does respond with 100 percent reliability whenever the need arises. When a completion is being designed particular attention should be placed on the selection of the SCSSV to ensure that the best choice of valve is made to suit the well conditions.

Summary

This report outlines the reasons behind the selection for the hydrostatically balanced SCSSV used by Shell Expro for their Northern Sea operations with particular reference to the Brent field. The main problem encountered with this valve was the very poor reliability due to elastomer seal failures. Initially the external chevron "Vee" packing came under close scrutiny and a wide range of materials were tested and tried with very little success. Internal "O" ring seals were also investigated and it was found that the combination of elastometer hardness, diameter clearance between sealing surfaces, surface finish and pressure differential across the "O" ring was critical to enable the seal to perform satisfactorily "T" seals the reliability of the valve is beginning to improve. The practicality of balanced type of SCSSV's is not very promising. Problems have occurred with live balance lines, promising. Problems have occurred with live balance lines, gased up balance lines and increased failure probability due to the extra seals which have to be used. The balanced type ball valve does have the added advantage of being able to cut piano wire, but this does not compensate for its poor reliability. piano wire, but this does not compensate for its poor reliability. Valve setting problems have been encountered but it is anticipated that they could be overcome by improving the techniques being adopted.

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