Abstract

Some clients of coiled tubing service companies increasingly demand inspection of the tubing immediately prior to or during field operations. There is a lack of suitable available equipment for inspection of tubing for wall thickness and ovality deficiencies, particularly where operation in potentially explosive atmospheres is required.

Technologies exist for the inspection of wall thickness and ovality in both maintenance facilities and on operational locations but are commercially available only as a third party service; only one such service is known to be certified for explosive atmosphere use and all require trained technicians.

This paper presents a new wall thickness and ovality measuring tool engineered for reliable field use and which needs no specialist inspection personnel. By combining custom-designed fiber-optical transducers and magnetic flux leakage (MFL) principles, electrical apparatus is eliminated from the explosive area and certification is not required. The unique fiber-optic system design contributes significantly to the ruggedness and reliability of the inspection system.

Performance data from field service will be presented.

Introduction

Coiled tubing (CT) is an established technology for performing a wide range of operations in oil and gas wells. The CT is subject to severe working conditions and may fail mechanically as a result of wear and defects. There has been a need for on-site real-time inspection of the CT as part of an overall quality management strategy for eliminating such failures.

There is a lack of suitable available equipment for the condition monitoring of CT, particularly where operation in potentially explosive atmospheres is required. Technologies exist for the inspection of wall thickness and ovality in both maintenance facilities and on operational locations but are commercially available only as a third party service; only one such service is known to the authors to be certified for explosive atmosphere use and all require specialist personnel.

This paper presents a new wall thickness and ovality measuring tool engineered for reliable field use and which needs no specialist inspection personnel. The tool uses fiber-optical transducers to exclude electrical apparatus from the explosive area, eliminating the need for certification.

Project Specifications

The intent was to create a tool to meet the operational needs of the users, with an emphasis on simplicity and convenience of use. The criteria were:

Measurement performance.

Diameter and ovality accuracy +/- 0.005".

Wall thickness accuracy +/- 5% in all carbon steel CT grades.

Detect localised metal loss to 5% on area 0.7 sq. in.

Shall not trigger alarms on small corrosion pits, cracks.

Environmental

Permissible to use in potentially explosive atmospheres.

All-weather -40 to +40 deg C.

Operational

Running speed 0 to +/- 200 ft/min.

Sensor assemblies to mount on standard level-wind trolley.

Sensor assemblies to be easily removable from CT.

Shall not require special cleaning or pre-treatment of CT.

Shall interface to existing data loggers installed in CT units.

Shall not require additional personnel.

Shall not require specially trained personnel.

Design concepts to meet specifications.

The need for operation in explosive atmospheres, particularly in the North Sea, was the overriding factor in selecting technologies for both the wall thickness and calliper tools. Any electrical component located outside of a safe area would need approval by certifying authorities. A search for certified wall thickness and diameter sensing components failed to find any suitable for integrating into a workable tool. While non-approved components could have been repackaged to meet required standards, qualified advisors concluded that the approval process would create unacceptable delays.

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