Drilling in the Danish sector of the North Sea was on the point of being ha/fed by safety authorities recently, due to fear of a damaged casing. Only after the casing condition was verified by a new multi-finger caliper tool, was the operator permitted to continue unrestricted operations. In proving casing integrity, the caliper saved the operator significant expense in rig down-time, as wellas the technical risk involved in replacement of a casing string.

This paper describes the development and field test results of a family of caliper tools, one of which was used in the operation cited above. These calipers find applications in both casing wear and corrosion evacuation, and provide independent, real-time readout from each finger.

Sponsorship to develop the tools has been provided by the Drilling Engineering Association (Europe), under the DEA(E)-42 project. The DEA calipers am designed to give improved coverage, resolution and accuracy, in any fluid, over previous technology, as well as the providing the operator with a very rapid well-site answer.

Field test results presented in the paper, together with data from commercial operations (undertaken by Elf Enterprise Caledonia [EEC] and others), detail how the DEA calipers have:

  • Confirmed the development of wear grooves

  • Positively identified casing damage

  • Confirmed casing integrity to safety authorities

  • Monitored corrosion using time-lapse techniques

  • Uniquely identified causes of low productivity


'It is of vital; importance to be able to measure the shape and size of the wear groove both accurately and reliably. This is not possible with currently available logging tools stated David Boulter of the project's primary sponsor, 5P Research, at the outset of the project. He added 'From a safety standpoint a/one the industry naeds such a toof'.

Investigation of both casing wear, and general condition, is an aspect of well maintenance which has been limited to date by the technology available. With the development of the DEA calipers, it has become possible to provide the detailed and accurate date required for analysis of downhole tubulara.

During the drilling phase, the tool measures casing wearcaused by the rotating drill-pipe. This wear weakens the casing, which decreases burst and collapse pressures. Critical weakening or complete breakthrough can be prevented by monitoring casing wear, thus prompting the Petroleum Engineer to schedule intermediate casings at the required time. Field test results and commercial data acquired during the project have shown that drilling wear appears to be the norm rather than the exception.

During the production/injection phase, the tool allows accurate assessment of tubular condition. Damage or anomalies, such as wire-line wear, corrosion, erosion, holes, splits, ovalisation or oollapse can all be evaluated. Perforation mapping and enlargement monitoring is a further application, which can play an important part in the assessment of well problems. The high resolution data now available to the Petroleum Engineer is thus becoming an increasingly powerful weapon in the fight to reduce well maintenance oosts. At the inception of the DEA project, Sondex had been working on the development of a 40 fingered corrosion.

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