Page 436 - Hydrocarbon Exploration and Production Second Edition

Decommissioning 423

Figure 18.2 Awell before and after abandonment.

The production casing is cut and removed above the top of cement, and a cement
plug positioned over the casing stub to isolate the annulus and any formation which
may still be open below the intermediate casing shoe. If the intermediate casing has
not been cemented to surface then the operation can be repeated on this string.
Alternatively the remaining casing strings will be cut and removed close to surface
and a cement plug set across the casing stubs. On land the wellsite may be covered
over and returned to its original condition.
Traditional well abandonment techniques are being reviewed in many areas.
In some cases wells are being abandoned without rig support by perforating and
squeezing without cutting and pulling tubing and casing.

18.4.2. Pipelines
All pipelines will be circulated clean and those that are buried, or on the seabed, left
filled with water or cement. Surface piping will normally be cut up and removed.
Flexible subsea pipelines may be ‘reeled-in’ onto a lay barge and disposed of onshore.

18.4.3. Offshore facilities
There are currently more than 6500 oil and gas installations located on the
continental shelves of some 53 countries. About 4000 of these are in the US GoM,
950 in Asia, 700 in the Middle East and 400 in Europe.