The offshore oil and gas industry spends over $60bn per year on oil and gas wells and of this some $6bn, or around 10% is eaten up by geological and geotechnical problems such as stuck pipe, lost circulation, well bore instability, shallow water flows and other problems. On top of this are the environmental costs of the oil spills that can result from lost well control, and perhaps most importantly the human costs in terms of injuries and loss of life resulting from some of the worst incidents.
This paper lists the geohazards within and around a well, the drilling risks implied by these geohazards, and the impact they can have on the planning and drilling of offshore wells.
Current practice in geophysical and geotechnical site investigation techniques which, when correctly applied and interpreted, can help to reduce the risks and costs associated with the ‘Top-hole’ section is summarised and discussed (the Top Hole section is defined as the depth to the base of the first pressure containment string).
Finally, a systematic approach to assessing and mitigating top-hole geo-risks through a multi-disciplinary geoscience and engineering approach is described.
The authors are members of a working group of the Offshore Site Investigation and Geotechnics (OSIG) committee of the Society of Underwater Technology (SUT) who are drafting guidelines on the subject.
