Downloads

This report describes in non-technical terms the various stages involved in finding and producing offshore oil and gas.

The process starts with geophysical surveys, which produce maps of the geology hidden beneath the seafloor. Seismic surveys are the most important geophysical technique employed.

Formations thought to contain oil and gas are identified from the seismic records and the most promising of them are then explored by drilling.

The type of drilling rig used depends on the water depth. Jack-up rigs are used in shallow water, up to a maximum of about 100 m water depth.

Floating rigs – semi-submersible rigs or drill ships - are used in deeper water.

The ways in which a well is drilled, cased and tested, the use of drilling muds, the control of pressure in the well, and the disposal of cuttings are discussed.

The discovery of sufficient amounts of oil and/or gas in exploration wells leads on to field development.

Many more wells are drilled at the field development stage – for producing the oil and gas, for the injection of seawater or gas in order to make the production more efficient, and for the disposal of materials which cannot economically be taken to shore (e.g. cuttings, produced water, gas).

Production facilities are installed – for example fixed or floating platforms and pipelines.

The different types of production platform and export facilities are described. The emissions to the atmosphere and the discharges to the sea generated in the production process are summarised.

Finally, after a production life which may last from less than 10 to more than 25 years, the production and export facilities are decommissioned.

This report was prepared by Hartley Anderson Ltd, an Aberdeen-based environmental consultancy.