Drilling for offshore oil

The world produces over 100 million barrels of oil every day, much of it in harsh conditions, far from shore and safety if an emergency happens. So how is it done?

Oil has been around for millions of years, located deep below the land and sea where it became trapped under layers of permeable rocks or is slowly seeping to the surface. Although examples of oil drilling were documented in 4th-century China, the first modern oil-gathering structure was built in 1897, and by 1928 mobile rigs consisting of a simple barge with a drill mounted on top had set the scene for a revolution that fuelled Western industrial dominance for the next century.

Over 100 million barrels of oil are produced every single day, a process that usually starts with a range of surveys, from geographical and geomagnetic surveys to the deep echo sounding or seismic reflection surveys that pinpoint the likely location of a substantial deposit. Only then, and after the necessary permits have all been obtained, of course, can the rigs move in – multimillionpound structures and teams of professionals that locate, make the well safe and finally drill down to its precious commodity.

Today there are over 40,000 oil fields around the world, with most offshore drilling undertaken in the continental shelf – the sunken perimeter of a continent’s original glacial shape. From the $100 million monsters that plumb the deepest waters in the Gulf of Mexico to the smaller North Sea structures that nevertheless have to withstand 90-knot winds and 20-metre waves, mobile rigs are usually reserved for exploratory work, owned by private contractors and leased to the oil companies, who then have limited time to find, tap and process their precious bounty. Larger manned platforms and spars can service up to 30 wellheads, tapping into multiple wells up to eight kilometres from the platform itself.