Big Rig

We have a love-hate relationship with oil

Oil is without a doubt vitally important in feeding the world’s insatiable appetite for power – yet we know that burning the dark and slimy liquid is polluting our precious planet.

But until the political will really exists to switch to cleaner and renewable forms of energy we are stuck with it. And there’s only one way to get at most of it: drilling deep into the earth’s surface.

Most of the world’s known reserves of oil, which stood at 1.317 billion barrels in 2007 according to the Oil and Gas Journal, are found under what is now dry land, but as the price of oil continues to increase, oil companies are exploring further and further offshore.

Getting to that offshore oil is obviously harder than drilling on land because the drilling sites are in up to 10,000 feet of water (3,048 metres: the oil industry still uses imperial measurements for depths) and hundreds of potentially stormy kilometres from shore. Safely housing all the equipment and people required to get at the oil requires a mega-structure known as an oil rig.

Going Deeper

A key player in the offshore industry is the Texas-based Diamond Offshore. One of the 44 rigs in its fleet is the Ocean Endeavor, a semisubmersible, Victory Class ultradeep- water rig currently drilling in the waters of the Gulf of Mexico. Originally built in 1975 to operate in water no deeper than 600 feet, the Ocean Endeavor last year completed an upgrade in Singapore to make it capable of drilling for oil in 10,000 feet of water.

While there’s still a degree of hit-and-miss to drilling for oil, technological advances in the study of seismic data and sophisticated computer modelling have taken some of the chance out of the process, but the only way to know for sure is to drill. The Ocean Endeavor is equipped to drill as far as 35,000 feet (the first 10,000 feet is water), or some 10 kilometres, down. Airliners typically fly at 35,000 feet.

On the Ocean Endeavor, 140 (mostly) men labour to keep the drilling going day and night. The engineers, mechanics, welders, geologists, drill assemblers, deck hands, divers, medics and cooks work 12-hour shifts on a two-weekson, two-weeks-off basis. Down to Business

Although no two holes, or wells as they are called, will take the same time to drill – it depends on the density of the rock and whether the hole is an exploratory well looking for new deposits of oil or a development well in an already proven oil field – the process is always the same.

Drilling both types of well involves sending a rotating length of pipe, known as the drill string, down through the water and into the ocean floor. At the business end of the drill string is the drill bit, a boring tool that cuts and smashes whatever it encounters. The drill bits, which get progressively smaller the deeper the well goes, usually include rotating teeth made from hardened steel, tungsten or even industrial diamonds. High-tech sensors and measuring equipment sit directly above the bit, sending images and data back to the rig.

Also key to the string are several extra-heavy (two-tonne or more) sections of pipe called drill collars that provide added weight and downwards pressure on the bit. The Ocean Endeavor’s general drill pipes, each weighing 550 kilograms, come in threaded sections 45-feet long which are assembled on deck two at a time before being added to the drill string through the towering structure at the centre of all oil rigs known as the derrick.

In all, nearly 800 pieces of drill pipe (worth US$4.5 million) need to be stacked on deck to drill a 35,000- foot well.

Also stored on deck are the riser joints. Larger in diameter than the drill pipe, the steel riser is assembled on deck and extends to the sea floor. It is put in place after the drill string first breaks through the seabed. The hollow riser lets drilling fluid, known as mud, flow between the rig and the sea floor.

This mud – a mixture of water, clay and chemical additives – is pumped from huge on-board mud pits through the drill string to cool, clean and lubricate the drill bit and help balance the enormous pressure that builds up that far down. The mud also sends the cuttings back up to the rig where the mixture is flowed to huge sieves called shakers. These shakers separate the cuttings from the mud, allowing the mud to be recycled and pumped back down the well. The Ocean Endeavor holds 13,300 barrels of mud, which is stored among its pontoon, legs and deck pits.

Despite the protection of the mud, drill bits wear out quickly and often break. Some diamond-tipped bits have a drilling life of up to 6,000 feet, but an average bit’s life is shorter. The only way to replace a worn bit is by pulling the whole drill string up, a time-intensive process. If the bit is found to be broken, a special bit will be sent down to smash or shove any loose pieces out of the way.

Five Year Mission

Day after day, night after night, the well is dug deep until oil is found. When, or if, the oil deposit is hit, the Ocean Endeavor’s work is nearly done because the job of a drilling rig is to locate oil, not extract it. Once the oil is found, the string and riser are hauled in and disassembled, leaving the cemented well, which is capped on the sea floor by a ‘Christmas Tree’, named because its assembly of fittings and valves resembles the festive decoration.

The Ocean Endeavor is then towed by tug to start drilling another well, remaining at sea for the full five years that regulations permit before it has to be docked for a critical check-up.