How does offshore drilling work

We consume more than 80 million barrels of the stuff every day [source: CIA]. To meet our ravenous demand for fossil fuels, petroleum companies constantly comb the planet for new reserves. Since oceans cover nearly three-quarters of Earth's surface, a great deal of those reserves wind up underwater. After all, drilling on land is an undertaking on its own.

And how do you do all of this, with tons of special equipment, in the middle of rough seas? To surmount these obstacles, petroleum companies have invested billions into the development of offshore drilling and offshore oil platforms. The first of these platforms was constructed in at the end of a wharf in California. In the years to follow, oil prospectors pushed out into the ocean, first on piers and then on artificial islands.

In , a Texan oilman unveiled the first mobile oil platform for drilling in wetlands. The structure was little more than a barge with a drilling outfit mounted on top, but it set the example for decades of advancements to come. In the years that followed, petroleum companies moved even farther into the ocean. In , a consortium of oil companies built the first platform that you couldn't see from land in the Gulf of Mexico. Even the North Sea, which endures nearly constant inclement weather, is currently home to many offshore drilling sites [source: The Guardian ].

Today's oil rigs are truly gigantic structures. Some are basically floating cities, employing and housing hundreds of people. Other massive production facilities sit atop undersea towers that descend as far as 4, feet 1, meters into the depths -- taller than the world's most ambitious skyscrapers. In an effort to sustain their fossil fuel dependency, humans have built some of the largest floating structures on Earth.

In this article, we'll examine how petroleum companies go about sniffing out this buried, black gold and the methods they use to extract it. Spanish conquistadors observed oil rising to the surface in the Gulf of Mexico in the 16th century, and the Chinese drilled for it in the ground as early as A. To find even older evidence, you don't have to look any farther than the prehistoric animals unlucky enough to have been consumed by the world's tar pits.

All of this oil began as tiny plants and animals called plankton , which died in the ancient seas between 10 and million years ago. This decaying matter drifted to the bottom of the ocean and, over time, was covered with sand and mud. In this oxygen-free environment, a kind of slow cooking process took place. Millions of years of heat and pressure eventually transformed this organic material into vast deposits of liquid, gas and solid petroleum, all capped in traps under thick layers of rock.

We call liquid petroleum oil and gaseous petroleum natural gas. Solid petroleum deposits often take the form of oil shale or tar sands. Needless to say, these fossil fuel deposits don't just start bubbling crude every time a hillbilly fires a rifle. Geologists study surface features and satellite maps, check soil and rock samples, and even use a device called a gravity meter to find subtle gravitational fluctuations that might indicate a subterranean flow of oil.

Not all of these options are particularly viable, however, if the terrain you're canvassing is thousands of feet below pitching ocean waves. When searching for fossil fuels at sea, oil geologists are able to use special sniffer equipment to detect traces of natural gas in seawater. But as this method can only help find seeping deposits, oil companies largely depend on two other means of locating traps. When close to the surface, certain rocks affect the Earth's normal magnetic field.

By using sensitive magnetic survey equipment, a ship can pass over an area and map any magnetic anomalies that occur. These readings allow geologists to hunt for the telltale signs of underground traps.

Surveyors can also detect possible traps through the use of seismic surveying. This method, known as sparking , involves sending shock waves down through the water and into the ocean floor. Sound travels at different speeds through different types of rock. If the shock wave reaches a change in rock layers, it bounces back up toward hydrophones dragged behind the survey ship. With the aid of computers, seismologists can then analyze the information to pinpoint possible traps in the Earth.

Of these two methods, air guns are far less of a threat to sea life, but even acoustic pollution poses a threat to such seismically aware sea animals as the endangered blue whale.

Well, it's time to mark down the GPS coordinates, plant a buoy and obtain a government lease to begin a little exploratory drilling and see what you've got. Once oil companies have identified a possible undersea oil deposit, they have to obtain drilling rights. Most of the coast and ocean belong to states or nations, so companies have to lease desired areas from the respective government.

For more information about this issue, read Who owns the oceans? You can send shock waves down to the ocean floor all day, but ultimately you're going to have to drill a little if you want to know if you have a potential gusher on your hands. To handle this job, oil companies send out a mobile drilling platform to perform exploratory drilling on a site. Some of these platforms are ship-based, but others have to be towed to the drilling site by other seagoing vessels.

Geologists initially drill to obtain a core sample. The principle is the same as if you stuck a hollow cylinder into a birthday cake and then removed it. You'd then be able to examine the cylinder to discover what varying layers of icing and cake existed inside the cake.

Will there be ice cream? This is one method of finding out without cutting yourself a whole slice. Of course, oil geologists aren't hoping for ice cream. They're looking for signs of petroleum, which they call a show. Once a show has occurred, drilling stops and geologists perform additional tests to make sure oil quality and quantity are sufficient to justify further action.

If so, they then drill additional wells to substantiate the findings. Once geologists have established the worth of a petroleum deposit, it's time to drill a production well and begin harvesting the riches.

An average well lasts a good 10 to 20 years before it's no longer profitable, so offshore production platforms are built with a long stay in mind. The platforms are typically fixed directly to the ocean floor using either metal and concrete foundations or tethering cables. As you might imagine, the platform has to remain as stationary as possible during all this drilling, no matter how severe the weather becomes.

One platform can boast as many as 80 wells, though not all of them go straight down. Directional drilling allows oil platforms to sink production wells into the ocean floor at an angle in order to reach deposits miles away from the drill site. If you've seen the film "There Will Be Blood ," then you may know this as the "I drink your milkshake!

In the film, a maniacal, mustached oilman boasts that, through directional drilling, he's managed to drain all the oil beneath a nearby parcel of land. This issue also arises in the offshore drilling industry. Even after its wells have run dry, offshore production platforms often find renewed life as a central hub for other nearby oil platforms.

Now it's time to get busy drinking that offshore milkshake. You've established your multimillion- dollar offshore drilling platform and, miles beneath you, there's a fortune in untapped petroleum deposits.

The challenge in undersea drilling is transferring all that precious oil and gas from point A to point B without losing it and polluting the ocean. How do you tunnel into the Earth without water flowing into the hole or all the oil surging up into the sea?

To ensure accurate drilling, engineers connect the drill site to the platform with a subsea drilling template. On a very basic level, this serves the same purpose as the templates you might have used to trace a pattern or carve a jack-o-lantern design into a pumpkin. While the design may vary depending on the exact ocean floor conditions, the drilling template basically resembles a large metal box with holes in it to mark the site of each production well. Since production wells often have to sink miles into the Earth's crust, the drill itself consists mostly of multiple foot 9.

They're much like tent poles in this respect. A turntable on the platform rotates the drill string and, at the other end, a drill bit grinds through the Earth. The drill bit generally consists of either a rotating bit embedded with industrial diamonds or a trio of rotating, interlocking bits with steel teeth.

In the weeks or months it takes to reach the oil deposit, the bit may dull and require replacement. Between the platform and the ocean floor, all of this equipment descends through a flexible tube called a marine riser. As the boring hole descends deeper into the ground, operators send a constant flow of drilling mud down to the drill bit, which then flows back up to the platform. This thick, viscous fluid consists of clay, water, barite and a mixture of special chemicals.

The drilling mud lubricates the drill bit, seals the wall of the well and controls pressure inside the well. Also, as the drill bit shreds rock, the resulting fragments become suspended in the mud and leave the well in the rising, return flow. On the surface, a circulation system filters the mud before sending it back down the well.

The drilling mud acts as the first line of defense against high, subterranean pressures, but there's still a high risk of a blowout of fluid from the well. To handle these events, petroleum companies install a blowout prevention system BOP on the seafloor. If pressurized oil and gas gush up the well, the BOP will seal the well with hydraulic valves and rams.

Offshore drilling is the process of extracting petroleum from reserves located beneath the Earth's oceans instead of reserves located on the mainland. Offshore oil rigs have developed greatly over the past years, and have become gigantic structures that house hundreds of people at a time. Some facilities sit on towers that go to depths of meters below the surface, larger than any skyscraper ever conceived of. Recently, offshore drilling has increased in popularity as a result of the large amount of oil and other petroleum products used worldwide each day.

The IEA estimates that in the worldwide consumption of oil and liquid fuels will be 96 million barrels per day - working out to over 35 billion barrels a year. The process of drilling for oil and natural gas underseas is much more challenging than drilling on land.

Extraction, transportation, and environmental protection are all comparatively more difficult with offshore drilling than with traditional wells. In an attempt to make this process more simple, petroleum companies have developed offshore oil platforms to aid in this extraction. Once the offshore drilling platform is built, some method of extracting the oil and gas from beneath the ocean and moving it to the surface without losing it must be developed.

To drill without water flowing into the hole or having all the oil surge up into the ocean, a subsea drilling template is used. This template is simply a large metal box with holes in it that is used to guide the drilling process and marks the site of each production well. Once the locations of the drilling sites are marked with this template, the drilling process can begin.

To drill these wells, a number of 9 meter drill pipes are connected to form a large drill string used to reach deep into the Earth's crust. This drilling process can take a long period of time, lasting anywhere from weeks to months.

As the borehole moves deeper into the ground, a stream of drilling mud is sent to the drill bit, and then moves back up to the platform. For assignments in the US Gulf of Mexico, crews typically work a rotational schedule consisting of 21 consecutive days aboard the rig followed by 21 days off. In international locations, our crews typically work a rotational schedule of 28 days on and 28 days off. In a broad sense, operators drill two basic types of wells-exploratory to find new oil or gas deposits and development to prepare the discovery for production.

Water depths range from 20 to feet for jack-up rigs to up to 12, feet for semisubmersibles and drillships. Before drilling an exploratory well, an operator will conduct geologic surveys of an area to determine the potential for oil or gas deposits and to identify specific targets.

The operator then hires a drilling contractor like Diamond Offshore to drill exploratory "wildcat" wells offshore. The oil company chooses the location and supervises the operation, which may take as little as 15 days or as long as 12 months, of round-the-clock, seven-days-per-week operation to drill a single well depending on the complexity of the project.

Offshore rigs are designed for efficiency in living and working, with emphasis on keeping the rig steady in gulf or ocean waters. See rig basics. Offshore wells are drilled in much the same way as their onshore counterparts-with several allowances for the offshore environment.

A conduit made from lengths of steel pipe permits drilling fluids to move between the rig-at the water's surface-and the sea floor.