Deep Water Drilling Vs. Shallow Water Drilling

Written by john brennan
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Deep Water Drilling Vs. Shallow Water Drilling
Offshore drilling has become an important contributor to world oil supply. (Jupiterimages/liquidlibrary/Getty Images)

Offshore drilling is a difficult endeavour, but one that has become increasingly important to world oil supply. Deepwater drilling must overcome more technical challenges than shallow-water drilling, because much greater ocean depths are involved. Both types of offshore drilling entail some risk of a spill. They share many similarities but also exhibit important differences.

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Depth

The federal government defines deepwater drilling as drilling that takes place at depths of 500 feet or more -- sometimes at depths as great as 12,000 feet, miles below the ocean's surface. Shallow-water drilling has depths less than 500 feet. The base of a shallow-water drilling platform can be accessed by divers if repairs are needed. The seabed is so far below a deepwater platform, however, that divers cannot access the wellhead where the drill bores into the seabed. Submersibles must be used if repairs are needed.

Platforms

Whether shallow or deep, drills for oil extraction must be mounted on a drilling platform. Down to about 1,500 feet, you can fix the platform to the seafloor with rigid metal or concrete legs. At depths up to 3,000 feet, companies may use compliant towers, which are similar but more flexible. Down to 6,000 to 7,000 feet, you can use a floating drilling platform or a tension leg system, which features long, hollow flexible legs that connect the platform to the seabed and allow for side-to-side motion. Spar-type platforms in even deeper waters have a large cylinder beneath the platform. The cylinder doesn't reach the seabed but is tethered to it by giant cables.

Problems

Deepwater drilling is much more expensive than shallow-water drilling. The platforms are technically more challenging to construct. Only the rising price of oil has made it profitable for companies to invest in these kinds of ventures. Declining revenue from shallow-water and onshore sources has driven many companies to seek oil in deeper and deeper waters despite the cost of operation.

Safety

Both shallow-water drilling and deepwater drilling carry the potential for spills during oil production or transportation. The 2010 Deepwater Horizon disaster in the Gulf of Mexico made many Americans more conscious of these risks. In general, deepwater drilling is somewhat riskier than shallow-water drilling, because the pressures and depths involved are greater. As the Deepwater Horizon case demonstrated, it's more difficult to access the blowout preventer and well for repairs if something goes wrong on a deepwater well. Given the demand for oil and its increasing scarcity, deepwater drilling may become more important in the future.

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