The Facts on Deepwater Drilling
Did you know that there has been more than 3,800 wells drilled offshore in Australian waters? And that approximately 150 wells* have been drilled in water depths greater than 1,000 meters? According to the International Energy Agency (IEA), deepwater has accounted for around half of discovered oil and gas resources over the last ten years.
Deepwater drilling is increasingly common around the world, including in the Norwegian Sea, the Gulf of Mexico and offshore Canada, Africa, India, South America and Australia.
So how does deepwater drilling work?
Step 1: Exploration
Energy companies use seismic survey vessels to explore large areas while trailing equipment that sends sound waves into the ocean floor. The sound waves then bounce off layers of rock beneath the seafloor and are picked up by sensors or “geophones” attached to the survey boat. (Learn more about marine seismic surveys)
Geologists can then analyse this data to determine if hydrocarbons may be present. Offshore they generally occur in porous sandstone layers, where the resource is trapped in the pores of the rock.
Step 2: Installing a well casing and blowout preventer
For deepwater drilling, energy companies will use drill ships or semi-submersible floating rigs. These facilities are positioned using GPS technology and thrusters and are capable of extracting resources from water-depths ranging from 600 to more than 3,600 metres. The technology enables safe drilling even in high seas.
Once the initial hole is drilled (called the top-hole), a sturdy steel casing is inserted into the hole and firmly cemented in place to fill the gap between the rock and the steel tube’s outer wall.
A subsea wellhead is fitted and a blowout preventer is lowered into onto the well opening to effectively seal it. This is a large, specialised mechanical device that is equipped with hydraulic rams that can seal the bore if necessary. Drilling continues using progressively smaller diameter casings until they reach the target depth.
Step 3: Drilling and well completion
Should a resource be found the well may be a “producing well” which allows oil or natural gas to flow through the casings and ‘up’ to the receiving platform in a highly controlled manner. Typically, this casing is only about 20cm wide.
After a production or exploration operation is finished the well is permanently sealed.
- There are approximately 90 wells drilled offshore Australia every year.
- Australia has been exploring beneath deep waters for over 40 years.
- The International Energy Agency defines “deepwater” as a water depth greater than 400 meters.
- The first deepwater well in the world was drilled in 1975, and the first ultra-deepwater well (greater than 1,500 meters) was drilled in 1986.
- Today, at least 3 billion barrels per day are produced from deepwater/ultra deepwater operations.
- Current record for deepest water depth for an offshore oil rig is approximately 3,400 metres under water.
- For comparison, Exxon’s newly-approved offshore well in Victoria is only about 2,300 meters under water.
- The well Equinor proposes to drill in the Great Australian Bight next year is located in a water depth of 2,239 metres.