Offshore Drilling
Not all oil deposits are on land, some are found in deep waters under the ocean floor.
Using sonic equipment, the oil companies determine the drilling sites that will most likely produce oil. Then they use a mobile offshore drilling unit (MODU) to dig the initial well. There are four main types of MODUs:
A MODU’s job is to drill down into the ocean’s floor to find oil deposits. The part of the drill that extends below the deck and through the water is called a riser. The riser allows for drilling fluids to move between the floor and the rig. Engineers lower a drill string
– a series of pipes designed to drill down to the oil deposit – through the riser.
At the sea floor is the blowout preventer (BOP). The blowout preventer has a pair of hydraulically powered clamps that close off the pipe leading up to the rig in case of a blowout. As the rig drills down deeper, the crew add more pipes to the drill string. Each section of the drill pipe is 9.1 metres long.
To add stability to the well, metals casings are used, like on land based oil rigs to prevent the well from collapsing in on itself. Each casing is lined with cement, the casings get narrower as the well gets deeper. Oil companies use smaller and smaller drill bits as the well gets deeper. At each annulus – the spot where a narrower casing joins with a wider one – engineers use a liner hanger O-ring to seal the two sections together.
When oil is found in the MODU, the engineers seal off the well with a pair of plugs to prepare for a production rig. The bottom plug sits near the oil deposit, the drillng mud or seawater provide the pressure for the plug to stay in place. The engineers place the top plug to tap the oil well.
Using sonic equipment, the oil companies determine the drilling sites that will most likely produce oil. Then they use a mobile offshore drilling unit (MODU) to dig the initial well. There are four main types of MODUs:
- A submersible is aMODU which usually consists of a barge that rests on the sea floor at depth of 30-35 feet (9.1 to 10.7 metres). On the barge’s deck, there are steel posts that extend above the water line. A drilling platform rests on top of the steel posts, these type of rigs are used in calm waters
- A jackup is a rig that sits on a floating barge. A ship tows the barge to the drilling site. The jackup can extend legs down to the sea floor once positioned. Once each leg is secured, the jackup continues to ratchet the legs so that the platform rises above the water level. This keeps the rigs safe from waves and tidal motions. Jackups can operate in depth of 525 feet (160 metres)
- Drill ships are ships that have a drilling rig at the top deck. The drill operated through a hole in the hull. Drill ships are very manoeuvrable and can be used in deep waters.
- Semisubmersibles float on the surface of the ocean on top of huge submerged pontoons. Some have propulsion systems, which allow them to move to the drill site while others have to be towed in position. Anchors are used to maintain the structure’s position and computers control the tension of the chain of the anchors to adapt for drift.
A MODU’s job is to drill down into the ocean’s floor to find oil deposits. The part of the drill that extends below the deck and through the water is called a riser. The riser allows for drilling fluids to move between the floor and the rig. Engineers lower a drill string
– a series of pipes designed to drill down to the oil deposit – through the riser.
At the sea floor is the blowout preventer (BOP). The blowout preventer has a pair of hydraulically powered clamps that close off the pipe leading up to the rig in case of a blowout. As the rig drills down deeper, the crew add more pipes to the drill string. Each section of the drill pipe is 9.1 metres long.
To add stability to the well, metals casings are used, like on land based oil rigs to prevent the well from collapsing in on itself. Each casing is lined with cement, the casings get narrower as the well gets deeper. Oil companies use smaller and smaller drill bits as the well gets deeper. At each annulus – the spot where a narrower casing joins with a wider one – engineers use a liner hanger O-ring to seal the two sections together.
When oil is found in the MODU, the engineers seal off the well with a pair of plugs to prepare for a production rig. The bottom plug sits near the oil deposit, the drillng mud or seawater provide the pressure for the plug to stay in place. The engineers place the top plug to tap the oil well.