Drillships, the next generation
Offshore drilling has been transformed since it started 100 years ago. Once workers on wooden platforms used hoisting equipment and brute strength to operate drilling rigs; now engineers seated on a hi-tech ship use a joystick and state-of-the-art monitors. The latest ship designs combine ever-deeper drilling with increased fuel efficiency.
Over 200km (130 miles) off the south-east coast of Louisiana, USA, a helicopter touches down on a helipad on the bow of a ship. Its passengers trade places with a team of workers waiting close by. This is changeover time for the crew of Bully I, a drillship working on the Mars B deep-water project in the Gulf of Mexico.
Shrinking to drill deeper
Traditionally the extra equipment, pipes and well lining needed to reach deep-water oil and gas resources at greater depths pushed up the size of drillships. Bigger ships require more fuel.
But Dave Loeb, Shell Wells Operations Manager, wanted a more economic solution. In 2005, Shell and offshore drilling contractor Noble Corporation worked on a new design that eliminates surplus space and carries only essential equipment. The result is the Bully.
Around 160 crew members rotate on 21-day shifts to manage operations on board Bully I. The ship is designed for deep-water operations and can drill in water depths up to 2,500 metres (8,500 feet).
Two sister ships were built. Bully I has drilled wells at the Mars B project in the Gulf of Mexico, while Bully II is helping expand the Parque das Conchas project off Brazil.
“The Bully is dwarfed by some of the larger drillships,” says Dave. “But it still does a very good job.”
On-board crew facilities resemble those of a hotel, with a gym, cinema and quality catering that even includes a pastry chef.
The Bully needs a base onshore to replenish supplies and equipment more often. In more remote locations, larger drillships are still used.
The Bully compared to a conventional drillship
- Around 2.5 metres (eight feet) narrower.
- Up to 80 metres (260 feet) shorter.
- Thrusters that keep the ship’s position combined with a smaller hull and electronic engine controls help improve fuel economy. It uses up to 26,000 litres (7,000 fewer gallons) of fuel a day on average compared to other deep water drillships.
- A compact, box-type drilling tower takes up less space than a conventional drill tower design and contains all hoisting equipment inside, keeping people safer.
- The drill tower is equipped with hoists that allow the crew to drill on one side while conducting other drilling-related operations on the other.
- Automated technology replaces a lot of manual work, lowering costs and increasing on-board safety.
- Can operate in water as shallow as 45 metres (150 feet) with the correct mooring.
- It can drill down to 12,000 metres (40,000 feet).
With a desire to take the new generation of drillships still further, drilling-tower design firm Huisman took another approach.
“For the new drillship we first designed the drilling package then designed the vessel around it,” says Olaf van der Meij, Huisman Senior Concept Engineer.
On conventional drillships, the drilling and well-lining operations take place within the derrick structure. The new design places the drilling and well-lining equipment outside the tower structure. Thanks to the hoists on either side of the tower, the two processes can happen simultaneously. This boosts productivity and improves safety.
In addition, the drilling floor can be hoisted up to deploy the blow-out preventer, a mechanical device designed to rapidly seal off the well if control is lost. Without the need for a raised drill floor, the ship’s centre of gravity is lowered for greater stability.
Shell and Noble commissioned two of these new vessels in 2012 and 2013. The Globetrotter has been drilling for Shell in the Gulf of Mexico since 2012.
Watch how a deep water well is drilled
Title: Drilling 101 – How a deep water well is drilled – from YouTube
Duration: 5:31 minutes
A visual and audio description of the process of creating a deep water well.
The video uses computer generated imagery to illustrate the tools, equipment and processes described by the narrator to give a simple overview of the process of drilling a deep water oil or gas well.
Drilling 101 – How a deep water well is drilled Transcript
[Background music plays]
Slow, solemn music.
Deep water drill in calm seas.
Computer animation of a deep water well in the ocean.
Shell Deep Water. Drilling 101
Shell Deep Water is fueling the growth of upstream Americas by safely developing new reserves and maximizing the potential of its existing producing assets in the Gulf of Mexico, Brazil, and Venezuela.
Gulf of Mexico. Brazil. Venezuela against a background of sea surface.
Drilling a safe deep water well can take years of planning and preparation. After identifying potential oil and natural gas reservoirs beneath the sea floor using seismic technology a drill site is selected. Shell geoscientists choose the drill site location on the sea floor based upon the safest well path that will encounter the targeted oil and natural gas. For an exploratory well in water depths up to 9000 feet deep this sea floor location is generally directly above the reservoir.
Shot of deep water drill at sea. Shot rotates to give a 360 degree view.
Ascending numbers ending at 9000 ft. below sea level. Oil and natural gas reservoir.
Shot showing different layers.
9000 FT below sea level.
A drilling rig is required to drill a well. In deep water the rig may be on one of three vessels, a drill ship, a semi-submersible vessel, or it may be part of a floating production platform. All rigs have a hoisting system to raise and lower the drill pipe and tools needed to drill the well, a blowout preventer, or BOP stack, and a pumping system to circulate fluids in and out of the well while drilling. It’s time to drill the hole, or well bore, using a drill bit. This initial step is called spudding in the well. The shallow sediments just below the sea floor are often very soft and loose; to keep the well from caving in and carry the weight of the well head a large diameter base pipe, or casing, is drilled or jetted into place. The base pipe is assembled at the rig floor and a drill bit connected to a drill pipe is run through the inside to the bottom of the casing. The entire assembly is lowered to the sea floor by the rig hoist. At the sea floor the driller spuds the assembly into the sea floor sediments then turns on the pump. Water or a drill fluid is used to jet the pipe into place until the well head is just above the sea floor. With the base pipe and well head at the right depth the driller will release the bit and drill string from the jet pipe and drill ahead. While the well bore is being drilled mud is pumped from the surface down through the inside of the drill pipe. The mud passes through the jets in the drill bit and travels back to the sea floor through the space between the drill bit and the walls of the hole.
Overhead shot of drilling rig.
Computer generated shot of drill ship, a semisubmersible vessel and a floating production platform surrounded by calm seas. Computer generated shot showing a hoisting system. Diagram of BOP stack. Shot changes to show pumping system. Drill is shown being lowered. Diagram showing layers of sediment below the sea floor. Large pipe or casing is shown being lowered. Diagram of drill with drill bit inside the casing. The assembly is shown being lowered to the sea floor by the hoist. Shot of drill drilling through the sea floor. Water is spraying around the pipe. Drill is shown through several layers. Mud is shown being pumped down from the surface inside the drill pipe.
Lift rock cuttings from well bore. Keep the drill bit cool & lubricated. Fill the well bore with fluid to equalize pressure and prevent other fluids from flowing into the well bore.
Diagram showing rock cuttings floating. Large blue coloured machine. Fluids show through transparent panels. Computer generated diagram showing how the drill pipe is permanently connected to sea floor.
Drilling mud is used to 1, lift rock cuttings from the hole. 2, keep the drill bit cool and lubricated. And 3, fill the well bore with fluid to equalize pressure and prevent water or other fluids and underground formations from flowing into the well bore during drilling. The mud is an environmentally friendly water-based mixture of clay for thickness and fine ground rock, or barite, for weight. At the planned depth the driller will stop drilling and pull the bit out of the hole. A smaller pipe or casing string is then screwed together, connected to the drill pipe, and run down to the sea floor and into the well. To permanently secure the casing in place, cement followed by mud is then pumped down the inside of the drill pipe. To separate the cement from the mud a cementing plug is used. The plug is pushed by the mud to ensure the cement is placed outside of the casing, filling the annular space between the casing and the open hole wall. On some locations a second surface casing is needed, thus the well is drilled even deeper. In the second surface casing interval the well is cemented using a second smaller casing string, repeating the same process used in the last hole section.
At this point in the well the pressure in the deeper rock may be too high to continue with the simple water-based clay mud, or there may be the potential to encounter oil or gas. Before drilling below this point a blowout preventer with a riser will be installed at the sea floor. The BOP stack is a massive system of valves and rams that protect the rig and environment from oil and gas flows should the weight of the drilling mud be too low. The BOP stack is connected to a pipe called a riser. The riser connects the rig to the well and allows us to circulate the drilling fluid and rock cuttings all the way back to the rig on the surface. The BOP stack is fully tested before we drill further. Drilling now resumes with the drill bit and drill pipe always operating through the BOP stack. Just as we did further up the hole casing strings are run and cemented in place when needed to cover up the open hole sections. When the oil and gas zones targeted by the geologists are reached and the presence of an oil or gas zone is proven a final casing string may be installed if the sea floor location is favourable for future development. This final casing string allows for the future safe production of the oil and natural gas.
Diagram of yellow BOP stack. The BOP stack is connected to a black pipe which rises to the surface. Computer generated diagram showing the full process.
Deep water well in calm seas.
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