The Deepwater Horizon drilling rig which caught fire few days back, lasted two days, then sank in 5,000 ft of water in the Gulf of Mexico. The rig belongs to Transocean. The rig was originally contracted through the year 2013 to BP and was working on BP’s Macondo exploration well when the fire broke out. The day rate for the rig costs about US$500K per day to contract. The complete drilling day cost, with helicopters and support vessels and other services, will cost closer to US$1 mil per day to operate drilling for oil and gas. The rig building cost about US$350 mil in 2001 and would probably double that if order one today with steel prices, material cost rising. The rig represents the cutting edge of drilling technology. It is a floating rig, capable of working in up to 3000m water depth. The rig is not moored as it would be too costly and too heavy to suspend this mooring load from the floating structure. There should be a cost study done to compare options of moored or DP and long term operational cost viability. This rig has a triple-redundant computer system uses satellite positioning to control powerful thrusters that keep the rig on station at all times. From web information, seems like the rig had apparently just finished cementing steel casing in place at depths exceeding 18,000 ft. The next operation was to suspend the well so that the rig could move to its next drilling location, the idea being that a rig would return to this well later in order to complete the work necessary to bring the well into production. Initial speculation news that was thought that somehow formation fluids –oil /gas –got into the wellbore and were undetected until it was too late to take action. Usually a “kick” would have been detected from the cabin monitoring controls. With a floating drilling semi-submersible, because it moves with the waves, currents and wind, the main pressure control equipment sits on the sub-seabed –the bottom point in the well is only part unmoved. There is a setup of ‘BOP’s” and controlled with redundant systems from the rig being laid just above the seabed. In the event of a serious emergency, this BOP tree will be shut and close against the well preventing back flow of the gas from seabed. Investigation will take some months before all of the reasons are known. The well still is apparently flowing oil, which is appearing at the surface as a slick. They have been working with remotely operated vehicles, or ROV’swhich are essentially tethered miniature submarines with manipulator arms and other equipment that can perform work underwater while the operator sits on a vessel. They have been trying to close the well in using a specialized port on the BOP and a pumping arrangement on their ROV’s. Seems to be unsuccessful so far. Specialized pollution control vessels have been scrambled to start working the spill, skimming the oil up. In the coming weeks there is another plan to move in one other rig ( could be from DD3 built by us ) to drill a fresh well that will intersect the blowing one at its pay zone. They will use technology that is capable of drilling from a floating rig, over 3 miles deep to an exact specific point in the earth –with a target radius of just a few feet plus or minus. Once they intersect their target, a heavy fluid will be pumped that exceeds the formation’s pressure, thus causing the flow to cease and rendering the well safe. Probably will take months to get this done, bringing all available offshore drilling technology to fruition. It will soon be an ecological and environment hazard if the well flows continuously and not stopped.
Subsea systems challenges :
Other challenges facing the rig operator of this kind of deep water drilling vessel relating to deepwater depth in several ways:
•The temperature at the seafloor is such that hydrate formation in any gas migrating to the BOP can freeze the system closed. Provision must be made to flush the connectors routinely with BOP operating fluid (which contains glycol) or as a last resort to inject methanol remotely from the ROV.
•The well pressure at approx 7,500 feet is 230 bar or 3,333 psi. All of the subsea BOP equipment must work in cold, dark, high pressure environment around one and a half miles from the vessel drill floor.
•The long column of drilling fluid in the riser exerts a pressure on the formation. In shallow water this pressure is usually far enough from the fracture pressure of the formation that cuttings can be transported out of the hole without exceeding the fracture pressure and invading the formation. This allows longer sections of hole to be drilled before second casing. As water depth increases the difficulty of keeping mud weights between fracture gradient and pore pressure causes an effective well design to include multiple casing strings driving up both the complexity and the cost of the well
•The marine riser itself must be strong enough to support choke and kill lines, boost lines, hydraulic lines, dual gradient lines and MUX cables and yet light enough to allow a combination of top tension and buoyancy to support it for a defined range of mud weights and vessel offsets.
•The time to run any piece of equipment to the seafloor is a significant part of the total operational time. It can take days to round trip the BOP in 7,500 feet of water and the rig is vulnerable to environmental extremes while the BOP is suspended below the rig
Below typical schematic of the subsea BOP control system which should be able to shut the well once activated. With so many cables and tubings going down the seabed, probably anything can go wrong during the Horizon emergency and Murphy's law set in, anything wrong goes.
As a result, the design of the riser, its buoyancy, the BOP and sub-sea system is the most critical element of the overall design of the rig. The size and weight of a 21” riser and 18 ¾” 15K BOP system that dictates the overall size and therefore cost of the rig. Most deepwater operators are well aware of this and extensive research has been undertaken by them to find ways to allow smaller and less capable rigs to drill safely and effectively in the ultra deep water. These technologies include :-
•Dual density drilling – to solve the pressure differential problem referred to above.
•Slimbore wells to allow the use of 16” riser and a 13 5/8” BOP
•Expandable tubing to facilitate slim bore wells
•Free standing riser systems
•Artificially buoyant seabeds bringing the wellhead closer to the surface
All of these technologies hold future promise but they also represent compromises in the primary objective which is to deliver a quality high production well to the operator.
With the Horizon rig going “under”, oil began gushing to the surface at an ever-increasing rate. In the worst case scenario, the daily outflow of oil is projected to reach as many as 60,000 barrels (2.5 million gallons) per day.
Some methods have been used for cleaning up the Gulf of Mexico, Louisiana coastline mess, both through working beneath the waves at 5,000 feet and atop, as the oil surfaced :-
It was a bad luck that the BOP failed to activate. Other semi-submersible have been deployed to try to fix the device with help of ROVs ( remote operated vehicle ) or install a new BOP to stop the flow of oil at its lowest point, but have failed so far. It is not simple task to do it at deepsea where controls underwater are not easy with the temperature and current beneath.
However, the effort to place a massive containment dome over a gushing underwater wellhead in the Gulf of Mexico was dealt a setback when a large volume of hydrates -- icelike crystals formed when gas combines with water -- accumulated inside the vessel, The dome was moved off to the side of the wellhead and is resting on the seabed while crews work to overcome the challenge
Oil skimmers — Since some oil sits on top of the water, a clever skimming system can separate the oil to be siphoned away (and potentially even sold on the market like normal oil). Skimming devices can range from small to massive, but despite advances in the technology, none are large enough to deal with a Gulf-sized spill, at least without months of work.
Fire — One of the oldest technologies at least for gasoline, will burn off quickly and even explode. But the “sweet crude” welling up is actually a thick, heavy substance that doesn’t always burn easily or evenly. The Coast Guard attempted to burn enough oil to prevent it from reaching the Louisiana coastline, but failed.
Reading & Bates Falcon RBS-8D
Port of registry: Majuro
Route: Gulf of Mexico
Ordered: December 1998
Builder: Hyundai Heavy Industries
Cost: US$560 million 
Acquired: February 23, 2001
Maiden voyage: Ulsan, South Korea – Freeport, Texas
Out of service: April 21, 2010 (exploded)
Identification: ABS class no.: 0139290
Call sign: V7HC9
IMO number 8764597
Class and type: ABS +A1 DPS-3 Column Stabilized MODU
Tonnage: 32,588 t (32,073 LT; 35,922 ST)
Displacement: 52,587 t (51,756 LT; 57,967 ST)
Length: 112 m (367 ft)
Beam: 78 m (256 ft)
Height: 97.4 m (320 ft)
Draught: 23 m (75 ft)
Depth: 41.5 m (136 ft)
Installed power: 42 MW
Main Power 6 x Wartsila 18V32 rated 9775 hp each, driving 6 x ABB AMG 0900xU10 7000 kW 11,000 volts AC generators
Emergency Power 1 x Caterpillar 3408 DITA driving 1 x Caterpillar SR4 370 kW 480 volts AC generator
Power Distribution 8 x ABB Sami-Megastar Thruster Drives, 5.5 MW and 6 x GE Drilling Drive Lineups 600 V 12 MW
Deck Cranes 2 x Liebherr, 150 ft boom, 80 mt @ 35 ft
Thrusters 8 x Kamewa rated 7375 hp each, fixed propeller, full 360 deg azimuth
Speed: 4 kts
Notes: 8202 tonne Variable Deck Load, DP Class 3, 8 thrusters, 10,000 ft drilling water depth
Video with courtesy of BP