Last updated November 15, 2019 at 3:28 pm
Following the Deepwater Horizon environmental disaster in 2010, new innovative technology was developed to avoid a similar situation from happening again.
Why This Matters: New technology could help prevent ecological disaster.
This article is sponsored by Bright-r.
On 20 April 2010, an explosion on board Deepwater Horizon, an oil rig in the Gulf of Mexico, started one of the most infamous environmental disasters of the 21st century. Eleven rig workers died and tens of thousands of animals suffered from the approximately four million barrels of oil which eventually spilled.
From the disaster came innovation, with new technology developed which would be capable of stemming a Deepwater Horizon-style spill early.
Preventing oil spills by blocking the flow
One of the main spill-prevention devices is the blowout preventer (BOP). Massive 15-metre-tall steel structures weighing up to 400 tons, BOPs are placed on the seafloor over the drill hole leading to the underground well. Should control devices within the well be overwhelmed and the oil or gas start to flow uncontrollably, the BOP clamps shut, physically blocking the pipe and preventing any flow.
To achieve this seal, modern BOPs generally have at least five ram preventers, and two additional annular preventers. As the name suggests, ram preventers consist of massive hydraulic rams that that push closed from each side of the hole, forming a tight seal around the drill that sits within the oil pipe. There are also ram preventers which, rather than forming a seal around the drill, cut straight through it much like a pair of garden shears. This second type of ram preventer then forms a seal without needing to rely on the drill itself.
The annular preventer is shaped more like a donut of rubber, which is driven into place by powerful hydraulic rams. The rubber ring is designed to seal around most sizes of drill, or close off a hole without a drill.
An annular preventer. Credit: Egmason/Wikimedia Commons
Following Deepwater Horizon these BOPs were given more preventers to increase redundancy after the investigation found the rig’s ram preventers had failed to form a seal. These changes also include extra shear-type preventers, which were also made more powerful to be able to slice through any obstructions. The maintenance and training requirements surrounding BOPs were also more highly regulated following the spill.
Capping stack is a last resort plug
The experience at Deepwater Horizon also showed, however, that a back-up to the BOP was required. The answer is the capping stack. Smaller than the BOP, they still weigh up to 100 tons, but are designed to be a last resort “plug” for an out-of-control well.
The first (and so far only) capping stack used was hurriedly developed during the Deepwater Horizon incident. Following the failure of the blowout preventer to stem the flow, well engineers used several established methods of attempting to control the leak, including a containment dome and funnelling the oil to other surface ships, all of which failed. Meanwhile, a group of engineers were building their new idea.
Firstly, the pipe and drill above the malfunctioning BOP were cut away, allowing unimpeded access to the leaking oil. Lowered into position from a surface ship, the capping stack eventually succeeded in blocking the flow where the other techniques failed.
Industry has invested heavily in new equipment in this space to make sure responses can be effectively deployed around the wellhead. For instance, the $25 million Subsea First Response Toolkit (SFRT) located in Jandakot in Western Australia can be immediately mobilised in the event of a loss-of-well control incident. The SFRT contains all the specialised equipment necessary to enable the wellhead and the surrounding area, including the seabed, to be cleaned up and made safe for the installation of a capping device, including a giant diamond saw in case debris needs to be cut away. Australia’s SFRT is one of just five worldwide.
A Blowout Preventer (left), capping stack (middle) and remote operated vehicle used to control the units. Credit: Equinor
Capping stacks have been developed rapidly
Since Deepwater Horizon, more capping stacks have been developed and the design improved further. Modern capping stacks have at least one shear ram for closing the well and shearing through obstructions, valves that can be opened and closed, as well as a secondary cap that can be installed on top of the capping stack itself.
To install on the out-of-control well, the capping stack is lowered from a surface ship working with remote-operated vehicles (ROVs) to guide it into place. With valves on the capping stack open, oil from the well streams into the bottom of the capping stack, through the system and out via the valves – this flow creates a Venturi effect that helps centre the capping stack above the oil source and makes it easier to position.
Once in place on top of the malfunctioning blowout preventer, an ROV manipulates the control panel on the side of the capping stack. The ram in the main hole is closed, and then valves are slowly closed which, much like a garden tap, cuts off the flow of oil. A further cap is then placed on the stack.
With the capping stack in place, drilling engineers are then able to drill a relief well and permanently block the flow. This relief well is a second well that intersects the original, and allows the engineers to pump cement or mud underneath the seafloor and block the flow.
The capping stack also features multiple spots where chemicals can be injected into the oil flow. These include chemical dispersants which help reduce the impact of the flowing oil and reduce the oil slick on the surface of the water. Other valves can also be used to divert escaping oil to surface ships using pipes.
Capping stacks held around the world
The operation of the capping stack by ROVs allows engineers to directly operate and monitor the stack safely and easily. After Deepwater Horizon, the availability and operation of these ROVs were also improved industry-wide.
Used as a last-resort should other intervention and containment strategies fail, there are 17 capping stacks being held around the world in strategic locations such as Singapore, Texas, Scotland and Africa, ready to be deployed in the case of a well blowout. If called upon the capping stack is prepared for transport either by sea or air to its destination. In most cases air transport requires the disassembly of the stack into 3 pieces, and then reassembly at the destination. However, a capping stack capable of being transported by air whole has also been developed, which requires the massive Antonov 124 aircraft to fly it to location.
The failures at Deepwater Horizon weren’t only technical, with other failings involved from human error to poor regulation. Similarly, the solutions developed extended beyond just a purely technological solution. In response to the tragedy, regulation, training and equipment availability was improved to reduce the likelihood of a similar occurrence. But should a similar incident happen again, the technological advancements mean wells can potentially be capped faster, minimising the oil spill and resulting in less destruction to the environment.
