The Deepwater Horizon incident at Macondo in the Gulf of Mexico that took place on April 20th, 2010, had a profound impact on the oil and gas industry. It was considered as the largest marine oil spill in the history of the petroleum industry, and the greatest environmental disaster in American history, with an estimated discharge of 210 million US gallons. The incident brought to light the necessity to take all measures possible to prevent the escape of petroleum in case of a blowout. Blowout preventer (BOP) is a device used to handle the uncontrolled release of crude oil or natural gas. It ensures well safety by working as a valve that closes the oil well when the drilling crew loses control of formation fluids. A BOP is critical to a drilling operation for the safety of the crew, drill rig, well integrity and for the safety of the surrounding environment. To ensure BOP’s do what they should in case of a blowout, the BOP’s need to be dependable, strong, well-maintained, and in proper working condition at all times.
What is a Blowout Preventer (BOP)?
A BOP is basically an assembly of safety valves that are designed to seal a well automatically in case of a blowout. While blowouts are rare, it is necessary to have measures in place to control the damage that can be caused otherwise. The BOP is installed in between the wellhead system and the drill floor before any drilling activities into the reservoir zone actually begin. The BOP is operated remotely from the rig or using a remotely operated vehicle (ROV). A single assembly of BOP can consist of six to eight individual blowout preventers stacked together. BOP was developed in the 1920s for oil and gas drilling and has been improved upon regularly. The Macondo incident has highlighted the need to make industry standards stringent for the operation and maintenance of BOP’s thereby ensuring the safety of the crew, rig and the environment.
Basic Components of a BOP
- Accumulator – This is the main control unit of a BOP that is activated by hydraulic pressure, and controls all interconnecting systems to prevent emergency situations. The accumulator is mounted on top of the BOP stack and provides power for other BOP units to run in case of system failure. The accumulator contains other features such as control valves, control manifold, pumps, hydraulic reservoirs, and compressed gas bottles.
- Pipe Ram – In case of a kick, this ram is activated and creates a seal between the wellbore and the outside of the drill string.
- Annular Preventer – This device can seal around any object in the wellbore, even upon itself by creating a seal with or without the drill string.
- Blind Shear Ram – Sometimes during a kick, it may be necessary to sacrifice the drill string to stop the flow of formation fluid inside the wellbore. The blind shear rams work by cutting or shearing the drill string and sealing the wellbore.
- Blind Ram – This device is used to seal a wellbore which has no drill string.
What does a BOP do in Case of a Blowout
Anytime the need arises to isolate the well at the seabed, the BOP system is activated. A closed BOP means that the well is “shut-in” or “sealed-off”. Other than for sealing off a well in case of a kick, BOP shut-in is also done as part of normal construction process for performing maintenance and pressure testing operations. A “kick” takes place when formation fluids flow into the wellbore migrating up past the BOP into the surface, known as loss of well control (LOWC).
As the well is being drilled, it is necessary to control the fluid pressure in the rock layers to prevent a kick. For this purpose, weighted drilling mud consisting of a mixture of water, barite, clay and non-toxic additives is used during drilling. The weighted column of mud creates downward pressure, preventing the movement of fluids trapped in the formation layers as the pressure created by the drilling mud is greater than the fluid pressure in the rock layers. Sometimes the fluid pressure in the rock layers may be greater than the pressure from the drilling mud, and hence, the mud column is closely monitored throughout the drilling operation as it will give the first indicator of a possible kick.
BOP isolates the wellbore by using two types of devices – annular preventers and ram preventers. The preventers are designed to withstand the maximum pressure that is expected in the wells.
- Annular preventers – This device has a rubber element that is designed to seal around most shapes and sizes of pipes. It is moved by a large hydraulic piston. When shut-in is required, one or more of the BOP’s is activated by a control panel. The BOP’s are operated using a high-pressure hydraulic fluid that is water-based making it environmentally safe. The pressurized fluids in the wellbore can be safely rerouted after the well is shut-in, through a system of pipes and valves on the BOP to specialized pressure-controlling equipment on the rig.
- Ram preventers – This device consists of two hydraulically activated rams placed opposite each other, designed to seal the well. A common BOP ram configuration for deep water is:
- Three pipe ram preventers capable of sealing off the well with the drill pipe inside the BOP.
- Two shear ram preventers that can cut different types of pipes with their two steel blades which when pushed together pinches and shears the pipe.
Maintenance and Upkeep of BOP’s
While BOP’s have been used worldwide to safely isolate wells with decades of proven field use, it is the regular maintenance and testing of the equipment that makes it reliable in the face of sudden blowouts. BOP systems are considered to be one of the most important pieces of equipment used in deep well drilling operations. Therefore, the inspection, testing, and quality control measures for a BOP should be carried out by experienced engineers prior to and during the duration of the drilling operation. Every person involved in handling and maintaining the BOP must undergo training and meet strict competency standards. Any indication from the BOP of a possible fault should be immediately attended to by suspending operations until required repairs are made. A properly functioning BOP can prevent environmental disasters and keep our estuaries, wetlands, and glaciers undisturbed while providing affordable oil and natural gas to millions of people worldwide.