A blowout preventer manufacturer or BOP is a large specialized unit weighing up to 400 tonnes to prevent an oil spill from occurring. It works sort of a valve to shut an oiler, almost like a plumber closing a valve during a pipe, and are proven to be highly effective in ensuring good safety.
The BOP is located at the top of the well near the seabed and surrounds the pipe or drill string, which passes through it. The fact that the BOP surrounds the pipe and stays in place throughout the drilling operation means that it can be used to shut in or seal off the well.
The BOP is deployed from the rig and installed on the well during the early stages of good construction. It remains during exploration activities, serving as a mechanical barrier which will be activated to seal off the well and isolate it from the rig or sea. Once activities on the well are complete, the BOP is retrieved back to the rig to be used for the next well.
The BOP can shut in the well in minutes. In all, the BOP has six independent shut-in mechanisms.
When is a BOP Operated?
When the BOP is closed, the well is said to be ‘shut-in’ or ‘sealed off.’ As part of the normal well construction process, it is necessary to shut in the well to perform routine operations such as pressure testing. A well may also be shut in for non-routine events, such as a ‘kick.’ A kick is a flow of fluid from the rock layers into the wellbore.
If no action was taken, these fluids could migrate up the well, past the BOP, and escape to the surface, in what’s referred to as a loss of well control. The present fluid pressure within the rock layers must be controlled because the well is drilled to stop oil, gas, and/or water entering the wellbore.
To achieve this, the opening is kept filled with weighted drilling ‘mud’ while it’s being drilled. This column of mud creates a downward pressure that prevents the inward movement of any fluids trapped in the rock layers into the wellbore. The pressure created by the mud is greater than the pressure in the rock layers.
This column of mud is monitored at all times and provides the first indication of a possible kick. This could occur if the fluid pressure in the rock layers is greater than the pressure produced by the column of drilling mud. Rig crews are trained to spot-kicks and follow rig specific procedures to isolate the well if they occur. Regular kick drills reinforce this training on the rig.
How does BOP work?
BOPs isolate the wellbore using two sorts of closure devices — ram preventers and annular preventers. For Equinor’s activities in the Bight, the BOP will have a minimum of five sets of ram preventers and two sets of annular preventers. Each set of preventers is designed to withstand the maximum expected pressure in the wells.
As such, only one set of preventers is typically required to isolate the well from the surface. Ram preventers consist of two hydraulically activated ‘rams’ positioned opposite each other and designed to seal off a well.
A common BOP RAM configuration for deepwater is:
› Three pipe ram preventers that can seal the well when drill pipe is inside the BOP. The pipe rams have opposing half-moon sections that allow a rubber seal to be made around the pipe.
› Two shear ram preventers capable of cutting a good range of pipe. Two steel blades are pushed together, pinching the pipe in the middle.
Annular preventers have a doughnut-shaped rubber element that is moved by a large hydraulic piston. The rubber element is designed to seal around most shapes and sizes of pipe and close off an open hole. During normal drilling operations, all the BOP’s preventers are open.
This allows tools to be lowered into the well and mud and drill cuttings to be circulated up out of the well, through the marine riser to the rig. When it’s necessary to shut in the well, a control panel on the drilling rig activates one or more of the BOP’s preventers, which are operated using high pressure water-based hydraulic fluid.
Once the well is shut-in, any pressurized fluids in the well hole can be safely routed through pipes and valves on the BOP to specialized pressure controlling equipment on the rig. To supplement the BOP, a diverter system is installed at the top of the riser. It functions similarly to an annular preventer by closing around the drill pipe. For crew safety, the diverter may be used to redirect any fluids in the riser away from the rig after the well has been shut-in.
Other significant players include Stabiltec Downhole Tools LLC; BILCO Tools, Inc.; Frank’s International N.V.; Varel International Energy Services, Inc.; Ulterra Drilling Technologies, L.P.; Baker Hughes; and National Oilwell Varco, Inc.