What Is A BOP Or Oil Rig Blowout Preventer?
Image From Osha.gov
Photo Of a BOP Stack
What Blowout Preventers Are Used For On A Drilling Rig
You will find blowout preventers, abbreviated BOP or the BOP stack, on all modern drilling rigs. They are designed to control underground pressure that may reach the surface and cause a blowout. The BOP stack consists of several different devices that either close in the annulus or open well bore or close in around or shear the drill pipe string.
The blind rams on a BOP are like a gate valve. They are made to shut in a well without drill pipe in the hole. The pipe rams close in around the drill string and prevent fluid and gas from coming up through the space between the surface casing and the drill pipe. This prevents a blowout by keeping the drill string securely down in the well were it belongs.
The shear rams are designed to cut off and leave hanging the drill pipe in the event that the pipe rams are not sufficient to hold back unexpected underground pressure.
The BOP or blowout preventer on an oil rig is controlled by a series of pressure vessels, valves and lines. An accumulator, as seen below, consists of controls and pressure vessels that are kept charged to control the rams and valves on the BOP stack. Some of these accumulators can be quite large on modern drilling rigs, unlike the small one below which I photographed on a small pulling unit / drilling rig in West Texas.
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The accumulator may be powered by a gas, diesel or electric motor which is used to charge up the various pressure vessels that control the rams and valves.
Small accumulator unit on a truck mounted pulling unit - drilling rig.
What Are BOP Drills On An Oil Rig?
Here is an excellent You Tube Video of a Polish and Indian rig crew conducting a BOP drill during tripping into the hole:
Oilfield blowouts happen when underground pressure is encountered. If the mud weight is not sufficient and the drill bit penetrates one of these zones the underground pressure will overwhelm the weight of the column of drilling fluid above the drill bit. Natural gas or fluid will force it's way to the surface and cause an uncontrolled release of pressure. This uncontrolled release of pressure can cause fire, explosion, damage to the rig and loss of life.
Blowouts on oil rigs are rare today but when they occur the results are disastrous. A blow out preventer can help prevent an uncontrolled release of underground pressure. BOP drills are similar to fire drills. Employees randomly are alerted, usually through a combination of horn blasts and hand signals to close the pipe rams on the BOP. One would not want to close the blind rams or the shear rams while the rig had drill pipe in the hole since this would damage the drill string.
BOP drills are held on most all modern drilling rigs to keep the crew ready to close the rams at a moment's notice if a blowout is about to occur. A kick refers to a pocket of gas that has traveled up the well bore, overwhelming the drilling fluid weight or mud weight.
If a kick occurs a crew member will be sent to close the rams. There is typically more than one set BOP controls on the drilling rig so that the rams may be closed from either the rig floor or down below. This is necessary in case the rig floor must be evacuated before the rams can be closed. I've been on rigs where BOP drills were conducted as many as five times a day. This is because the rig I was on was drilling in an area near Goliad Texas known for unpredictable underground pressure.
The BOP stack is a crucial part of any modern drilling rig. Blowout preventers cost many thousands of dollars and are costly to rig up and maintain. In spite of the cost they must be used to protect the rig and crew from a blowout situation.
Copyright 2008: Energyindustryphotos.com
For some photos of what can happen if an oil well blowout occurs see: Oil Rig Blowout Photos