Most people associated with the industry are attuned with the term blow out.It implies pictures of a drilling rig with a column of oil shooting high above the derrick.Although blowouts do transpire from time to time, they are relatively rare occurrences.


We could define blowout as ben an uncontrollable escape of oil into the atmosphere.It occurs when fluid under pressure are released during drilling operation and which the various containment system fail to check.

Pressure is being exerted by fluids in the rock formations through which a drillbit makes a hole.Normally, the pressure of being exerted by the column of drilling fluid is sufficient to contain the formation fluid pressures.If however for any tenable reason the column of the drilling fluid drops below that of the formation fluids,this fluids otherwise called formation fluids will enter into the wellbore.An influx of formation fluid is reffered to as a "kick" and if not controlled leads to a blowout.


The escaping of fluids could flow up the annulus when drill pipe is in hole,or if the srting is out of hole.The fluid could simply flow through the open hole.The blow out prevention system must be capable of making a well safe under any circumstance..There are sub constituents of a bop stack
Choke and kill equipment
Bop stack
Bop operating system

This comprises of connections to the side outlet of the drilling spool fitted with one or more valves.From there a flowline passes to a branched manifold.At the manifold,mud flowing from well under pressure can be diverted throuh one of the chokes in the pit.
The chokes are actually orifice valves for maintening back pressure.Variable orifice is used to maintain back pressure the desired pressure.

A typival Bop preventer consist of the following items

Control comsole
Connecting pipework
Hydraulic oil reserve
The reservoir is simply a tank which contains reserve hydraulic oil used to close or open the preventers.From the tank,pumps take the fluid and develope the pressure necessary for preventer operation.The pumps are driven by air or electrically powered motors.The Bop is capable of being operated even though there exist no power to drive the pumps

Accumulators are used to store energy which can be used to actuate the preventers when rig power is unavailavle.
When control valve is opened, the pressure of the compressed ga,s forces the hydraulic oil through the connecting pipework to the preventer piston.The pump/ accumulator units are usually designed so that fluid charges are automatically maintained at desired pressures.


The Bop stack can be defined as an assembly of fittings and valves designed to close the top a well in case of any undesirable pressure.The stack is positioned beneath the rig floor directly under the rotary table.Since it must be capable of withstanding very high pressures,It mus therefore possess a secure base area.BOP types include:
Ram preventers,annular preventers ,shear rams and blind rams.
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