Well Control System BOP Component

Blow out Preventer (BOP) System:
A blowout is an uncontrolled flow of formation fluid (oil, gas or water) under high
pressure from a subsurface formation to the surface. The occurrence of a blowout is
a drilling disaster. Lives may be endangered, and severe damage may occur to the
rig and the surrounding environment. A blowout usually begins as a kick which is an
intrusion of any high-pressure subsurface formation fluid into the wellbore. If the
crew does not handle it immediately and correctly, this intrusion may lead to a
blowout.
In order to stop a kick from becoming a blowout, the blowout prevention (BOP)
system is used. The BOP system has two major functions:
1. To seal off the wellbore when a kick occurs.
2. To maintain sufficient back pressure in the wellbore to prevent further flow of
formation fluids while steps are being taken to restore the well to a balanced /
overbalanced condition.



Controlling formation fluid intrusion:
If the flow of formation fluid is minor, it can be handled by directing the circulation
of drilling fluid through the conditioning equipment, which will assist in expelling the
entrained gases more rapidly. If the flow of formation fluid is severe, the BOP is
activated. This action is called Shutting In the well. The choke manifold is used to
control the back pressure when a kick occurs by limiting the escape of fluid from
the wellbore, as well as preventing any further flow of formation fluids. Once the
flow is stopped, heavy drilling fluid is pumped into the well, thus preventing any
further intrusion, and regaining control over the wellbore.
Blowout prevention and control:
The best prevention against possible blowout is the use of drilling fluid that is properly
weighed and has the correct density so that sufficient hydrostatic pressure is exerted
against the wellbore walls (this is known as primary well control). This prevents any
formation fluids from entering (fluid intrusion) the wellbore.



Kick:
When the hydrostatic pressure of the mud in the wellbore becomes less than the
formation pressure, formation fluid enters the wellbore and begins to rise to the surface.
This is called a kick. There are a number of observable warning signs when a kick
occurs:
**  An unexplained increase occurs in the drilling rate of penetration (drilling break), and
decrease in circulating pressure.
**  The mud flow meter shows an unexplained increase in the return flow of drilling fluid
from the wellbore.
**  The mud Pit Volume Totalizer (PVT) indicates rapid rise in pit volume. All of the above
are indicators of formation fluid intrusion into the wellbore. If left uncontrolled, a blowout
will occur.



Major BOP Components:
The BOP system on a rotary drilling rig is a pressure control system designed
specifically to provide the secondary well control should the primary well control
fails. The system consists of four major components:
1. The blowout preventer (BOP) stack
2. The accumulator unit
3. The choke manifold
4. The kill line
1. BOP Stack
For a surface blowout preventer (BOP) stack, it is located at the casing or wellhead
directly under the rotary table. The BOP stack is an assembly of special devices that
may include:
- Annular preventer
- Pipe ram preventer
- Drilling spool
- Blind / shear ram preventer
- Casing head housing



The BOP stack can be assembled in any number of arrangements and it is usually
dictated by the potential problems that are anticipated at a particular drilling site.

Annular Preventer
The annular preventer is located at the top of the BOP stack assembly. It contains a
steel-reinforced rubber packing elements that close by moving toward each other to
seal on drill pipe, drill collar, kelly or open hole. The annular preventer has the
ability to exert pressure shut-off on any shape or diameter that might be in the
hole, and even the open hole itself (though this is not encouraged). They can exert
a shut-off on square or hexagonal kelly, and permit slow rotation as well as vertical
movement of the drill pipe while under pressure.

Ram Preventer
The ram preventer closes the annular space outside a string of drill pipe in the well by
semicircular openings that fit the pipe diameter for which it is designed. Pipe rams
will have openings that match the diameter of the pipe for which they are designed. The
majority of ram preventers close only on specific sizes of pipe, tubing, and casing or on
an open hole. They are designated as follows.
1. Pipe rams which close only on pipe of sizes which they match.
3. Shear rams which designed to cut the drill pipe when it closes
4. Blind rams which is used to close the well completely when there is no pipe inside
the wellbore.





1.3 Drilling Spool
A drilling spool is a spacer between the preventers. They provide hook-ups for the
choke line and kill line.
1.4. Casing head
The casing head is an attachment at the top of the casing on which the BOP stack is
engaged. A wear bushing (sleeve) is placed across the wellhead connection to prevent
damage while drilling and tripping with the drill pipe and downhole equipment.
1.5 Choke Manifold
The choke manifold is an assembly of high pressure flanged pipe fittings with several
lateral outlets controlled by manual valve and/or remote operated valve (controlled from
a choke panel on the rig floor). It is attached to the BOP stack by a high pressure line
called the choke line. When activated, the choke manifold assists in maintaining
sufficient back pressure in the wellbore to prevent any further formation fluid intrusion.
1.6 Kill Line
The kill line is attached to the blowout preventer stack directly opposite the choke line.
Heavy weight drilling fluid is pumped into the wellbore through this line to balance
formation pressure.
1.7 Accumulator
The two main functions of an accumulator unit are to store hydraulic fluid under
pressure and to operate of all BOP functions. The reason for having stored pressure is
that, in case of a major incident with loss of power supplies on the rig, the well can still
be secured by operating the required BOP function. The unit can be activated from a
remote panel on the rig floor or from the accumulator on the unit itself in case the crew
must evacuate the rig floor.