Well Control System BOP Component

low 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:

1- An unexplained increase occurs in the drilling rate of penetration (drilling break), and

decrease in circulating pressure.

2- The mud flow meter shows an unexplained increase in the return flow of drilling fluid

from the wellbore.

3- 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.

1.1 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.

1.2 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