What Is a BOP? Quick Introduction

Lesson Summary

A brief introduction to the blowout preventer and its role in protecting the well and crew.

This lesson is from the Well Control track and lasts 6:13 minutes. Watch the video first, then review the key points and test your understanding with the questions below.

Key Points

1. 1The BOP is installed above the wellhead
2. 2It shuts in the well upon a kick
3. 3It operates using hydraulic pressure from the accumulator unit

Written Lesson

Two barriers between the reservoir and the surface

In drilling, we rely on two independent barriers. The first barrier is the mud column: its hydrostatic pressure is higher than the formation pressure, preventing fluids from entering. If this barrier fails and a kick enters, the second barrier takes over: the blowout preventer (Blowout Preventer or BOP), which is a heavy assembly of valves mounted on top of the wellhead to shut it in tightly, after which we circulate the kick out in a controlled manner via the choke line.

Where is the BOP located?

In onshore drilling, the BOP Stack is installed on the (Wellhead) below the rig floor, and all pipes and tools pass through it. In floating offshore drilling, it is placed on the seabed and connected to the rig via the Riser, and is remotely controlled. In both cases, the principle remains the same: everything going down the hole passes through the BOP, so it must be able to shut in regardless of what is inside.

Main components at a glance

• The (Annular Preventer): a large rubber packing element that compresses to seal around almost any shape, or on an open hole when necessary.
• The Pipe Rams: two opposing steel blocks with rubber packers matched to the pipe size, closing around its body.
• The Blind Rams and Shear Rams: the former close the well with no pipe present, while the latter shear the pipe and then seal.
• The Drilling Spool and the Choke and Kill lines: lateral outlets allowing fluid discharge through the Choke Manifold or pumping into the well while shut in.
• Control panels: the driller's panel on the rig floor and a remote panel in a safe location.

Where does the closing force come from?

The BOP components are closed using hydraulic oil stored under pressure in the accumulator unit. This is an assembly of bottles containing precharged nitrogen gas (precharge), with pumps forcing oil against it so the gas compresses and stores energy. Upon a closure command, oil rushes to the pistons to actuate the rams or compress the annular element. The advantage of this design is that energy is stored in advance, keeping closure possible even if power fails or pumps stop.

P1 × V1 = P2 × V2 (Boyle's Law)

Worked example: a bottle with a gas volume of 10 gal, precharged with nitrogen to 1,000 psi, a system operating pressure of 3,000 psi and a minimum allowable operating pressure of 1,200 psi. At 3,000 psi the gas is compressed to 10 × 1,000 ÷ 3,000 ≈ 3.33 gal, so the bottle holds 6.67 gal of fluid. At 1,200 psi the gas occupies 10 × 1,000 ÷ 1,200 ≈ 8.33 gal, leaving 1.67 gal of fluid. The usable volume per bottle is therefore 6.67 − 1.67 = 5.0 gal. This calculation confirms that the number of bottles is enough to close the required functions with a margin, according to the standards your company follows.

What happens upon shut-in?

When a kick is detected, the driller shuts in the well according to the rig's approved procedure, usually on the annular preventer or the pipe rams with the choke line lined up. The shut-in pressures SIDPP and SICP then stabilize, and from them we calculate the kill mud weight. The BOP does not kill the well by itself; it gives us the time and control to circulate the kick out through the choke.

Why do we test it continuously?

The BOP is equipment we hope never to need, hence we must ensure it will work when required. Function tests (function tests) are performed to check the movement and closing time of each element, along with pressure tests (pressure tests) at low then high pressure, at intervals dictated by company policy and regulatory bodies. The crew practices shut-in drills (drills) until actions become automatic.

The figures and examples in this lesson are for educational purposes. On the job, always follow your company procedures and accredited training center instructions.

Lesson Glossary