API 16A Annular Blowout Preventer BOP Well Control Equipment For Drilling & Workover Operations

Annular Blowout Preventer – API 16A Well Control Equipment for Drilling & Workover Operations

Product Overview

The annular blowout preventer (annular BOP) is a critical well control device installed at the top of the BOP stack to seal the annular space between the drill pipe and the wellbore. Unlike ram-type BOPs that use steel rams to seal, the annular BOP uses a circular, steel-reinforced rubber packing element—often described as a “large rubber donut”—that can stretch or constrict to fit virtually any shape or size of pipe in the wellbore.

Annular BOPs were first introduced to the oil and gas industry in 1946 by Granville Sloan Knox. Today, they remain an essential component of every BOP stack, typically installed above a series of ram-type BOPs. While ram BOPs are designed to seal around a specific pipe size, the annular BOP’s ability to seal on a variety of pipe sizes is one of its key advantages over ram-type preventers.

All our annular BOPs are designed, manufactured, and tested in accordance with API Spec 16A—the international standard for drill-through equipment—and comply with NACE MR0175/ISO 15156 for sour service (H₂S) environments.

How an Annular BOP Works?

The annular BOP operates using a hydraulic control system. When hydraulic pressure is applied to the piston through the closing ports, the piston moves upward, forcing the spherical or tapered packing element to extend into the wellbore and create a seal around the drillstring or other tool.

Key Operational Capabilities:

Sealing around various tools – The annular BOP can seal around kellys, drill pipe, tool joints, drill collars, casing, wireline, and even irregularly shaped tools-.

Fully closing the wellbore – When no pipe is present in the well, the packing element can seal against itself to completely shut off the open hole-. However, it is important to note that sealing an empty wellbore reduces the rated working pressure of the sealing element by 50%.

Stripping drill pipe – When used with a hydraulic accumulator system, the annular BOP allows drill pipe to be moved up or down (or even rotated) through the BOP while maintaining a seal. This operation, known as “stripping,” is particularly valuable during well control operations when pressure must be maintained while running pipe in or out of the hole.

Key Features – Engineered for Reliability and Safety

1. Spherical or Tapered Packing Element with Massive Storage Volume

The packing element is the heart of the annular BOP. Our annular BOPs utilise a spherical or tapered packing element with a massive storage volume, low operating pressure requirements, and excellent sealing function. The packing element is moulded around a series of steel ribs or inserts that add strength and control the extrusion of the elastomeric material.

2. Hemispherical Bonnet Design for Stress-Free Operation

The bonnet is hemispherical-shaped, eliminating stress concentration points when bearing pressure. This design ensures structural integrity even under the most demanding downhole conditions.

3. Wedge Block Connection for Even Pressure Distribution

The bonnet and body are connected by a wedge block, ensuring that pressure is evenly distributed across the entire sealing surface. This reduces localised stress and extends service life.

4. Interchangeable Packing Element

The packing element is interchangeable with similar overseas products, simplifying spare parts management and reducing downtime.

5. Observation Hole for Packing Element Inspection

An observation hole is provided to allow operators to visually check the lifespan of the packing element without disassembling the BOP. This feature enables proactive maintenance and reduces unexpected failures.

6. Low-Position Piston with Wear Ring

The piston is set in a low position to provide a shorter moving distance, reducing wear and improving response time. A wear ring on the piston further extends component life.

7. Simple, Compact Design

Our annular BOPs feature a simple, compact design with only five major parts. The compact body saves space—height is typically 15 to 20% less than some other annular BOP designs. The simple hydraulic system requires only two hydraulic connections.

8. API 16A & NACE MR0175 Compliance

All annular BOPs are manufactured in accordance with API Spec 16A for drill-through equipment and NACE MR0175/ISO 15156 for H₂S service. This ensures the equipment meets the highest industry standards for design, materials, and testing.

Annular BOP vs. Ram BOP – Understanding the Difference

Annular BOPs are typically the first line of defence when a kick is detected, as they can be activated quickly and seal around virtually any pipe in the hole. Ram BOPs serve as the secondary sealing measure and provide additional capabilities such as shearing pipe in emergencies.

Technical Specifications – Available Models

Our annular BOPs are available in a wide range of bore sizes and pressure ratings to suit virtually any well condition:

Operational Applications

1. When Pipe is in the Well

The annular BOP seals the annular space between the drill pipe (or any other tool) and the casing or wellbore. It can seal on kellys, drill pipe, tool joints, drill collars, casing, wireline, and more-.

2. When No Pipe is in the Well

The packing element can be closed against itself to completely seal the wellhead. This is typically done when the drill string has been pulled out for tripping or when the well is shut in for extended periods.

3. Stripping Operations

When used with a hydraulic accumulator system, the annular BOP allows drill pipe to be moved into or out of the wellbore while maintaining pressure containment. The packing element will open slightly to permit larger-diameter tool joints to pass through.

4. Well Control Operations

After the well has been sealed, operators can perform essential well control operations through the choke and kill manifold connected to the BOP stack:

Circulating drilling fluid to condition the mud

Choking to control wellbore pressure

Killing the well by pumping heavy fluid

Releasing pressure safely

Contact us to order the right annular blowout preventer for your drilling or workover operation. We provide the correct bore size, pressure rating, and connection type for your specific well conditions—with full API 16A compliance, NACE MR0175 sour service capability where required, and on-time delivery.