Annular BOPs Explained

Annular BOPs are designed to provide the finishing touch essential to any oil drilling site. As the topper to a complete stack of oilfield equipment atop a well, annular BOPs pull a lot of weight to prevent leaks or disasters.

The importance of annular BOPs can hardly be overstated. But even if you know how important these blowout preventers are to your oilfield, it’s equally important to understand how they work. Let’s take a closer look at the history and functionality of annular BOPs.

How does an annular BOP work? How has it changed with time? Find out here. #BOPProducts Click To Tweet


An essential part of the oil industry for more than 35 years, annular BOPs have undergone design changes and improvements throughout their history. While most of these changes were relatively minor, one of the more significant changes occurred around 1960. At the time, annular BOPs were designed to be self-closing for an added layer of leak protection. This standard mechanism was very effective at keeping high-pressure oil contained. However, this same feature made it very difficult to force pipes through the packing units since the self-closing mechanism was constantly fighting against them. This also decreased the life of the packing units in question since the high pressure damaged them. As this problem became more common and more pronounced in offshore drilling projects, manufacturers began phasing out this self-closing feature. Most annular BOPs on the market today no longer have a self-closing mechanism.

How They Work

Annular BOPs are installed on top of other BOPs to allow sealing and control of the oil well. If no drill pipe or other BOPs have been installed yet, the annular BOP will be placed on the opening of the well itself. The elastomer sealant used is shaped like a large rubber donut and is designed to stretch or constrict to fit any size oil well, providing a remarkably tight seal. By pumping hydraulic fluid into different compartments within the BOP, oilfield workers can allow or restrict the flow of oil.

Pro Tip: A particularly large or high-pressure well might have several annular BOPs on top of the stack instead of just one to help contain the higher pressure.

Specially Designed Features

Every oil drilling site needs at least one annular BOP, and the exact measurements and functions required will vary depending on circumstances. That’s why it’s so important to design these BOPs with an excellent capacity for changes. Between replaceable bearings to decrease wear and tear, specialized sealant mechanics, and more, these devices can undergo virtually any change necessary to top your BOP stacks. Consult with the manufacturer to see what changes you might need.

A Reliable Piece of Equipment

BOP manufacturers recognize the important role played by annular blowout preventers and work hard to keep their products reliable, safe, and long-lasting. You can rest assured that a quality annular BOP will keep your oil drilling project safe and running for the foreseeable future.

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