What does an annular do on a BOP?

Ram blowout preventers (BOPs) and annular blowout preventers are two different types of well control equipment used in the oil and gas industry. While both types are designed to prevent blowouts and control the flow of fluids during drilling operations, they differ in terms of their sealing mechanisms, functionalities, and applications. Here are some key differences between ram BOPs and annular BOPs:

Sealing Mechanism:

Ram BOP: Ram BOPs use rigid blocks, called rams, to seal around the drill pipe or casing. These rams are hydraulically actuated and move horizontally to close around the pipe. The rams can be designed with various configurations, such as pipe rams, blind rams, shear rams, or variable bore rams, depending on their specific sealing and cutting functionalities.

Annular BOP: Annular BOPs, on the other hand, use a flexible, doughnut-shaped sealing element, known as an annular preventer, to create a dynamic seal around the drill pipe or casing. The annular preventer is typically made of rubber or elastomeric material and closes around the pipe by applying hydraulic pressure. It forms a complete circle around the pipe, providing a continuous and flexible seal.

Pipe Size Accommodation:

Ram BOP: Ram BOPs are designed to accommodate specific pipe sizes. They come with different sets of rams to match the size and configuration of the drill pipe or casing being used. Changing the rams in a ram BOP requires manual intervention to match the pipe size, which can take time.

Annular BOP: Annular BOPs offer more versatility in accommodating different pipe sizes. The flexible annular preventer can adapt to a wide range of pipe diameters without the need for changing out the sealing element. This flexibility allows for quicker and more convenient operations when the pipe size changes during drilling.

Dynamic Sealing Capability:

Ram BOP: Ram BOPs provide a static seal when closed around the pipe. Once the rams make contact with the pipe, the seal remains fixed in position. They are effective in providing a reliable seal as long as the pipe is properly centered and aligned.

Annular BOP: Annular BOPs offer a dynamic seal that can accommodate pipe movement. As the drill pipe rotates and moves vertically during drilling, the annular preventer adjusts its seal accordingly, maintaining a secure barrier. This dynamic sealing capability is particularly advantageous when dealing with a rotating or moving pipe.

Cutting Functionality:

Ram BOP: Certain types of ram BOPs, such as shear rams or pipe rams with replaceable cutting elements, are equipped with cutting functionalities. They can be activated in emergencies to cut and seal the pipe, preventing the uncontrolled flow of fluids.

Annular BOP: Traditional annular BOPs do not have built-in cutting capabilities. They focus primarily on providing a dynamic seal around the pipe. However, some annular BOPs may incorporate replaceable shear rams, allowing for pipe cutting in critical situations.

Space and Weight Considerations:

Ram BOP: Ram BOPs typically have a more compact design compared to annular BOPs. They require less space on the BOP stack and are generally lighter in weight. This feature is particularly beneficial in offshore drilling operations where space and weight limitations exist.

Annular BOP: Annular BOPs have a larger footprint compared to ram BOPs due to the size of the annular preventer. They require more space on the BOP stack and may be heavier. However, more compact versions of annular BOPs have been developed to address space constraints.

It's important to note that the selection of a ram BOP or an annular BOP depends on various factors, including well characteristics, drilling environment, operational requirements, and regulatory guidelines. Both types of BOPs have their advantages and are used in different applications to ensure well control and prevent blowouts during drilling operations.