Understanding Shearing Blind Rams (SBR) and Interlocking Shear Rams (ISR) in Well Control Operations

In order to shear a string and shut the well in, two essential components used in Blow Out Preventer (BOP) are Shearing Blind Rams (SBR) and Interlocking Shear Rams (ISR), both of which play a vital role in containing well pressures, controlling blowouts, and shearing drill pipes when needed.

This article examines the key differences between these technologies and highlights the advantages of ISR over SBR.

Shearing Blind Rams (SBR)

Shearing Blind Rams (SBR) are the standard rams used in most BOPs. These rams are designed primarily for shearing operations, although they also function as blind rams, sealing the well after cutting the drill pipe.

Example: Shear Blind Rams (SBR) – Cameron Type U

Key Features of SBR

1. Single-Piece Design: SBRs consist of a single-piece structure where the blades are integral to the ram body. This creates a robust shearing tool, but one that may be limited when dealing with larger or multiple pipes.
2. Blade Geometry: The upper SBR is designed with a V-shaped cutting edge, while the lower SBR features a straight cutting edge. This combination ensures that the pipe is sheared effectively, but it also requires the lower portion of the severed pipe (fish) to fold over.
3. Sealing Capability: After shearing, the upper SBR houses a large blade packer that seals on the front surface of the lower SBR blade. This packer is designed to maintain a seal under normal operating conditions, preventing fluid or gas escape from the well.
4. Lower Fish Folding: One drawback of SBRs is that the lower fish must be folded over after the pipe is cut, which requires additional force. This folding mechanism is necessary to create a proper seal between the upper and lower blades.
5. Prolonged Packer Life: The large front packer in the upper shear ram is designed to seal against the front face of the lower shear ram. This prolongs the life of the packer and improves the overall durability of the ram assembly. However, the sealing mechanism may not be as reliable as that of ISR rams, especially in oversized wellbore cavities.

Interlocking Shear Rams (ISR)

The Interlocking Shear Rams (ISR) are an advanced shearing technology, offering an enhanced capacity over the standard Shearing Blind Rams (SBR). Their unique design enables them to handle more complex and challenging well conditions.

Example: Interlock Shear Rams (ISR) – Cameron Type U

Key Features of ISR

1. Improved Shearing Capacity: ISR rams can handle larger shear loads compared to traditional SBRs. This makes them ideal for situations where a higher shearing force is required, such as when drilling with larger or multiple strings of pipe.
2. V-Shaped Geometry: One of the most distinctive features of ISR rams is their V-shaped design. This shape maximizes shearing efficiency, allowing ISR rams to cut through drill pipes as large as 6-5/8 inches in outer diameter (O.D.).
3. Wider Cutting Range: The width of ISR rams allows them to shear through multiple strings at once. This ability is crucial when working in environments where multiple pipes or strings are being run into the wellbore simultaneously, offering a significant improvement over standard SBRs that may struggle with such complexity.
4. No Fish Folding Requirement: Unlike SBRs, ISR rams do not need to fold over the lower “fish” (the severed portion of the drill pipe). This reduces the force required to complete the shear, enhancing operational efficiency.
5. Pumpability After Shear: After the ISR rams shear the drill pipe, the severed portion remains open. This allows kill mud to be pumped down through the cut pipe, aiding in well control by equalizing wellbore pressure and potentially stopping a blowout.
6. Interlocking Mechanism: The interlocking mechanism incorporated into the ISR rams ensures that they can be used in oversized cavities without the risk of a leak, even at low wellbore pressures. This feature is essential in maintaining well integrity and preventing pressure leaks during critical operations.

Comparison Between ISR and SBR

The ISR and SBR both serve the same basic function—shearing drill pipe during well control operations—but the differences in design and functionality set them apart in terms of performance and versatility.

• Shearing Capability: ISR rams can handle larger pipes and multiple strings, making them more suitable for complex or high-risk operations. SBRs, on the other hand, are better suited to standard shearing tasks.
• Force Requirements: ISR rams require less force to shear because they do not need to fold the lower fish. This can save valuable time and reduce wear on the BOP equipment.
• Post-Shear Pumping: After shearing, ISR rams leave the fish open, allowing kill mud to be pumped through the severed pipe. In contrast, SBRs seal the well after shearing, which may limit options for pressure control.
• Leak Prevention: The interlocking mechanism in ISR rams ensures a more secure fit in oversized cavities, reducing the risk of leaks at low pressures. SBRs, while effective, may not offer the same level of sealing security in oversized cavities.

Conclusion

The Interlocking Shear Rams (ISR) provide an improved alternative to the standard Shearing Blind Rams (SBR) for well control operations, especially when dealing with larger or more complex drill pipe scenarios. Their advanced shearing capacity, reduced force requirements, and ability to maintain well control through open-ended fish make ISR rams a superior choice in many situations. However, SBRs still play an important role in standard well control operations and continue to be widely used due to their reliability and cost-effectiveness. For drilling operations requiring enhanced shearing capabilities and increased efficiency, ISR rams offer a compelling solution, ensuring both safety and operational success.

References

Cormack, D. (2007). An introduction to well control calculations for drilling operations. 1st ed. Texas: Springer.

Crumpton, H. (2010). Well Control for Completions and Interventions. 1st ed. Texas: Gulf Publishing.

Grace, R. (2003). Blowout and well control handbook [recurso electrónico]. 1st ed. Paises Bajos: Gulf Professional Pub.

U RaM-Type BOP. (n.d.-b). https://www.slb.com/products-and-services/innovating-in-oil-and-gas/well-construction/rigs-and-equipment/pressure-control-equipment/ram-type-bops/u-ram-type-bop