Basic Understanding about Cameron U BOP – Rams Blow Out Preventer

Suited towards surface or subsea applications, the Cameron Type ‘U’ preventer is one of well known wellbore pressure assisted ram preventers . It can come with a single ram (Figure 1) or double rams unit (Figure 2). When it comes to see whether the rams is in closed or opened position, this isn’t possible through observation alone and this is due to the operating rod’s tail end being enclosed inside the preventer itself. Since 1979, all Type ‘U’ preventers have required H2S service capabilities. One of key features of this BOP is a capability to pump open the bonnet doors. Once the four bonnet bolts have been removed, top-load ram changing is made easy by  applying closing pressure to push the bonnet out.

Figure 1 – Single Rams Unit – Camron U BOP

Figure 2 – Double Rams Unit – Camron U BOP

For various applications on surface or subsea, the Cameron U BOP actually is one of the most popular options for ram-type blowout preventers (BOPs) used around the world. Additionally, U type rams are wellbore pressure assisted. It means that the rams will seal better when wellbore pressure acts against the rams in a closed position.

The U BOP has many other useful features as listed below;

• On bonnet studs and nuts, the need for high makeup torque is eliminated because of the available bonnet seal carrier.
• To ensure consistent and even stud loading, the larger sizes will have hydraulic stud tensioning available.
• Even after a release in actuating pressure, the rams can be locked hydraulically and held mechanically closed because of the wedgelocks (locking mechanism that utilizes hydraulics). Before the BOP is opened with applied pressure, the wedgelock needs to retract and this can be ensured with sequence caps to interlock the operating system.

Pipe Rams

When using Cameron ram-type BOPs, Cameron pipe rams can be used and this helps to centralize and seal, depending on size, drill collar, casing, tubing, or drill pipe. With a sizeable reservoir of packer rubber and self-feeding in nature, Cameron pipe rams will remain in good condition regardless of environment. Furthermore, they’re suitable for H2S service (NACE MR-01-75) and the packers can be locked without fear of being dislodged by well flow.

For all Cameron pipe rams (except any U BOPs exceeding 13 -3/4 inches), CAMRAM top seals are standard. When concentrations of H2S are expected, and in high temperature service, CAMRAM 350 top seals and packers are also available.

Figure 3 – Pipe Rams Cameron U Type (Courtesy of Cameron)

Variable Bore Rams (VBR)

Variable bore rams will seal around various size of pipe as opposed to a pipe rams which can seal only one size of pipe. The VBR will remove the need for multiple sets of pipe rams (one for each pipe size), only one set of Cameron VBRs will be required regardless of the sizes of pipe or hexagonal kelly. With a single set, it’s possible to receive backup for different sizes; for example, a common set 2-7/8″ × 5″ and 5″ × 7″. Depending on ram range and tool joint size, some will have a limited hang-off capacity. Using surface pressure, it may be possible to force the tool joint through the ram packer but only when the outside diameter (OD) doesn’t exceed the variable ram’s maximum capability.

Figure 4 -Variable Bore Rams (courtesy of SLB)

Within their VBR and VBR II range, the following variable bore rams for U, UM, and UL are provided by Cameron (see the table below);

For those who need different sizes, these may be available from other manufacturers.

Some key interesting features are as follows;

•   Proprietary seals (CAMRAM) are the standard for well

•   Steel reinforcing inserts – when the rams are closed, these will rotate inwards and add support for the rubber (sealed against the pipe).

•   As per NACE MR-01-75, they’ll be perfect for H2S service.

Shearing Blind Rams (SBR)

To contain wellbore pressure, shear/blind rams can actually act as blind rams after cutting the drillpipe; a recess accommodates the pipe stub. Before shearing and if the situation allows, the pipe needs to be in tension and stationary. In addition to this, some cases will require a manifold pressure of more than 1,500psi while operators need to be sure that the tool joint isn’t opposite the rams. In terms of the shear process itself, the size and grade of the pipe can both be limiting factors (even when maximum manifold pressures apply). Unfortunately, for sour service, not all models of blind/shear rams will be suitable.

With Cameron SBRs, the pipe is sheared in the hole before the lower section (of the sheared pipe) is bent and this allows the rams to seal and close. For normal drilling or completion operations, the SBRs may have a use in closing on an open hole. With this in mind, its features contain;

• An ability to cut pipe several times while protecting the cutting edge.
• Integrated cutting edge within the single-piece body.
• Increased service life and reduced pressure for the rubber thanks to a large frontal area of the blade itself.
• For critical service applications, H2S SBRs are available and these will boast hardened high alloy as the blade material.
• All Cameron SBRs have CAMRAM top seals as standard.

With some similarities to SBRs, shearing blind rams called ‘DVS’ rams (double V shear) also exist and they have two main differences;

• They offer the largest-possible blade width while still fitting within the existing ram bores.
• After shearing, the lower section of the tubular will be folded with DVS rams and this allows a sealing between the lower blade and the blade packer.

Figure 5 – Double V Shear (courtesy of SLB)

Cameron U II Blowout Preventer

If you take the U BOP, and then make it suitable for subsea use, we find the Cameron U II BOP (suitable for 18-3/4-10,000 as well as 15,000psi WP sizes). Pressure-energised rams, just like other Cameron preventers, the seal can be maintained and the sealing force increased whenever hydraulic pressure is lost as the wellbore pressure acts on the rams. As wellbore pressure increases, seal integrity improves.

Important features of the U II BOP include;

• On bonnet studs and nuts, the need for high makeup torque is eliminated with the bonnet seal carrier.
• Even and accurate stud loading can be ensured consistently thanks to an internally ported hydraulic stud tensioning system.
• Normally, hydrostatic pressure can cause the wedgelock to unlock; this is removed by a pressure balance chamber.
• When actuating pressure is released and the ram is locked hydraulically, the rams can be held closed mechanically by hydraulically-operated locking wedgelocks (mechanisms).

Additionally, the design boasts a selection of rams depending on the application, hydraulically opening bonnets, and a forged body.

Figure 6 – U II Blowout Preventer (courtesy of SLB)

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.

Grace, R. and Cudd, B. (1994). Advanced blowout & well control. 1st ed. Houston: Gulf Publishing Company.

Watson, D., Brittenham, T. and Moore, P. (2003). Advanced well control. 1st ed. Richardson, Tex.: Society of Petroleum Engineers.

Watch, O., 2013. Offshore Well Blowout – Investigation Report. [online] Officer of the Watch. Available at: <https://officerofthewatch.com/2013/04/15/offshore-well-blowout/> [Accessed 8 August 2020].

Cable double-V shear rams. 2019. Cable double-V shear rams. [online] Available at: <https://www.slb.com/drilling/rigs-and-equipment/pressure-control-equipment/bop-rams/cdvs-ii-cable-double-v-shear-rams> [Accessed 21 June 2021].