Basic Understanding about Cameron U BOP - Rams Blow ...

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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 , 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.

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.

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.

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.

References

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

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

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

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

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

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

Cable double-V shear rams. . 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 ].

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The BOP rams are the result of some eighty years of development in the BOP stack system. The first BOP ram was developed in the early s. The ram preventer will only seal on the specific condition for which the ram block is designed.

Rams are interchangeable between ram-type preventers of the same design and pressure rating. Casing rams are usually substituted for pipe rams before casing running or liner running operations.

Figure 1 : Ram Preventer (Hydril)

Most pipe rams can be locked in the closed position, operated manually and hydraulically, and support the weight of the entire drill string. Pipe rams cannot be installed upside down because they are designed to hold pressure from one direction only.

BOP Rams Components

The major parts of the ram preventer consist of:

1. The ram body houses all the parts that allow the ram preventer to operate.
2. The fluid connection is the port for the hydraulic fluid connection that operates the piston.
3. the side outlet which is a connection built into the ram body that allows fluid to be circulated into or out of the wellbore.
4. The piston rod mud seal is a secondary seal that keeps the drilling fluid types (OBM &#; WBM) from contaminating the inner seals on the piston rod.
5. The bonnet which is secured by the bonnet bolts allows access to the ram body to change the ram block.
6. The emergency piston rod packing is a grease injection port that allows a seal to be made on the piston rod should the primary seal begin to leak.
7. The bonnet seal is an elastomeric seal that prevents wellbore fluid under pressure from escaping.
8. The seal seat is a replaceable part that stops wear on the ram body by the operation of the ram block. It can be replaced in the field.

Figure 2: Hydril Ram with Manual Ram Lock

BOP Rams Types

There are two types of ram blocks with packer seals:

• Ram Block that seals on pipe
• Ram Block that can close on open hole.

Pipe Rams &#; Seal on the pipe

Ram blocks that seal on pipe (Figure 3) or wireline in the hole. The block is specifically designed for a particular size of drill pipe, tubing, casing, or wireline.

Figure 3: Ram Block for One Size Pipe (Hydril)Figure 4: Pipe Ram Block &#; Shaffer

Ram blocks designed for pipe should not be closed without pipe (drill pipe &#; heavy weight drill pipe &#; Casing) in them because the sealing elements may be damaged by extrusion.

Figure 5: Open pipe ramsFigure 6: Closed pipe rams

Variable Pipe Ram For BOP

The pipe ram block can also be a variable bore block (Figure 7) which can seal on a size range.

Figure 7: Varibore Bore Ram Block (Hydril)

Variable rams became available by . Also, these rams extend the versatility of the ram-type preventer by sealing on pipes of various sizes. This flexibility could eliminate the need for changing rams when running a tapered drill string or when testing with tubing. Variable rams use steel fingers that move inward to seal around pipe smaller than the ram body.

In general, all manufacturers of ram preventers offer variable bore rams (Figure 7) which can close and seal on a range of pipe diameters. These rams can be especially useful when a tapered string is in use or when substructure space limitations restrict the addition of another ram preventer. Also if an aluminum drill pipe is being used an effective seal cannot always be assured with regular pipe rams because the diameter of the pipe is larger near the tool joints than at the middle of the joint.

Variable bore rams have limited hang-off potential, depending on the pipe size on which they are sealing. For example, Cameron variable bore rams (13-5/8&#; U for 5&#; to 2-7/8&#;) will support 450,000 pounds of 5&#; drill pipe or 150,000 pounds of 3-1/2&#; drill pipe. Most variable bore rams are constructed in a similar fashion with the key element being a feedable rubber packer.

Blind Rams

Generally, there are two types of rams that do not have pipe openings and can be closed on open hole. The most widely used is the blind rams (Figure 8);

Figure 8: Blind Ram (Hydril)

Shear BOP Ram

The other type of BOP ram that we can close in the open hole is the shear ram. The shear ram (Figures 9 & 10) is designed to cut through the tubing, drill pipe, or casing, and in addition, it can seal on an open hole (Shear rams are used mostly in a subsea stack).

Figure 9 : Lower blade on shear ram (Hydril)Figure 10: Upper blade on shear ram (Hydril)Figure 11: Shear rams operationFigure 12: Shaffer Shear Rams

Shear/Blind BOP Ram

Shear/blind rams include a single-piece body with an integrated cutting edge to shear the pipe that is in front of the ram. Then, by bending the lower section of the pipe, the rams can close and provide a seal. It can also function as a blind ram and close & seal when there is no pipe in the hole. The operating pressure that you will need to shear pipe is 3,000 psi and the maximum size of pipe that you can cut is 5 ½&#; OD. Actually, the advantage of the shear ram is that you can use it many times without making damage to its cutting edge. Remember, we can always utilize it as a blind type during drilling operations

Figure 13: UI & UII BOP Shear/Blind Ram

Casing Rams

The casing rams are available to provide pack-off on the casing annulus when running casing. Casing shear rams are also available but may require &#; booster &#; pistons or higher closing pressure to assure shearing of certain-sized casings.

BOP Rams Features

Self-Feeding Elastomer Packing

The front elements of ram seals have steel &#;extrusion&#; plates bonded to the rubber. As the rams close the steel plates meet and begin to force elastomer to pack into the sealing area. When stripping operations, the front face of the ram sealing element will wear. This self-feeding feature will allow the sealing to be maintained during the stripping operation.

Figure 14: Self Feeding Action

Secondary BOP Ram Shaft Seal

On many ram preventers, there is a &#;weep hole&#; located on the underside of the preventer body. This hole is lined up with the &#;travel&#; of the ram. The weep hole is actually in line with secondary rod shaft seals and is there to indicate leaks in those seals. If needed, the cap screw is removed, and using an Allen wrench, the plastic sealant is injected through a check valve and around the ram shaft between seals to temporarily stop the leak.

Figure 15: Secondary Ram Shaft Seal

Secondary or Emergency Mud Seal

• The figure shows the secondary mud seal on an NL Shaffer ram-type BOP.
• The secondary seal is a plastic packing injected into an exterior groove around the ram shaft.
• As more plastic is injected and seals off between the ram shaft and the interior body of the preventer.
• The secondary mud seal should only be used in an emergency and is only usable once.

Figure 16: Secondary or Emergency Mud Seal

BOP Ram Locking Device

Many rams feature a manual locking device. The lock is activated after the ram is in the fully closed position. In this case, a ram manufactured by Hydril, is locked by clockwise rotation of the tail rod. The locking device travels down the lead screw and contacts the back of the piston mechanically locking it into the closed position. The locking device must be backed out in order to re-open the ram.

Should hydraulics fail, the locking device can be used to close the ram. If this is done, the ram can only be re-opened hydraulically.

Figure 17: Ram Locking Device

U Blowout Preventer Wedgelock Assembly

Figure 18: U Blowout Preventer Wedgelock Assembly

Hydril MPL Ram Lock

The MPL Locking mechanism is controlled by a unidirectional clutch and lock nut. The clutch maintains the nut and ram in a locked position until the clutch is disengaged by applying hydraulic opening pressure. This disengages the clutch plates permitting the lock nut to freely rotate and the ram to open. The ram will stay closed and locked even if the closing pressure is bled to 0 psi.

Figure 19: Hydril MPL Ram Lock

Shaffer Pos &#; Lock Ram Lock

As closing pressure is applied the piston along with the locking cone moves inward and closes the ram. When the piston reaches the fully closed position, the locking segments slide toward the piston OD over the locking shoulder because the locking cone is forced inward by closing hydraulic pressure and spring action.

The locking cone holds the locking segments in position. It acts like a second piston inside the main piston and is forced inward by closing pressure and outward by opening pressure. As opening pressure is applied, the locking cone moves outward causing the locking segments to slide toward the piston ID along a tapered locking shoulder. The piston then freely moves to the fully open position.

One note of interest &#; the Pos-Lock may not allow for self-feeding of ram rubber elements in worn rams as it locks in one position only.

Figure 20: Shaffer Pos &#; Lock Ram Lock

Closing Opening Ratios For BOP Rams

In the below table, there are different closing and opening ratios for different Ram BOPs in the market.

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Closing/Opening RatiosSIZEWP (psi)CAMERON &#;U&#; OPENCAMERON &#;U&#; CloseSHAFFER &#;SL&#; OpenSHAFFER &#;SL&#; CloseHYDRIL RAM OpenHYDRIL RAM Close7 1/16&#;3,.36.9&#;&#;1.55.47 1/16&#;5,.36.9&#;&#;1.55.47 1/16&#;10,.36.9&#;&#;1.78.27 1/16&#;15,.36.93.377.116.67.69&#;2,000&#;&#;&#;&#;&#;&#;9&#;3,000&#;&#;&#;&#;2.65.39&#;5,000&#;&#;&#;&#;2.65.39&#;10,000&#;&#;&#;&#;&#;&#;11&#;2,.57.3&#;&#;&#;&#;11&#;3,.57.3&#;&#;26.811&#;5,.57.3&#;&#;26.811&#;10,.57.37.627.112.47.611&#;15,.29.92.87.113.247.613 5/8&#;3,..542.15.213 5/8&#;5,..542.15.213 5/8&#;10,.374.297.113.810.613 5/8&#;15,.68.42.147.113.567. 3/4&#;2,000&#;&#;&#;&#;&#;&#;16 3/4&#;3,.36.8&#;&#;&#;&#;16 3/4&#;5,.36.82.035.54&#;&#;16 3/4&#;10,.36.82.067.112..618 3/4&#;10,.67.41.837.111.910.618 3/4&#;15,.19.71..852.157. 1/4&#;2,.37&#;&#;0.985.221 1/4&#;3,.37&#;&#;0.985.221 1/4&#;5,.16.2&#;&#;1.910.621 1/4&#;10,.17.21.637.11&#;&#;26 3/4&#;2,000&#;&#;&#;&#;&#;&#;26 3/4&#;3,&#;&#;&#;&#;Closing and opening ratios