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Trapped pressure whilst testing BOP on stump
24 October 2013
Hi folks

We'd appreciate your input into the following tricky situation which we were informed about today.

Whilst testing the Shaffer SLX Double 18¾" 15k surface stack on the test stump, we have found that the 15,000 psi test pressure (applied via instrument line using a test pump) cannot be bled off.  We strongly suspect that the line is blocked.

The closed rams are lower 5"" pipe rams. Based on the published figures we would need > 9000 psi accumulator opening pressure to open the rams, which is not possible with the 3000 psi accumulator system that we have on the rig.

Have any of you experienced this kind of problems before, what solutions did you come up with and which one(s) worked ?

Thanks and kind regards

Dave


7 answer(s)
admin
Managing Director (rp-squared.com)
Relentless Pursuit Of Perfection Ltd.
Total Posts: 377
Join Date: 10/01/05
This just came in via a member contacting an expert in Houston ..

"That´s an easy one to fix”¦
  1. Fill the Choke line on the BOP/LMRP with water and Install the BOP/LMRP riser testing cap on the LMRP adapter and connect up the test pump to the choke line
  2. Close the set a rams above the closed lowers. The choke line should be ported above the lower rams normally if for some reason the kill is above the lower rams then line up on the kill.
  3. Line up on the Choke line (open failsafes)  and pressurize to 15K. The lower rams now are balanced and the can open the Lower rams.
  4. Bleed the 15k pressure as normal and open the upper ram
 
(They probably didn´t wash the BOP ID before setting in on the stump)"
______

Kind regards

Dave
gds6ut
Drilling Supervisor
SPREADAssociates
Total Posts: 53
Join Date: 11/09/10
I guess that the test line goes into the test stump and you are closed in on the lowest set of rams.  On a Danish drilling contractors rig about 10+years ago they had the same problem - they ripped off the 'ram foot' on the end of the ram piston getting the BOP opened.

I guess that the test port just goes straight into the test stump - you need a little vertical 'trombone' u-pipe that points downward to prevent 'hoovering' up and trash that is sitting on the test stump.

Although the test stump may be spotlessly clean before you land the stack and button up the bottom connector, when you function the rams, trash can fall out of the ram cavities onto the stump.

Can't help you getting them open, but going above our test pressure and bleeding down very slowly might work (but may end up with an even higher pressure trapped).

Cheers,


Neil Guthrie


odyssea
Sr Subsea Equipment Engineer
Shell
Total Posts: 5
Join Date: 24/09/13
Look to see if there a check valve in the line between the BOP and bleed off valve or is there a check valve on the output of the hand pump that can prevent bleeding off pressure.
Billabel
President
Abel Engineering
Total Posts: 5
Join Date: 18/11/11
I assume you have no means to conventionally bleed down the pressure (line with a valve, needle valve....).

In the past with a similar situation, we drilled a hole in the ring gasket of a blanked off flange. In this way you have a very small choke to control the bleed off rate. Alternatively you might consider a hot tap of the flange. However, either will require an experienced person (can be found in the snubbing business CUDD, et al). Well control companies like WWCI,  Boots n Coots can do this also but at a cost (as you can imagine). If I could see the arrangment I might be able to offer more suggestions. Good luck!
attema
Drilling Superintendent
Myspread Users
Total Posts: 19
Join Date: 24/05/06
Could you close the Upper Pipe Rams. Presurise the cavity between the rams with a pressure higher than 15,000 psi. This should push the Lower Rams of their upper seat. The 9K acc. pres. would largely be required to overcome the friction of the upper seal. By pushing the ram down the friction will be reduced/lost and the ram can be operated at lower acc. pres. I suggest that before applying pressure to the upper cavity the operator confirms the ability to bleed-off. Good luck.
dadinbrazil
Subsea Superintendent
SPREADAssociates
Total Posts: 4
Join Date: 28/07/11
If there is still 15K psi pressure below the pipe rams the last thing you want to do is attempt to open the rams. The button head on the ram shaft could crack or worse, fail completely. It's common occurence for the test port in the test stump to plug off with cuttings or debris that accumulated in the ram cavities and annular cavities. If possible, it's very good practice to open all ram doors and clean/inspect rams before doing a pressure test, such as when subsea BOP stacks are on surface. For surface BOP stacks jetting the BOP ram cavities prior to testing would clean out debris. 
You can try several things:
1) try to pump through the test line at very slow rate. It's sometimes possible to dislodge the blockage up into the BOP. Going 10-15% above rated working pressure of the BOP will not affect the equipment.
2) Open a failsafe valve, or wing valve, to relieve the pressure, keeping the area clear of the discharge. This will be a sudden, but low volume, release of pressure and will likely require repair of the valve seat seals. Use the outer valve to release the pressure, keeping the inner valve intact to hold well bore fluids after the pressure is bled off. If any piping is connected to the valve outlets it should be removed prior to releasing pressure. Using a valve to release pressure will cause less damage to BOP equipment than trying to open the rams.  
3) To prevent blockages of the test port install a cover similar as described in Vetco bulletin H051491, attached.
4) In future bleed off the pressure very slowly. Sudden bleed down will draw debris into the test port.
Hope this helps.
 
Documents uploaded by user:
Vetco Bulletin H051491 Test Port Cover.pdf
John_McNab
Completions & Workover Manager
SPREADAssociates
Total Posts: 10
Join Date: 11/02/10
Dave,

Can you close any rams above (other 5½, BSR?), equalise across the closed 5½ rams, open them, then bleed off the entire pressure envelope through the line used to equalise above the closed 5½ rams?

I take it there is no needle valve on the test stump to isolate and remove the hose?

John
_______

Answers from Dave:
1.  Great idea about equalising - I've passed it on and will let you know how we got on.
2.  Don't think there's a needle valve to isolate the hose.
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