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Subsea BOP Pressure Testing - Leak at Low but not Hi Pressure
05 July 2016

Hello,

Can there be a case that while pressure testing VBR at low pressure you observe a leak but while pressure testing at higher pressure you don’t observe the leak.

If yes what is/are reason/s for the leak. And can this impact the integrity/performance of the BOP.

Thank YOU.

5 answer(s)
rams.sunder
OIM
Gulf Drilling
Total Posts: 3
Join Date: 21/09/18
It is a clear indication of your top seal leaking. You must change it.
himansh1990
Technical Executive
Jubilant Enpro Private Limited
Total Posts: 15
Join Date: 25/09/13

Thank YOU Neil, Andrea, Paul for your response and for sharing your valuable knowledge.

Further considering a NEW VBR is used for exploration/appraisal well and all procedures followed including   using the ram locks on your surface wellbore pressure test against the VBRs. What are the likely chance of failure of BOP at subsea?

And what can be done to prevent this?

And if the problem is due to only this reason, is there a need to pull out BOP to surface for repair?

Thank YOU & Regards,

Himanshu



[email protected]
Training/Project Manager
Myspread Users
Total Posts: 15
Join Date: 07/03/16
Himanshu


VBRs are required to show that they can hold pressure low/hi on both the smallest OD pipe in the range and the biggest OD pipe in the range that is called for by the well programme predeployment & post-deployment then the smallest diameter test mandrel that will be used in the next drilled interval.  As with fresh annular preventer packing elements, freshly installed VBR rubber goods may be reluctant to show pressure tight integrity when new but performance usually improves with repeated functioning of the VBRs around appropriately diameter sizes of test mandrels (test joints)

Ram locks must be used for testing VBRs on the test stump and prior to stack deployment.  This means that once rams are closed and locks engaged, all lock/closing hydraulic pressure must be vented back to zero gauge.  The sustained closure of the rams on locks only subsea is limited to the BSRs and the desiginated hang-off ram shall also be tested locks only on the intial subsea BOP wellbore tests: after which no further ram locks test requirement during the subsea duration of the stack on 'that' well.


Some operators request to see demonstrated the pressure tight integrity capacity of the ram locks repeatedly subsea which is above and beyond API S53 but may be agreed mutually between contractor and operator.

You did not mention if you were using the ram locks on your surface wellbore pressure test against the VBRs.  You should be since it's a mandated requirement pre-deployment. 

Hope this helps...

Best Regards

Paul Potter / Registered Subsea Engineer (Ph.D)
andrea.martin.atanes
Drilling Engineer
Repsol
Total Posts: 3
Join Date: 12/04/16

BOP rams are designed to withstand wellbore pressures from below therefore, a higher pressure increases the sealing force to maintain a seal in the event of hydraulic pressure loss. This is the reason why sometimes when pressure testing them at low pressure they leak whereas at high pressure the seal is more efficient. Some rams have a front packer and an upper seal that is energized depending on the pressure that affects them from below.

As per API and Norsok both the low and high pressure test should pass to assure well integrity for exploration and appraisal wells, however as per Norsok for periodic testing of wells in production or injection phase a low pressure test is not required. Normally each company has its own maximum allowable pressure variation (i.e 3 psi/min, max pressure drop 5%...) so if the leak is not significant the pressure test would be acceptable.

Low pressure test should be in the range of 250 to 300 psi, hesitate to increase the pressure higher that this range and then bleeding off for pressure testing as the higher pressure could create a seal and it would not show the real result of the low test.


gds6ut
Drilling Supervisor
SPREADAssociates
Total Posts: 59
Join Date: 11/09/10
Absolutely, yes.

The LP test has failed and this has compromised the integrity/performance of the BOP and you will require to make repairs, take remedial action or possibly put a Management of Change deviation from policy in place.

The test still needs to be documented and recorded as a "fail".

For reference see: API Std 53 (Nov 2012), page 34
6.5.3.1.1 - LP test to 250-300psi
6.5.3.1.2 - "do not apply a higher pressure and bleed down to the low test pressure. The higher pressure can initiate a seal that can continue to seal after the pressure is lowered, therefore misrepresenting a low-pressure condition."

For remedial action, you may want to jet the BOP's and retry the test.  As these are VBR's you may want to look at the operating pressure and test pressures you are using and the size of the test mandrel with respect to the size range of the VBR's.

Cheers,

Neil Guthrie
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