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 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,
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.