We are seeking to optimize BOP test times by simultaneously
testing the choke manifold at surface and the BOP downhole within the same
test. An issue that we face is that for some tests, the Maximum
Anticipated Pressure at surface plus the hydrostatic of the fluid in the choke
lines exceeds 15,000 psi INTERNAL pressure downhole (rated working
pressure of the BOP). While the hydrostatic pressure of seawater at the
seabed reduces the NET pressure on the BOP to well below 15,000 psi, some have
expressed concern about exceeding the INTERNAL working pressure on the BOP
(i.e. could there be chambers within the BOP that are exposed to internal
pressure that do not gain the benefit of the hydrostatic back up?).
I was wondering how does other operators approach this issue –
do you or would you limit pressures to maximum rated INTERNAL pressure on the
BOP or are would you allow your pressure limits to be based upon the NET
loading of the BOP (internal – external pressure)?
BOP Pressure Testing - Optimization
Some years ago, a proprietary OEM of BOPs published the results of negative pressure tests on their BOPs operating in extreme water depths (10 000 - 12 000 feet). The technical investigation considered all stack components that would be subjected to external pressure. Overall, the results showed that there were no internal voids that would be damaged by the high external pressure acting. (hydrostatic seawater pressure) Here, we are discussing differential pressure across the BOP bodies and outlets (& auxiliary lines). Although you are considering the hydrostatic pressure being added to test pressures from the hydrostatic head of the test medium (presumably seawater), the head within the choke line is no different to the external seawater hydrostatic head.... so no concern there.
My concern regarding your proposed common pressure testing of both the C/K manifold and the stack simultaneously is that in the event of a detected leak on a particular test, your subsequent search for the leak source could well offset the time savings you may achieve in such a testing regime. In this scenario, there are an awful lot of possible leak paths presented to the test boundary.
I'd not do it but maybe concentrate in simultaneous operations: rig crew testing the C/K manifold whilst the main test activities are the wellbore pressure tests of the subsea BOP with the cement unit.