Leak testing criteria for low pressure well XMT and WH outlet valves


Looking for thoughts and current opinions on integrity testing for XMT valves on low pressure, mature wells close to EOFL.

The current procedure uses pressurised cavity test with water injected into cavity from KW outlet, and valves positively tested (UMV and LMV from above only - extended inflow test on these performed prior to any testing) but given the age of the trees we are struggling to get straight line tests as we have multiple slow leaks through both FWV and MV's that impact test interpretation.

In this case, we have used pressure testing from upstream side as an additional verification, but this again is not ideal.

I'd like to shift to a leak testing philosophy with defined acceptable leak rate, but the challenge is our low CITHP - in some wells only +/- 1000psi. Our flowline pressure is 300psi and we cant blow that down during testing, so don't want to vent the cavity to <300psi during testing (in case line pressure leaks in through FWV affecting the test) so only have 700psi dP across the valve we can use.

Using the API allowable leak rate for SSSV/SSV of 900ft3/hr, we could find ourselves reaching full CITHP downstream of the valve in just a few minutes, and still being within requirements and in theory having a successful test.

If this was sweet gas, I wouldn't be so worried, but we have significant H2S content in some wells so there is a HSE element to consider in addition.

My current thinking is to set a 10 minute leak test duration, with acceptance criteria of maximum downstream pressure increase of 50% of the initial dP applied across the valve and on a decreasing trend. In this case, we can demonstrate that the valve is restricting flow and pressure transmission without having to define an acceptable dP/dt ratio.. 

Can anyone on the forum comment on this thought process, or even better share what test acceptance criteria or philosophy they use for leak testing of low CITHP wells? 

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