This message has been cross posted to the following Discussions: Well Integrity and Drilling .
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After reading John Turley's book 'The simple truth'.
The inflow test 'physical failures' in addition to people and organisational management, operating and further system failures were very evident in his book as to why things went ultimately so wrong.
In this topic area, I have first worked with companies that conduct inflow 'negative' tests all the time and others that do not.
These tests are primarily conducted during drilling, testing, after running liners or during abandonment e.g. before re-displacing a well/riser to seawater before pulling the SSBOP and marine riser. Also commonly conducted in well testing, well interventions, work overs operations etc to assure well integrity and design criteria is met for any down hole, well life cycle condition that could potentially exist.
Furthermore in some operating regions notably in offshore, deep and ultra deep water abandonment, inflow tests are mandated to be conducted on certain abandonment liners, plugs etc. So this is a requirement and very commonly done.
Rather that running a packer etc that is time/cost consuming, but can be implemented if a evident well integrity problem existed, e.g. a failed casing or component test. The simplest and most common method on a well not suspected to have failed, is to use a hydrostatic column 'volume' of sea water or often base oil (in oil based mud environments) displaced to a required depth to reduce the wells hydrostatic pressure, typically via;
- the tubular string in the hole
- or in deep and ultra deep water simply via a kill or choke line
to provide the required drawdown 'negative or inflow' test pressure.
Note: The draw down or inflow pressures required is often based on wellbore leak off tests for the section and components being tested with a further 0.xxppg or xxxpsi added negative pressure safety factor.
The inflow volume from the well is then generally recorded at the trip tank, and stripping tank and the time taken for a well to stabilise and not flow will vary. On many rigs we visually watch the flow, on others we also have remove hatches on trip tanks to physically be able to do this. So its quite a simple and straight forward test if people understand what is involved. Sometimes a diminished and zero flow is quickly established i.e. in 10-20mins. Typically both operator (as it's their well) and drilling contractor (note: the legal custodian of well control, the vessel and people on board) on a Mobile offshore drilling unit, will both require a longer period, to be fully satisfied. They would generally discuss based on the feel of the well or with engineers involved what return flow and volumes are expected. So before doing anything we have an assurance plan, a risk assessment etc and a full set of numbers, derivatives etc to what is expected based on what is known.
Essentially, zero or very little pressure should be observed before the line in question is displaced and/or then drawdown and finally opened to atmosphere, where once opened, the little pressure present, and return flow should diminish or stops to satisfy the well integrity 'inflow or negative test' requirements to verify that the well components being tested withstand the negative differential pressure that each has been subjected too.
As per leak off tests we would assure that return flow volumes and times are charted etc to meet the systematic quality check process then be properly recorded, signed off and fully documented.
No positive pressure more than an initial shut in or displacement effect should ever exist on any tubular string, choke or kill line that has been displaced with the lighter fluid. Hence why this is often referred to as a negative pressure test as the components in questions are being tested in the direction from the well to assure the integrity is provided as designed. We expect no pressure to be present and no increasing flow to result as these are both evident signs of a component failure.
On deep water SSBOP pressure gauges often can further relay, support and verify the reduced pressure at this point in the well, and further indicate all is as expected.
If a MWD/LWD or similar pressure tool is also present in the down hole tubular string, deeper well pressure from these tools can also verify and validate what has been present, to act and be used as a further safety and quality check.
If any difference in volumes, numbers or abnormal changes are observed. Those involved would take a time out for safety, get all involved both onshore and offshore in resolution, to then manage and control change as per companies policies and procedures. Often via an email confirmation as a minimum or through having to follow a more formal management of change process.
Other comments, observations, experiences to what organisation implement on these tests is therefore appreciated so that we all can evolve even better safe operating process and practices in this respect.
regards,
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Peter Aird
Drilling/Engineering/Training Consultant.
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