Well Integrity 17 December 2012 #1 Well Integrity Nigel Snow
Well Integrity 17 December 2012 #1
Well Integrity
Nigel Snow
Well Integrity 17 December 2012 #2
Agenda
Philosophy
Primary and Secondary Barrier Envelopes
Primary and Secondary Loads
Investigating Leaks and Leak Paths
Questions
Acceptable Leak Rates
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Well Integrity Philosophy
• Two Barrier Envelope • Primary Barrier Envelope Breach is not acceptable
• Secondary Barrier Envelope Breach may be
manageable under certain conditions
• Primary Loads and Secondary Loads • Reservoir Loads
• Water or Gas Injection Loads
• Lift Gas Loads
Reference Documents • Norsok D10
• API RP90
• API 14B
• Maersk Oil Well Barrier Standard
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Barrier Envelopes
Well barriers are pressure-containing envelopes that prevent fluids or gases from flowing
unintentionally from the formation into another formation or to surface.
The primary barrier shall contain the fluids and gases at all times during the life of well
cycle, and under all load conditions
The secondary barrier shall contain the fluids and gases in the event of a breach of the
primary well barrier
The well barrier envelope changes during the wells life cycle depending on the wells
functionality and also well activity such as intervention
Well barrier acceptance criteria can change depending on well activity
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Production Casing is the secondary barrier to the reservoir and Primary barrier to Lift Gas
Secondary barrier to Lift Gas
Barriers to Lift Gas
Production
Annulus
Intermediate
Annulus
Production
Annulus
Intermediate
Annulus
Well Integrity 17 December 2012 #6 Department
Testing Of Barriers
• Positive Test vs API Inflow Test
• Split Gates vs Slab Gates
Barrier Envelopes
• Lift Gas Lines
• Instrumentation Lines
• Small Bore Fittings
Barrier Envelopes
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Small Bore Fittings and Lift Gas Lines
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Primary and Secondary Loads
The Primary Load is the cyclic combination of pressure, temperature, tensile and
compressive loading of a barrier envelope during normal operations.
For Example;
Maximum closed in THP is a primary load.
Maximum Lift gas pressure is a primary load.
The Secondary load is an abnormal load that is not normally seen, however in theory
could be possible should several events combine at the same time to produce the effect.
For example, a high pressure spike as a result of a sudden water injection breakthrough
is a secondary load.
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Barrier Test Requirements
Primary Loads to the Primary Barrier are assessed against the actual test pressure of
that barrier divided by a safety factor of 1.1
Secondary loads to the Primary Barrier are assessed against 80% of the published yield
pressure
Both Primary and Secondary Loads to the Secondary Barrier are assessed against the
published yield pressure divided by a safety factor of 1.2
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Leak Investigation Objectives
Note: any temperature, thermal expansion effects
have first to be eliminated as the cause of the
increased bleed down frequency
Confirm the presence of the leak
and rule out any surface related
pressure sources or piping irregularities.
Confirm wellhead seal and hanger
integrity.
Determine the leak rate at stable conditions.
To determine the source of the
pressure causing the leak.
Determine if the leak is affected by
neighboring annulus sections.
Perform and record at least two pressure build up profiles of
the annulus section.
Perform a tank volume calculation.
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Acceptable leak rates (2nd Barrier)
•The leak rate is below the API-14B limit (24 lt/hr or 900 scf/hr) for SSSV.
•A procedure is in place to ensure that the maximum allowable pressure limit
cannot be exceeded.
•The annulus bleed down frequency can be safely managed by platform personnel.
•Confirmation that the temporary leak is stable over time.
•Formation of a working group to investigate possible options and associated costs.
•Installation of additional ESD shut down pressure sensors.
•Formal Risk Assessment that may recommend other additional precautions.
Well Integrity 17 December 2012 Department #12
Questions?
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Detecting a leak
All these leaks are detected at surface as an increase
in pressure in the wellhead at some annulus or control
lines.
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Measuring a leak
Gas Leak
• Flow prover
• Data logger: Records the pressure at all annulus,
tubing and flow temperature over time
• Gas leaks in a controlled manner through an
oriffice
• Measuring the pressure diferential before and after
the orifice, the flow can be calculated
• Studying the build up profiles the depth of the
leak can be estimated
• Many production casing leaks only exist
when gas lift is introduced
Liquid leak
• API Bucket
• Stopwatch
• Flow Prover
• Data logger: Records the pressure at all annulus,
tubing and flow temperature over time
The Guidelines for Annulus Pressure Monitoring and
Bleed Down have been in place since 1996, the
current version was last revised in November 2001
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Interpreting the Results
Possible Outcomes: Production Annulus Investigation
• Leak identified at SPM
• Leak identified in tubing
• Leak identified around production packer
Possible Outcomes: B-Annulus Investigation
• Leak source identified as Production Annulus lift gas
• Leak source identified as B-Annulus shoe (shallow gas)
• Leak source identified as 9-5/8” micro annulus problem (main reservoir)