wells 5_maersk introduction to well integrity

Well Integrity 17 December 2012 #1

Well Integrity

Nigel Snow


Agenda

Philosophy

Primary and Secondary Barrier Envelopes

Primary and Secondary Loads

Investigating Leaks and Leak Paths

Questions

Acceptable Leak Rates


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


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

Department 17 December 2012 #5

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


Small Bore Fittings and Lift Gas Lines


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.


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


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.


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?


Detecting a leak

All these leaks are detected at surface as an increase

in pressure in the wellhead at some annulus or control

lines.


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


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)