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8/11/2019 6 Mark Hewitt Interact
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CHALLENGES OF WELL RE-USEFOR GAS STORAGE
DEA Conference 3 June Hamburg
8/11/2019 6 Mark Hewitt Interact
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Presenter
Mark Hewett, Chartered Petroleum Engineer, InterAct
,
38 years oil industry experience in well engineering, withBaroid British Gas Amoco Shell & InterAct
Particular knowledge of Gas Wells in the Southern North
Sea & Land Operations in the UK & Brunei, including
Onshore Gas Storage Operations.
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Why are Gas Storage Wells needed?
To meet high gas demand periods, especially during winter
periods
Important considerations for gas storage wells
Market conditions, ie buy @ low price in summer & sell @high price in winter
Gas storage wells need to be near to customers, ie gas
transmission system or gas grid
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Types of Gas Storage Wells
1. Existing oil, gas or water reservoirs
2. Salt cavities
Both types of gas store usually have existing wells
1. Existing oil, gas or water reservoirs have production &
injection wells. Reservoir pressure is often below initial
conditions.
2. Salt cavities have leaching wells, which have circulatedsa ne water to eac out t e cav t es
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Reservoir Pressures
It is normal to use initial pressures as the maximum pressure
, ,
or gas reservoir
Use of hi her ressures than initial ressures are rare but
usually involve checking the strength of the cap rock using
formation integrity (FITs) & core tests
Gas cavity pressures are usually limited to pressure gradient<0.88 psi/ft or 2.0 (water = 1) @ the casing seat. These are
hi her ressures than conventional reservoirs due to the
strength of salt.
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What are the Requirements of Gas
Production & injection
High gas rates, so large tubing & completion components, eg
often 7” or 9.5/8”30+ year life
Gas availability @ short notice
Wells often shut in
Large pressure & temperature changes due to cyclic
operations
Well integrity
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Tubing & Completion Sizing
Ideally gas storage wells need to be designed from the
inside, ie tubing size will dictate well design & casing sizes
Tubing sizing will depend on production & injection rates
required, & gas transmission / gas grid pressures
Well numbers will also be related to tubing sizes, eg (x5) 7”
completions maybe equivalent to (x4) 9.5/8” completions, so
For existing wells, tubing size will need to be maximised
within the constraints of the roduction casin size. A re-
completion should be considered as a minimum when
converting a well to gas storage.
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Completion Components
7” & 9.5/8” completions are common in gas storage
Completion sizes are usually limited by the down-hole safetyvalves which are onl available in sizes u to 9.5/8” & can
be run with 9.5/8” tubing
Tubing & casings need to have premium gas tight
connections
Xmas trees, solid block are preferred for integrity reasons
Packers, fixed to tubing are also preferred for integrity
reasons
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Typical Gas Storage Completion
swab valve
kill win valve roduction win valve
upper master valve (fail safe)
lower master valve
tubing hanger with valve profile
sub-surface safety valve (fail safe)
9.5/8" tubing
annular fluid
packer
13.3/8" casing shoe
nipple
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Completion Stresses
Installation & operational tri-axial forces need to be
Ideally packers need to be fixed to tubing & accommodate
tubin to acker forces & acker to casin forces
Fatigue, especially of tubing connections, is a potential
issue due to cyclic operations, as completion will cool and
heat during production & injection operations
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Cement Bonds
Gas is more mobile than oil or water, & so good cement
gas storage wells
With existin wells cement bond & corrosion behind casin s
should be checked prior to re-completion
Casing with premium gas tight connections needed for all
wells, which needs to be checked for existing wells withcemented casings in place
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Metallurgy
Transmission or grid gas usually has <2mol% CO2 & <5ppm
2
L80 tubing often adequate, especially as gas from grid is dry,
the gas when in the cavity or reservoir
Low surface temperatures, ie below 0°C, need to be
considered for Xmas tree supply, & possibly for completionequipment below ground
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Corrosion / Erosion
Corrosion often less than expected due to dry gas from grid
However; if existing wells used, corrosion of existing casing
needs to be checked
Erosion is often a factor in gas storage wells, due to the high
gas flow rates & associated high velocities
,
used for gas storage
,
production occurs
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Well Integrity
Annulus pressures need to be continuously monitored on gas
,
Calliper logs should be taken routinely taken to keep a check
on tubin erosion / corrosion
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Summary
Gas storage wells have particular requirements & re-use of
Well integrity & production / injection gas rates are probably
the most im ortant arameters
Any questions?