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CHALLENGES OF WELL RE-USEFOR GAS STORAGE

DEA Conference 3 June Hamburg



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.



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



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



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.



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



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.



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



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



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



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



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



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



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



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?

6 mark hewitt interact

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