CO2 Storage in Highly Depleted Gas Fields David S Hughes Technical Head Carbon Storage Senergy Ltd [e-mail]

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CO2 Storage in Highly Depleted Gas Fields
David S HughesTechnical Head Carbon
StorageSenergy Ltddavid.hughes_at_senergyltd.com

• International Workshop on Power Generation with
  Carbon Capture and Storage in India
• Delhi, 22-23 January 2008

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Senergy Limited

• Offer geological, petroleum/reservoir
  engineering, and wells consultancy to the oil and
  gas industry
• Established in 1990 as Reservoir Management Ltd
  and now incorporates Xcavo (Well Engineering) and
  Production Geoscience Ltd (PGL)
• 200 staff with offices in Aberdeen, London, Kuala
  Lumpur, Stavanger and Abu Dhabi
• Diversified into Carbon Transport and Storage
  including CO2 Enhanced Oil Recovery from 2003
• Developed significant income from this business
  stream
• Our clients for this work are oil companies and
  energy utilities

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Outline of Talk

• Units
• CO2 storage potential in depleted gas fields on
  UK Continental Shelf
• CO2 properties/pack up
• Overview of UK Southern North Sea (SNS) gas
  fields
• Case study of CO2 injectivity and storage
  capacity in a SNS gas field
• What does all this mean?

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Units

• 1 metric tonne (te) 1000 kg 2205 lb
• 1 million tonnes CO2 per year 51.8 million
  standard cubic feet per day (MMscf/d)
• 1 MMscf CO2 52.9 tonnes
• 1 tonne CO2 18.9 thousand scf (Mscf)
• 1 m3 35.31 ft3 (cf)
• 1 bar 14.5 psi (pounds per square inch)
• 1 mega Pascal (MPa) 145 psi
• 1 gm/cm3 (gm/cc) 1 tonne/m3 62.43 lb/ft3
• ºF ºC 9/5 32

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Units

• 1 metric tonne (te) 1000 kg 2205 lb
• 1 million tonnes CO2 per year 51.8 million
  standard cubic feet per day (MMscf/d)
• 1 MMscf CO2 52.9 tonnes
• 1 tonne CO2 18.9 thousand scf (Mscf)
• 1 m3 35.31 ft3 (cf)
• 1 bar 14.5 psi (pounds per square inch)
• 1 mega Pascal (MPa) 145 psi
• 1 gm/cm3 (gm/cc) 1 tonne/m3 62.43 lb/ft3
• ºF ºC 9/5 32

Standard conditions (oilfield units) 60F, 14.7
psia Density of CO2 0.1167 lb/ft3
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CO2 Storage Potential in Depleted Gas Fields on
UK Continental Shelf
Aquifer Gas Oil
Map BGS February 2005 Gas field storage from
Working Papers 85 and 100, Tyndall Centre for
Climate Change Research, January/February 2006
Depleted EIS gas fields 1.0 billion tonnes
Depleted SNS gas fields 2.8 billion tonnes
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CO2 Density
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Pack up with Depth

• Pack up is ratio of volumes of CO2 and
  hydrocarbon gas (measured at standard conditions)
  that can be stored in the same reservoir volume
• Calculated as function of depth using geothermal
  and hydrostatic gradients
• Not just ratio of densities at depth as gases
  have different surface densities
• Maximum pack up 4.6

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SNS Gas Fields

• 53 fields most Permian Leman Sandstone
• Proven geological trap for hydrocarbon gas
• Near to CO2 sources
• Existing infrastructure
• Well abandonments and pressure depletion may have
  compromised trap
• Aquifer influx may reduce capacity
• BGS estimate of CO2 storage capacity 2.8 billion
  te

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Case Study of Representative SNS Gas Field

• Depth 10,000 ft (3050 m)
• Initial Pressure 4500 psia (310 bara)
• Reservoir temperature 200F (93C)
• Porosity 15, permeability 50 mD
• 1 tscf (28 bscm) HC gas originally in place
• 90 recovery factor
• Pressure at start of CO2 injection 350 psia (24.1
  bara)
• Assumed CO2 disposal rate 200 MMscf/d (4 mill
  te/y)

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Estimate Storage Capacity, Injection Pressure,
and Reservoir Pressure

• 2 injection wells with 100 MMscf/d each
• 1D single well compositional model with radial
  grid

500 ft
Magenta - CO2
Green hydrocarbon gas
3700 ft
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CO2 Injection Rate and Cumulative CO2 Stored (2
Injectors)
Injection rate is maintained at 200 MMscf/d (3.86
mill te/y)
Cumulative CO2 stored over 25 years is 97 mill te
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CO2 Inflow Pressure and Average Reservoir Pressure
Difference between lines is the inflow pressure
drop which varies between 400 and 200 psi
Reservoir pressure limited to original pressure
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Pressure in Injector Tubing
CO2 arrival pressure
Initial gas field pressure
Gas
Liquid
Dense phase
Abandonment pressure
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Mismatch Between CO2 Arrival Pressure and
Required Inflow Pressure
CO2 arrives at base of tubing in this pressure
range
But only this pressure required to inject CO2
into reservoir
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Thermodynamics

• Important to evaluate processes using rigorous
  thermodynamics
• Neither constant enthalpy nor constant entropy
• Joule Thomson effects important particularly in
  expansion process at base of tubing
• Hydrate formation may be a possibility
• Engineering assessments of processes involved
  represent considerable challenge

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Interpretation of Dutch Sector Injectivity Test 1
(data from SPE 94128 2005)

• Injection rate 29,200 sm3/d (1.03 MMscf/d) so
  virtually no friction
• Bottom hole pressure rises from 39-49 bars
  (565-710 psia)
• Observed faster pressure increase bottom hole
  than measured at surface
• Gradient (plus friction) analysis shows that CO2
  was in gas phase throughout

15C
127C
3800 m
39-49 bara
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What Does All This Mean For CO2 Storage in
Depleted Gas Fields?

• BGS estimate that CO2 storage capacity is 2.8
  billion te in SNS and 1.0 billion te in
  Liverpool/ Morecambe Bay (East Irish Sea)
• East of England Energy Group estimate SNS
  practical capacity of 2.0-2.2 billion te in 15
  most suitable fields

An assessment of carbon sequestration potential
in the UK Southern North Sea case
study, Michelle Bentham, January 2006, Tyndall
Centre for Climate Change Research Working, Paper
85 Potential for storage of carbon dioxide in the
rocks beneath the East Irish Sea, Karen Kirk,
February 2006, Tyndall Centre for Climate Change
Research, Working Paper 100 Report on
Infrastructure, Availability and Costs for CO2
Transportation and Storage Offshore Southern
North Sea, EEEGR (East of England Energy Group)
for DTI, February 2006
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What Does All This Mean For CO2 Storage in
Depleted Gas Fields?

• This is significant capacity and an inviting
  target for CO2 injection particularly if existing
  infrastructure (including wells) can be reused
• Still significant technical problems to assess
  and overcome in order to realise this potential
• There is a particular issue with how to deal with
  the pressure mismatch at the base of the tubing

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Acknowledgements

• Senergy colleagues especially Irfan Sami
• Support and encouragement from clients to pursue
  the complex issues around CO2 storage in depleted
  gas fields
• Senergy Ltd
• Business Manager Carbon Storage John McCurry,
  john.mccurry_at_senergyltd.com, 01330 826621
• Technical Head Carbon Storage David Hughes,
  david.hughes_at_senergyltd.com, 01224 213440