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1
CO2-EOR and Carbon Geo-storage; A UK Perspective
Jon Gluyas & Simon MathiasDepartment of Earth Sciences
Durham University
UKCCSC, Durham, UK
September 2012Email: [email protected]
2
Outline� Part 1 CO2-EOR in context
� Displacement & sweep efficiency
� Thief zones & gravity segregation
� WAG, SWAG and FAWAG
� Summary
� Part 2 Application & UK Potential
� The prize
� CO2 supply and facilities longevity
� Costing the earth & saving the planet
� The CO2-EOR heritage
4
Thermal methods
Steam injection leads to reduced oil viscosity.
Air injection leads to in situ combustion.
Gas injection
Includes injection of natural gas, nitrogen and CO2.
Injected gas displaces oil.
If reservoir pressure is sufficiently high the gas dissolves into the
oil leading to reduced oil viscosity and volume swelling.
Chemical methods
Polymers are used to change the viscosity of injection water
Surfactants (like detergent) are used to reduce surface tension
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� Improve displacement efficiency (micro-
scale)
� Improve sweep efficiency (macro-scale)
What are we trying to do?
Al-Shuraiqi et al.
12th European Symposium on IOR
From SPE 97270
Residually
trapped oil
Rock
grainsFlow of oil
Adapted from CO2CORC
Water
7
Electron photomicrograph of a
sandstone
1 mm
Pore-space
Pore-
throat
Displacement efficiency (micro-scale)
(Price, 1996)
8
If the rock is water wet, water adheres to the sides of
the pores due to surface tension.
Residual trapping
(Extracted from Tchelepi, 2009)
OilWater
9
If the rock is water wet, water adheres to the sides of
the pores due to surface tension.
As water moves upwards oil is displaced.
But as the water passes through the pore throat,
some of the oil is trapped.
(Extracted from Tchelepi, 2009)
OilWater
Residual trapping
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Surfactants (like detergent) reduce surface tension
allowing oil to connect into a continuous phase.
Application of surfactants
OilWater
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Viscous fingeringMobility ratio is essentially the ratio
of displacing to recovering fluid
viscosity. Very small (or large)
mobility ratios lead to poor sweep.
Ultimately, the front can become
unstable and viscous fingering can
occur.
Mobility ratio can be favourably
modified by increasing CO2 viscosity
by polymer addition.
[ ] 21)1(2 −+−= γγ DD hx
(Zhang et al. 1997, Chem Eng Sci 52:37-54)
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Poor conformance
ProductionInjection
CO2
Oil
CO2 often travels
preferentially through
high permeability thief
zones.
ProductionInjection
CO2
Oil
Sealing thief zones
with gel or foam can
lead to significantly
enhanced sweep
efficiency.
14
Identification of thief-zones
See for example Butler et al. (2009, Hydrogeology Journal 17:1849–1858) or Li et al. (2010, SPE 116286)
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Gravity segregation
ProductionInjection
CO2
Oil
De
pth
Permeability
De
pth
PermeabilityProduction
Injection
CO2
Oil
Use foam or gel to
reduce permeability.
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Application of gel for gas cut-off
Production
Gas
Oil
Water
See for example Al Dhafeeri et al. (2008, SPE 114323)
Localised application of gel reduces permeability
under gas cap leading to reduced gas production
due to coning.
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WAG: Water Alternating Gas
Pulsing of water and gas leads to reduced composite
mobility due to residual trapping of gas. However, gravity
segregation can still be an issue.
SWAG: Simultaneous Water And Gas
Simultaneous injection of water and gas at the top and
bottom of reservoir, respectively. Should reduce gravity
segregation but often limited by poor injectivity.
FAWAG: Foam Assisted WAG
Same as WAG but with surfactant. Combined surfactant and
gas leads to foam generation which reduces the mobility of
the gas.
See Aladasani and Bai (2010, SPE 130726) and Anwan et al. (2008, SPE99546)
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Summary� The aim of CO2-EOR is to mix residing oil with CO2 to
reduce oil viscosity and increase oil volume.
� The challenge is to improve displacement (micro-
scale) and sweep (macro-scale) efficiency of the CO2.
� Gravity segregation and thief zones are significant
problems for large carbonate reservoirs.
� Gels, foams and WAG strategies represent a range of
mitigating technologies (which reduce CO2 mobility),
which can be used in various combinations to
optimise various effects.
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CO2-EOR – Texas� Initiated 1970s in response to oil crisis� Texas at forefront of technology & leads the way today� Permian Basin in NW Texas is the primary injection area� 1000s km 32” pipeline & associated infrastructure developed� Natural & anthropogenic CO2 sources used
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CO2-EOR – Technology
� Water Alternating Gas (WAG)• CO2 injected to swell oil and increase fluidity• H2O injection to displace oil to production wells
� Gravity Stable Gas Injection (GSGI)• CO2 injected at field crest• Stabilising pressure and promoting gravity drainage
� Miscible flood – critical CO2 dissolved in oil • swelling oil, viscosity reduced surface tension reduced
� Immiscible CO2 displacement• Partial dissolution in oil may reduce viscosity substantially
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How much additional recovery?
� West Texas 4-12% of STOIIP (observed)• 60+ projects (~100 world wide)
� US DOE 7-14% of STOIIP (calculated)� Institute for Energy (Netherlands) 9-18% STOIIP of
UK, Norwegian & Danish fields (calculated)
� This study (2009) UK additional 3-8bn bbl� DECC (2012) UK mean additional recovery 5.7bn
(5-15% of STOIIP)
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How much CO 2 is used?
� 0.1 to 0.45 pore volumes injected� Typically 1 (net*) tonne of CO2 injected delivers 2.5 to 5
bbl oil (average 3 bbl)� Tapered WAG (decreasing CO2 volumes) most effective
*Net = total injected - recycled
26
UK Offshore Oil Reserve
Proven Probable P+P Possible Maximum
Cumulative Oil Production in millions tonnes (bnbbl)
3315
(24.9)
Estimated Ultimate recovery in millions tonnes (bnbbl)
3723(27.9)
361(2.7)
4048(30.4)
360(2.7)
4444(33.3)
https://www.og.decc.gov.uk/information/bb_updates/chapters/Table4_3.htm
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UKCS Recovery Factors ~45%
� High End - Piper – recovery factor >70%� Low End - Lyell – recovery factor ~5%
Jayasekera &
Goodyear SPE 75171
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UKCS & West Texas Oil Fields
UKCS
� Sandstones� Most > 2.7 km deep� Most > 90ºC� Light oil ~35-40API� Typically high quality
(permeability – 100s mD)� Line drive water floods for
secondary recovery� Low well density
West Texas
� Sandstones & dolomites� 1.2 to 1.8 km deep� 15-60ºC� Light oil 30-42API� Typically low quality
(permeability 4-16 mD)� Pattern floods
l� High well density
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UKCS vs West Texas
� West Texas – incremental oil recovery 4-12% of STOIIP
� CO2 is expected to be miscible (or nearly so) with current conditions in the UKCS oil reservoirs
� UKCS fields more permeable and at higher temperature than those in West Texas – both factors may favour the North Sea
From Goodyear et al, IEA EOR Caracas 2002
30
UKCS – The Prize
� Assuming UKCS:• Reserve of 30,000mmbbl• STOIIP 30,000/0.45 = 67,000mmbbl
� From West Texas 4-12% additional recovery of STOIIP• Yields 2,700 – 8,000 mmbbl technical reserves
• Requiring ~1 t CO2 per 3bbl*
� For ~3,000 mmbbl, ~1,000 Mt CO2 required
*range 2.5 to 5 bbl/tonne
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http://www.decc.gov.uk/en/content/cms/statistics/climate_change/climate_change.aspx
� Scotland 19mm tonnes� North East 21mm tonnes� Yorkshire 27mm tonnes
100km
UK oil province
UK Industrial CO 2 production 2007
32
Supply & Demand
� Assuming all industrial CO2 from the eastern UK could be available for CO2-EOR yields 60-70mm tonnes per annum
� Over a 15-25 year period (ie typical CO2-EOR project length) this would use 1 billion tonnes CO2 …. the quantity required to optimise CO2-EOR in the North Sea
35
UK Security of Supply
DECC publication 2008
Shortfall in 2010
~15 mm tonnes
Equivalent to
~300,000 bopd
Equivalent to
Initiating ~1/3 potential CO2-EOR projects
36
Costing the Earth?
� For the North Sea• There is no CO2 infrastructure• There is no ‘ready’ source of CO2
• The first project will be an enormous commitment
38
Saving the Planet
� 1bbl of oil contains ≡ 0.42 t CO2 after combustion� 1bbl produced by CO2-EOR requires between 0.4 and 0.2 t
CO2
� At best – the process is carbon neutral� At worst – the process is halving emissions
39
CO2-EOR Heritage
� The CO2 production from eastern UK could ‘power’CO2-EOR in the North Sea for 10-15 years per project, over ~30 year period
� It could deliver:• Improved security of oil supply• Infrastructure usable for carbon
capture • Increased tax revenues over
current projections
Deep aquifer storage area