Workshop for Decision Makers on Direct Heating Use of Geothermal Resources in Asia,
organized by UNU-GTP, TBLRREM and TBGMED, in Tianjin, China, 11-18 May, 2008.
ENHANCED RE-INJECTION INTO
SANDSTONE RESERVOIRS USING CO2
AS A WORKING FLUID
PANG Zhonghe
Institute of Geology and Geophysics, Chinese Academy
of Sciences Beijing, 100029 CHINA
[email protected]
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Contents
• Re-injection into sandstone reservoirs
• Sequestration of CO2 in saline aquifers
• CO2-Water-Rock Interactions
– Experimental studies
– Numerical models
– Field site tests
• Future focus
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Sustainability of geothermal reservoirs
• Globally, it has been shown that re-injection of waste
water into sandstone reservoirs is difficult in geothermal
field management, though it is not impossible.
• In China, low temperature geothermal resources are
found mainly in sedimentary basins, such as the North
China Basin, Northern Jiangsu Basin, Guanzhong Basin
and Songliao Basin in Northeast China. Direct use of
geothermal heat is mainly dependent on this type of
geothermal resources.
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Geothermal Re-injection into Sandstone
Reservoirs
 In northern China, most of the geothermal
resources for heating is found in sedimentary
basins and
 They are hosted by either limestone or
sandstone aquifers.
 In the case of limestone, re-injection rate is as
high as 80%, but for sandstone aquifers, it is
<20%
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Sedimentary Basins in China
Songliao
Huabei
Subei
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Most of the low temperature systems in sedimentary basins
are formed by redistribution of heat flow as a result of tectonic
variations.
t(℃)
D
Z(m)
U
Heat flow
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Tianjin: geothermal re-injection versus
production <20% !
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Facts about Climate Change
1. Global air
temperature has
increased by
0.74°C in the 20th
century (IPCC,
2007)
2. Global warming has
serious
consequences
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Impacts of Climate Change
Melting glaciers: 20% of
ice in the arctic sea was
melt away in 20 years !
Climate Extremes:
heavy snow disaster in
south China last winter,
loss of 15 billion Euro !
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Sequestration of CO2 in saline aquifers
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Why CCS is Needed for China ?
 Projected no1
emitter in the world
by 2025 or sooner !
 Relies on coal for
75% of energy
consumption!
CCS=Carbon Capture and Sequestration
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CO2 emission sources in China
Coal burning power plants: 68.8%
3 bn tones/yr in 2005
Along the eastern coast
(Li, 2005)
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Sequestration of CO2 in saline aquifers
Bohai sea
Tanggu
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The government is taking actions
To lower energy consumption
by 20% per unit GDP by 2020
International Forum on CC and
S&T Innovations, Beijing, 24-25
April 2008: 700 million Euro
package !
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CO2-Water-Rock Interactions: lab
experiments
• Laboratory experiments: CO2–water–rock
interaction under reservoir conditions
• autoclave experiment and core-flooding
experiment:
– provides information on the mechanics of CO2–
water–rock interaction,
– reflect the change in porosity and permeability of the
rock.
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CO2-Water-Rock Interactions: lab
experiments
• CO2-water-rock interactions have been
investigated under various conditions:
 stimulated by EOR, experimental studies have been
carried out widely since the 1980s,
 flourished after the concept of CO2 “mineral trapping”
was proposed,
 pressure ranges from 1bar to above 600bar, and
temperature focus on that of the normal saline
aquifers(<80 C).
 some have reached 350 C (Shiraki and Dunn, 2000;
Rosenbauer et al., 2005; Bertier et al., 2006).
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CO2-Water-Rock Interactions: lab
experiments
 Results indicate that dissolution of supercritical carbon
dioxide into the experimental brine–rock system
 decreases brine pH,
 dissolute unstable minerals (feldspar, carbonate cement
and silicate texture) and
 precipitates carbonate minerals.
 A diversity of other fluid–rock reactions can also take
place between the mixed fluid and rock that differ from
the brine–rock system, depending on differences in
minerals, reactive surfaces, and assemblages exposed
to the brine.
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CO2-Water-Rock Interactions: lab
experiments
 CO2 core-flooding experiments present deferent results
with respect to change in porosity and permeability of
reservoir rocks.
 Decrease in permeability is concluded to be due to the
migration of authigenic clays to pore throats, or is
resulted from the crystallization of kaolinite in pore
spaces when few clay minerals were present originally,
which may be characteristic of CO2-flooding for
formations containing K-feldspar or other soluble
aluminosilicates grains.
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CO2-Water-Rock Interactions: lab
experiments
 Increase in permeability can be caused by
carbonate dissolution (Ross et al., 1981),
 but when it was offset by a reduction caused by
migration of clay minerals into pore throats,
there maybe no substantial change to
permeability (Bowker and Shuler, 1991).
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CO2-Water-Rock Interactions: lab
experiments
 Injection of CO2 can lead to dissolution,
transport and precipitation of minerals.
 Increase in the porosity and permeability of the
rock can be caused by dissolution,
 Decrease in the porosity and permeability of the
reservoir can be caused by precipitation.
 Thus, the change in porosity and permeability of
rock is affected mainly by the distribution of the
rock minerals and the chemical composition of
the brine.
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CO2-Water-Rock Interactions: lab
experiments
 As the CO2-water-rock interactions induced by
CO2-flooding of reservoirs are complex and
highly reservoir specific and cannot easily be
generalized (Holloway, 1997),
 experimental simulations performed on samples
of the targeted reservoirs is needed, serving as
input constraints for comprehensive
geochemical models and for validation of
numerical modeling.
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CO2-Water-Rock Interactions: Numerical
modeling
• Numerical modeling is employed to predict long-term CO2–water–
rock interaction, and corresponding changes in porosity and
permeability of reservoir matrix.
• Studies have shown effects of CO2 degassing on mineral
dissolution and mineral precipitation.
• Reactive transport modeling for study of CO2-induced mineral
alteration in the injection zone has shown changes in reservoir
porosity and
• Sequestration of CO2 in an arkose formation at a depth of about 2
km and 75 C.
• The mineral alteration induced by injection of CO2 leads to
corresponding changes in porosity.
• Significant increases in porosity occur in the acidified zones where
mineral dissolution dominates.
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CO2-Water-Rock Interactions: Numerical
modeling
 The porosity decreases within the CO2 mineral trapping
zone due to the addition of CO2 mass as secondary
carbonates to the rock matrix.
 The transport of dissolved CO2 and mineral alteration
generally decreases porosity, which could result in the
formation of a lower permeable barrier that would impact
reservoir growth and longevity.
 Significant CO2 could be fixed through precipitation of
carbonate minerals, which can offer geologic storage of
carbon as an ancillary benefit.
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CO2-Water-Rock Interactions: Numerical
modeling
Porosity distribution at
different times (Xu et
al., 2007)
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CO2-Water-Rock Interactions: Numerical
modeling
• The Nagaoka CO2 injection site demonstrates that the
water-rock interaction, which is generally regarded as a
longer-term phenomenon than various physical
processes, can also affect the reservoir system from the
initial stage.
• According to the modeling results presented (Sato et al.,
2006), the change in porosity of the reservoir rock was
estimated to increase by about 2% of initial values during
60a, using the dissolution rate and taking only anorthite
dissolution into account in light of relatively low
dissolution rate of other minerals.
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CO2-Water-Rock Interactions: Numerical
modeling
 The time frame of physical and chemical
changes is a function of reaction kinetics of
mineral dissolution and precipitation, which
requires further study.
 The extent of porosity decrease and amount of
CO2 mineral trapping depends on the primary
mineral composition.
 Sensitivity studies on different rock mineralogy
should be performed.
 Using natural analogues of CO2 reservoirs,
refinements on thermodynamic and kinetic data
should be useful.
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CO2-Water-Rock Interactions: Field testing with CO2
injection
• Frio brine field test: In year 2004, 1600 t of CO2
were injected at 1500 m depth into a 24-m-thick
sandstone section of the Frio Formation, a
regional brine and oil reservoir in the U.S. Gulf
Coast to investigate the potential for the geologic
storage of CO2 in deep saline aquifers.
• provides an insight into field-scale CO2–water–
rock interaction that implies substantial rapid
change in porosity and permeability of reservoir
rock.
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g
Hi the
in
20 miles
Industrial
sources
Fresh water (USDW) zone
protected by surface casing
Frio Test, USA
Injection zones:
First experiment 2004:
Frio “C” & “B”
Second experiment
2006: Frio “Blue”
Oil production
• Injection intervals: Oligocene fluvial
and reworked sandstones, porosity
24-34%, permeability 2.5-4.4 Darcys
• Steeply dipping 11 to 16o
• Seals several thick shales
• Depth 1,500 and 1,657 m
• Brine-rock system, no hydrocarbons
• 150 and 165 bar, 55 -65 C,
supercritical CO2
Hovorka, 2007
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Fate of CO2 in saline aquifers




(Adapted from: 2005 IPCC Special Report on Carbon Dioxide
Capture and Storage IGG-CAS
CO2-Water-Rock Interactions: Field testing with CO2
injection
 Fluid samples obtained from the injection and
observation wells showed that sharp drops in pH (6.5–
5.7), pronounced increases in alkalinity (100–3000 mg/L
as HCO3) and Fe (30–1100 mg/L), and significant shifts
in the isotopic compositions of H2O, DIC, and CH4
following CO2 breakthrough.
 Geochemical modeling indicated that carbonate and iron
oxyhydroxides dissolved into the low pH brine.
 This rapid dissolution of carbonate and other minerals
could ultimately create pathways in the rock seals or well
cements for CO2 and brine leakage (Kharaka et al.,
2006).
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Future focus: sandstone-linking the two
objectives in R&D
• Almost all oilfields in China have performed EOR
to some extent
• Most EOR used water flooding after primary
depletion; 30%~40% recovery
• A few CO2 flooding projects have been carried
out, 10%~15% recovery
• A few more are being planned
EOR = Enhanced oil recovery
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Future focus: sandstone-linking the two
objectives in R&D
 It is therefore suggested that future studies
should be directed towards providing firm
information through more tests at various scales
in sandstone reservoirs.
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Future focus: sandstone reservoirs in Tianjina good candidate for site testing
• As the world is taking actions towards mitigating
global warming, studies of CO2-water-rock
interactions in deep saline aquifers have been
flourished in the last decade or so.
• Results based on laboratory experiments and
numerical models have shown that porosity of
the formation will increase in the vicinity of
injection boreholes after injection of CO2. The
field test of CO2 injection into the saline aquifer,
the Frio Formation at Texas, USA, has also
indicated an increase in porosity of the formation
(Kharaka et al., 2006).
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Guantao formation
Geology of Tianjin geothermal fields
Minghuazheng Fm.
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• Thanks for your attention !
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