Martin Blunt, Branko Bijeljic, Tara C LaForce, Stefan Iglauer, Ran Qi, Saleh Al-Mansoori, Chris Pentland and Erica Thompson

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Impact of capillary trapping on geological
CO2 storage

• Martin Blunt, Branko Bijeljic, Tara C LaForce,
  Stefan Iglauer, Ran Qi, Saleh Al-Mansoori, Chris
  Pentland and Erica Thompson

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Outline

• Field scale Streamline Simulation
• Core scale Column Experiment
• Pore scale CT scan

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Background

• Long term fate, how can you be sure that the CO2
  stays underground?

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Field scale - The streamline method
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Streamline method for CO2 transport
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Streamline method for CO2 transport

• Trapping model
• Pore-scale model matches experimental data.
• Kr is from Berea sandstone, which matches Oak
  (1990)s
• experiments.
• CO2/water system is weakly water-wet (Chiquet et
  al., 2007)
• contact angle (?) 65º.
• New trapping model (Juanes et al., 2006)

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Design of carbon dioxide storage
The ratio of the mobility of injected brine and
CO2 to the formation brine as a function of the
injected CO2-phase volume fraction, fgi.
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Design of carbon dioxide storage

• 1D analysis Numerical simulation vs. analytical
  solution

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Design of carbon dioxide storage
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Design of carbon dioxide storage

• 3D simulation Storage efficiency vs. trapping
  efficiency

Trapping efficiency the fraction of the
injected mass of CO2 that is either trapped or
dissolved
Storage efficiency the fraction of the
reservoir pore volume filled with CO2
The storage efficiency is highest for fgi 0.85,
which also requires minimum mass of chase brine
to trap 95 of CO2.
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Design Criterion

• Inject CO2brine where mobility ratio 1.0
• (fgi0.85 in this example).
• Inject chase brine that is 25 of the initially
  injected CO2 mass.
• 90-95 of the CO2 is trapped.

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Issues arising from field scale simulation

• Streamline-based simulator has been extended to
  model CO2 storage in aquifers and oil reservoir
  by incorporating a Todd-Longstaff model,
  equilibrium transfer between phases (dissolution)
  and rate-limited reaction
• Trapping is an important mechanism to store CO2
  as an immobile phase. Our study showed that WAG
  CO2 injection into aquifer can trap more than 90
  of the CO2 injected
• We have proposed a design strategy for CO2
  storage in aquifers, in which CO2 and formation
  brine are injected simultaneously followed by
  chase brine.
• Streamline-based simulation combined with
  pore-scale network modeling can capture both the
  large-scale heterogeneity of the reservoir and
  the pore-scale effects of trapping.

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Future work

• Injection strategy design
• Require better experimental data, since the
  trapping model used has a significant impact on
  the results.
• Design of an injection strategy to maximize CO2
  storage and oil recovery.

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CT Scanning

• A homogeneous sandpack was compressed and the
  porosity was determined via mass balance (F
  38,93).
• n-Heptane was injected when no more brine was
  produced, another CT scan was performed at the
  irreducible water saturation, Swi.
• CO2 was injected again. Gas injection was stopped
  when no more liquid production was observed.
  Another CT scan was taken.
• 30 pore volumes (PV) of brine were injected and a
  final CT scan was taken at the residual gas
  saturation Sgr .
• resolution 9 µm

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Sandpack at irreducible water saturation
Brine blue Sand red Oil - orange

• Oil penetrates on average mainly into the larger
  
• pores as expected by capillary pressure
• considerations.
• Thin water layer is visible on the rock surface
  as
• expected for quartz.
• Oil has penetrated into the middle of some
  pores.

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Sandpack at residual gas saturation
Brine blue Sand red CO2 - yellow

• The largest CO2 ganglia is continuously spread
  over the
• largest available pore.
• Though overall gas accumulates in the larger
  pores, a random
• distribution between large and medium size
  pores is
• observable.
• Several tiny gas bubbles are randomly
  distributed in
• the pore volume. Though they might originate
  from
• the segmentation process, it is thought that
  they are real.

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Vertical column experiments Sor vs. Soi

• Sand-packed columns were oriented vertically.
• 5 pore volumes of de-aired brine were injected to
  reach full saturation.
• Decane reservoir connected to top of columns and
  brine allowed to drain under gravity from the
  base. Decane enters the top of the column. No
  pumping.
• Equilibrium reached where both columns have a
  (theoretically) identical oil saturation profile
  versus height.
• One column removed for slicing and sampling
  Soi.
• Second column has brine injected from the base,
  Brine sweeps oil leaving an Sor. Coulmn sliced
  and sampled.

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Vertical column experiments Sor vs. Soi -
results