John Kaldi, Ric Daniel. Eric Tenthorey, Karsten Michael, Ulrike Schacht, Andy Nicol, Jim Underschultz, Guillaume Backe

© CO2CRC All rights reserved

Caprocks Systems for Geological Storage of CO2

Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC)

IEAGHG Combined Networks Meeting:Modelling and WellboreIntegrity

Perth, WA, Australia27-29 April, 2011

Established & supported under the Australian Government’s Cooperative Research Centres Program

Supporting Partners: Global CCS Institute | University of Queensland | Process Group | Lawrence Berkeley National Laboratory

CO2CRC ParticipantsRESEARCH PARTICIPANTS

INDUSTRY AND GOVERNMENT PARTICIPANTS/FUNDERS

Recent IEAGHG Studies on Caprocks

• Caprock Systems for Geological Storage of CO2

– (this study)

• Pressurisation and Brine Displacement, Permedia, Canada– Literature review and modelling to assess pressure

and brine displacement effects in DSF storage– Implications for capacity and injectivity

Caprock Systems Study: Terms of Reference

• High-level overview of caprock systems for CO2 Storage– Literature review to assess current state of knowledge– Identification of knowledge gaps and R&D priorities

• Caprock “system” (key parameters controlling confinement)– Petrophysical– Geometric– Geomechanical– Faults & fractures– Geochemical– Hydrodynamic

• Risk assessment of “system” – What do stakeholders (operators, regulators, community) consider

Potential Escape Mechanisms

A: CO2 escapes through thin or eroded section of seal, B: CO2 buoyancy pressure exceeds capillary pressure and passes through the seal, C: CO2 migrates from reservoir and up transmissive fault, D: CO2 escapes up wellbore via poorly completed injection well and into shallower formation, E: CO2 escapes up wellbore and into shallower formation via poorly plugged old abandoned well, F: Hydrodynamic flow transports dissolved CO2 out of closure, G: CO2 migrates updip beyond influence of regional seal

(modified after Benson et al., 2004)

Seal Potential

• Seal potential is a function of capacity, geometry and integrity of a caprock

• Capacity refers to maximum CO2 column height that can be retained

• Geometry refers to the thickness and lateral extent of the caprock

• Integrity refers to geomechanical properties• Report presents a qualitative assessment

methodology for basin-level screening

• Injection pressure forces CO2 into pores & throats of rock;

• Buoyancy (density difference between CO2 and water multiplied by pressure gradient) causes upward migration

• Column height or seal capacity is determined via MICP and converted to brine/CO2 system using the equation;

Hmax = (Pths – Pthr) ÷ (ρb- ρCO2) 0.433 Where:

Hmax = column height;

Pths = seal threshold pressure;

Pthr = reservoir threshold pressure,

ρb and ρ CO2 are the subsurface densities of water and CO2 respectively

Seal Capacity Determination

Vavra et al 1992

HEIGHT

ABOVE

FWL

(FT)

0

100

200

300

400

500

600

700

800

900

1000

1009080706050403020100

SEAL CAPACITY (Hmax)

WATER SATURATION (Sw)

FWL

Rock “R”

Hmax Pth S - Pth R

Pth S

Rock “S”

Pth R

Young-Laplace Equation

2σ cos θ

Rpc =

Interfacial Tension

Comparison of IFT data, from various authors, highlighting the variability of IFT above ~8 MPa ( Hildenbrand et al., 2004)

CO2 Wettability

Droplet of supercritical CO2, confined by water, on a mineral substrate either mica (proxy for shale) or quartz, showing wetting stages wrt supercritical CO2.

Recent experimental evidence demonstrates that CA can vary from < 10º (qtz) to 116º (mica) depending on lithology, pressure, temperature and salinity

Seal Geometry

• Structural position, thickness and areal extent of caprocks

• Estimated by integrated studies of seismics, core data, well correlations and geological/depositional models

• Caprock thickness (z) does not influence capillary entry pressure, but is critical for continuity in faulted regimes (z > fault throw)

GEOMETRIES OF SEAL FACIES INARJUNA BASIN, INDONESIA

THIC

KN

ES

S (f

t)

LATERAL EXTENT (ft)

2 3 4 5 76

100

10

10 1010 1010101

CHANNEL ABANDON-

MENT MUDS

SHELF CARBONATES

UPPER

LOWER

DELTA FRONT SHALES

DELTA PLAIN

SHALES

PRODELTA SHALES

(Kaldi & Atkinson 1997)

Thickness versus areal extent (upper) and width versus length (lower) of fine grained clasticsediments from various depositional environments

Tidal Flat

Tidal Flat

Data from world-wide modern and ancient analogues. Compiled by (Gibson-Poole et al., 2009 after Root, 2007)

Intraformational Seals (Baffles)CO2

injection well

C. Gibson-Poole, 2003

increase the length / duration of CO2 migration, increasing potential for residual trapping and dissolution

Sandstone reservoirs and intraformational shales

Sandstones

Shales

Numerical flow simulation of CO2injection at Sleipner Field, which has been history matched with time lapse 3D seismic reflection data. Two perpendicular cross-sections of a simulation result are shown (A & B). Intra-formational seals act as barriers to vertical scCO2 migration(van der Meer et al., 2000).

Intraformational Seals (Baffles)?

Seal capacity or geometry (spill point)?

Seal Integrity (Geomechanics)

• Influencing factors:– Lithology– Pre-existing planes of weakness– Regional stress– Induced stress

• Compressible/ductile strata less likely to develop structural permeability

• Can condition models via lab strength tests on samples

Geomechanical Responses of Caprock1. Stress Arching Processes

Early Late

•If caprock is stiff enough, elevated CO2 pressures can lead to an increase in vertical stress directly above the reservoir•In a normal faulting environment this will facilitate reactivation of high angle fault and fracture systems, thereby impacting on integrity.

•Elevated CO2 pressure can lead to poro-elastic feedbacks, resulting in an increase of the minimum horizontal stress at reservoir level.•Because horizontal stress is finite, minimum horizontal stress decreases above and below the reservoir thereby facilitating tensile fracturing.

1. Stress Arching Processes2. Reservoir Stress Path (Pore Pressure/Stress Coupling)

Geomechanical Responses of Caprock

•Injection of “cold” CO2 into a reservoir can impart stresses into both reservoir and caprock

•Given enough time, temperature drop will get transmitted to the caprock resulting in an increase in the tensile stress.

•Caprock integrity is affected by temperature differences, injection rate and heat capacity of well completion materials

1. Stress Arching Processes2. Reservoir Stress Path (Pore Pressure/Stress Coupling)3. Thermo-mechanical Effects During Injection

Preisig & Prevost, 2011

Geomechanical Responses of Caprock

Faults and Fractures

Mst bed

Sst bed

Fault Rock

Fault Zone

Fluid flow

Fault tip

Fault intersection

Fault relayzone

Fluid flow

• Schematic diagram showing zones of fractures (orange polygons) associated with a fault (yellow polygons).

Question:

• Do faults / fractures seal or leak?

Answer:

• Yes!

Juxtaposition Trap

CO2

JUXTAPOSITION:

• Not the only mechanism for fault seal

• Sand on sand may also be sealing via grain sliding, cataclasis, diagenesis, clay smear / shale gouge

• Need to consider fault zone deformation processes (FZDP) along with juxtaposition

CATACLASITE COUNTRY ROCK

CATACLASITE COUNTRY ROCK

Well-lithified cataclasite,Banyula-1, Otway Basin

(Jones & Dewhurst 2000)

Cataclasis

CLAY SMEAR (SHALE GOUGE)

Yielding et al 1997

Clay Smear

Cementation

Cataclasis

Grain Boundary Sliding

OIL COLUMNRETAINED

PORE THROAT RADIUS

North Sea Oil & GasExample(Knipe,1992)

Which Fault Zone Deformation Processes Result in Best Seals?

REACTIVATION OF FAULTS

• Reactivation of faults results in creation of structural permeability networks permitting hydraulic flow

(Sibson, 1996)

Juxtaposition Trap

CO2

Juxtaposition + Reactivation

CO2

Residual Saturation(SgrCO2)

Juxtaposition + Reactivation

CO2

FAULT SEALS FOR CO2 CONFINEMENT

• Where CO2 is trapped by a sealing fault, a cap-rock seal must also be present

• Either the fault itself is acting as a seal or the juxtaposition of rocks across the fault results in sealing

• Fault movement causes leakage along the fault

In Situ Stress

Maximum horizontal stress orientation (σH):– Breakouts, and Drilling Induced Tensile Fractures (DITFs);

(Caliper, Image logs)

σh

σH

σv

King, 2008

Predicting Reactivation Potential (RP)

1.0

0.8

0.6

0.4

0.2

0.0

0.9

0.7

0.5

0.3

0.1

σHmax

030

60

90

120

150180

210

240

300

270

330

RP

Combination of shear and

tensile failure likelihood

StructralPermeability Stereonet:

Planes plottedas poles

Critically oriented

faults strike 120-210ºN

σHmax

Mildren et al, 2000

Geochemistry• Geochemical effects can theoretically

increase or decrease caprock permeability• Long timescale predictions difficult –

reaction kinetics• Heterogeneity within caprock • Buffering capacity of caprock minerals• Report presents 4 case studies:

– laboratory studies and numerical modelling studies in comparison with natural analogues

– Covers typical caprocks such as: shale, limestone, anhydrite and halite

Hydrodynamics

• Differential excess pressures above and below caprock can affect sealing capacity

• Over-pressured aquifers above caprock may control membrane seal capacity

• Over-pressures either side of faults control seal capacity

• Idealised scenarios described – effects of heterogeneity uncertain

Conclusions• Assessment of caprock systems highly site-specific• Seal potential function of capacity, geometry and integrity• Key knowledge gaps identified include:

– Wettability and IFT for water-rock-scCO2 systems– Hydrodynamic effects on membrane seal capacity

during large scale storage– Role of faults / fractures in caprock systems– Caprocks database lacking– Characterisation of regional geomechanical properties

is problematic (e.g. scalar effects from lab tests)– Coupled geochemical / geomechanical processes– Direct monitoring of caprock

• Opportunities in existing/future demo projects?

Thank you

For more information see

www.co2crc.com.au