COSMOS - CO2 Storage, Monitoring and Safety Technology ...

COSMOS - CO2 Storage, Monitoring and Safety Technology
Subprojekt 3: Cap Rock Integrity
(Untersuchung der Dichtheit von Hutgesteinsformationen von Gas- und Fluidspeichern für
die Einlagerung von CO 2 )
The success of
geological CO 2
storage projects
depends largely
on the ability to
monitor the state
of the reservoir
during and after
the CO 2 injection,
e.g. in terms of
fluid saturation,
pore pressure,
and cap rock
integrity. This is
essential for longterm
reservoir
management and
risk assessment.
Scenario for the potential reduction of cap rock integrity
The research refers to the first German On-Shore Pilot project for the geological storage of
CO 2 in Ketzin.
The quantitative interpretation of geoelectrical and geophysical field data is supported by
an extensive experimental program in the laboratory under in-situ pressure and
temperature conditions covering fluid properties as well as fluid-rock and fluid-cement
interactions.
Work packages:
• Wellbore Integrity
• Reservoir Monitoring
• Cap Rock Integrity

Project Data
This work has been part (SP 3) of the
Joint Research Project:
CO2 Storage, Monitoring and Safety Technology - COSMOS
Sponsored by the Federal Ministry of Education and Research (BMBF)
in the framework of the special research program “Geotechnologies“
under ident. no. 03G0630C
Project partners:
• GeoForschungsZentrum Potsdam (GFZ, coordinator)
• DBI - Gastechnologisches Institut gGmbH, Freiberg
• Vattenfall Europe AG
• Karlsruhe Institute of Technology (KIT) – Institute of Soil Mechanics and Rock
Mechanics (IBF), Institute of Mineralogy and Geochemistry (IMF),
Forschungszentrum Umwelt (FZU), Institute of Technical Chemistry (ITC-WGT)
• RWE Power, Essen
Term period: 01.04.2005 - 31.03.2008
Contributions from IBF Researchers:
• Karl Balthasar
• Gerd Gudehus
• Thomas Mutschler
• Sascha Rübel
• Theodoros Triantafyllidis

Project Scope and Methodology
Aims of the investigation of the cap rock properties above the Ketzin CO 2 storage
reservoir:
• Definition of suitable criteria to avoid any loss of cap rock integrity
• Proof that these criteria are satisfied in the case of Ketzin
• Development of „Best Practises“ for
the characterization of cap rock in the
framework of CO 2 storage reservoir
exploration
IBF focus and work packages:
• Laboratory tests in various scales for
the determination of the
geomechanic properties of the cap
rock
• Experimental determination of
geohydraulic parameters of cap
rock, including their modification by
new or reactivated fractures
Cap rock samples from Ketzin
• Numerical modelling of realistic
deformations in the system reservoir-cap rock using the material properties above.

Geomechanic Properties
Strength and deformation parameters were measured in:
• A novel triaxial apparatus of RWE power with high-resolution measurement of volume
change, in the construction of which the IBF was significantly involved and which was
loaned to IBF for these investigations,
• A large-scale triaxial cell for samples of 600 mm diameter and 1200 mm length,
• Uni-axial compression with real sample deformation monitoring by DMS.
The reservoir
formation in
Ketzin is
sandstone and
the cap rock a
Keuper claystone
with visco-elastic
behaviour. As
long as cores
from Ketzin were
not yet available,
experiments
were also
performed
• on artificial
compacted
bentonite
samples
Triaxial apparatus with high-resolution volume monitoring
Bentonite sample, Ketzin small-scall sample, claystone larg-scale sample after failure
• on a similar Keuper claystone from Southern Germany.
Comparison of results from small-sized and large-sized samples shows no significant
scale effects.

Permeability Tests
Test devices for geohydraulic properties consisted of
• a special permeability cell, in which the sample was glued into a metal ring and fluid or
gas could be penetrated from both sides, thus allowing a “permeation”, an
“impregnation” and an “exsiccator” operation mode,
• the permeability measuring periphery
• a punching tool to force circular shear planes in a sample
Permeability apparatus: flow principle, view and sample with punched circular shear plane
The permeability of undisturbed cap rock samples is below 10 -16 m² . It can be much less
depending on microfractures. CO 2 percolation leads to an increase or decrease.
Responsible opposed reasons are the precipitation of Halit and Anhydrite, clogging the
pore volume, and the advancing desiccation of the sample.
Moderate CO 2 differential pressures seem to have no influence on permeability. With
forced shear zones, the permeability is three magnitudes higher, but constant during
percolation. Self-healing of fractures has been observed in some cases.

Finite-Elemente Simulations
A finite element model was derived from the geological model and based on the
parameters measured in the lab. Formation inclinations were variated
Results show, that the deformation rate reaches its maximum in vertical direction near the
borehole about one year of operation and falls decades below the critical rates in the cap
rock.
This means that the cap rock integrity is proven, the system safey rises after the end of
CO 2 injection. Self-healing of open fractures and auto-inhibition effects may be expected.
Axisymmetric FE model, principle strain rates in the cap rock formation