Stephanie Vialle
Senior Lecturer
Geological storage and sequestration of CO2 in saline aquifers, depleted oil & gas reservoirs and unminable coal seams is one of the most sought after technologies to help mitigate greenhouse gases emissions. Monitoring of CO2 sequestration projects for quantification and assurance of storage security is essential for the commercial deployment of this technology. In seismic monitoring, data are classically interpreted via Gassman's fluid substitution model, which is valid for sigle phase and relatively chemically inert systems. However, many minerals are chemically reactive in a CO2-brine environment, and observations and/or geochemical monitoring from natural analogs, CO2 injection pilot projects and CO2-EOR projects, have confirmed it. Through a combination of laboratory experiments, reactive multi-phase flow modelling and rock physics modelling, the studies below aim at providing new technologies and methodologies to improve 4D seismic monitoring in geochemically reactive systems.
Effects of the reactions of precipitation and dissolution on the transport, electrical and seismic properties of carbonates
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At Insitut de Physique du Globe Paris,
funded by Sclumberger Water Services
My thesis was focused on the use of seismic and non-seismic methods to detect geochemical reactions induced by CO2-rich fluids in limestones as well as permeability-porosity relationships. I combined classical aqueous chemical analyses, experimental rock physics techniques and X-ray tomography to quantify changes in the pore space, porosity and permeability of the rock, and the resulting impact on the electrical formation factor and on the ultrasonic P- and S-wave velocities.
Estaillades carbonate - 3D reconstruction of the dissolved rock frame from X-ray imaging.
Geophysical monitoring of CO2-induced dissolution in carbonates
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At Stanford Rock Physics Laboratory
While at Stanford as a postdoctoral researcher in the Rock Physics group, I worked on time lapse acoustic monitoring in clean and oil-bearing carbonates when they are flooded with CO2-rich water, which induces dissolution of calcite, increase in porosity and loss of strength in the rock frame. Because the current rock physics models that are used to invert the seismic data into rock and fluid properties assume a purely mechanical coupling between the rock frame and the saturating fluid, this study showed they must be adapted to apply to a highly reactive system. My research provided key methods and experimental data needed to revise existing seismic models, allowing us to better image CO2 migration and geochemical reactions in carbonate reservoirs.
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Evolution of a fractured system with a CO2 leak, using reactive transport modeling
With the Stanford Carbon Capture Project
The Carbon Capture Project, Phase 3 (CCP3) is an interdisciplinary research team focused on detection, characterization and mitigation of subsurface CO2 leaks.
I used reactive transport modeling at the reservoir scale to study the geochemical evolution of a fractured caprock (a fault-damage zone system). By introducing a heterogeneous permeability field in the damage zone via numerical upscaling, I found that the geochemical evolution of the system was different, both in time and space, compared to the case of a homogeneous permeability field in the damage zone. The later was how the majority of reservoir-scale models were treating fault zones, possibly leading to erroneous conclusions regarding leakage rates and remediation. A lateral migration of the leak was observed due to precipitation reactions and subsequent changes in porosity and permeability, as well as self-healing of the initially fractured zones.
Vialle et al., 2013 AGU Fall Meeting - Poster
From Benson & Hepple. 2004
Lateral migration and self-healing of a CO2 leak in a fractured caprock due to precipitation reactions.
Rock Physics interpretation of crosswell seismic data constrained by geological and geochemical information - Frio CO2 brine project (Texas)
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With the dept. of Exploration Geophysics, Curtin Uni and Berkeley National Laboratory, USA
PhD of Mohammed Al Hosni
Seismic monitoring performed at the carbon storage pilot site at Frio (Texas) in 2004 showed a large decrease in both P- and S-wave velocities that couldn't be explained by classical rock physics interpretation (pure fluid substitution) nor by pressure increase. Guided by the geochemical monitoring that showed rapid dissolution of calcite and Fe-oxides following CO2-injection, and by rock microstructure analysis, a new rock physics interpretation was proposed: 1) the reservoir rock was interpreted as a poorly consolidated sandstone (i.e. use of the constant cement model) and 2) the loss of rock stiffness was interpreted as cement removal at grain contact.
The amount of cement that needed to be 'removed' in order to explain the decrease in Vp and Vs was in aggreement with that found from an independant reactive transport modelling performed by Sandia National Lab.
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2D vertical cross section of changes in Vp and Vs (left and middle) from cosswell data and interpretation in term of changes in amount of contact cement (right).
Shallow release of CO2 at Otway, Australia
Laboratory study to assess geophysical monitoring and potential groundwater contamination
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With the Center of Exploration Geophysics, Perth and Geoscience Australia
The Otway CO2 site, Australia’s first demonstration project of CO2 geological sequestration, provides the ideal location to complete a field scale investigation for shallow release of CO2, in a near-surface fault. The experience will be particularly relevant to understanding CO2 migration in the overburden and the improving prediction of fluid flow in karstic and faulted near surface environments.
We performed laboratory experiments that examine the chemical and physical behaviour of CO2 gas released into whole cores. The 2 main aspects studied were: the behavior of rock and fluid frequency-dependent electrical resistivities to help calibrate and design the field scale geophysical monitoring, and the chemical evolution of the effluent to asses potential release of metals and contamination of shallow groundwater.
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Results soon to come...
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Photographs showing A - the experimental set-up for the core flooding and B - a close-up of the core holder and of the inline probe for pH and fluid EC monitoring.