eScript used in geosequestration project
Plan showing a small plume of injected carbon dioxide (green-blue dot) at a depth of 1.4km underground. Dr Andrea Codd’s objective has been to find the plume using eScript simulations, since it is impossible for humans to see where the plume is injected, and how it infills porous rock from Earth’s surface. Image: Dr Andrea Codd
Injecting compressed carbon dioxide gas (C02) deep underground in a process called geosequestration could potentially be one approach to reducing it in the atmosphere. It is already being implemented in several countries including Germany, USA and Canada; and investigated at CO2CRC’s Otway research facility, Australia’s first demonstration of the deep geological storage of CO2.
An extremely important aspect of geosequestration is monitoring the injected CO2 to ensure that it stays within the porous rock zone as anticipated. Dr Andrea Codd and her team from The University of Queensland have turned their expertise and eScript code to simulate how supercritical CO2 fluid infills porous rock space at the CO2CRC project and model the geophysical signatures it creates.
NCRIS-enabled eScript code, developed by AuScope’s Simulation, Analysis and Modelling team based at The University of Queensland, has been an integral part of a new workflow to monitor injection of CO2 at CO2CRC’s Otway research facility, which has been operational since 2003. Essentially, it has helped the CO2CRC research team understand how to monitor injection projects using gravity and electrical sensors.
Geosequestration involves capturing and burying carbon dioxide from coal-fired power station's chimney flue, then separating, compressing and transporting it to its burial site—often depleted oil or gas wells. The compressed gaseous CO2 is then further compressed into supercritical CO2 before it is pumped more than 1 kilometre underground where it is trapped by a thick layer of clay or some other plug to prevent it leaking out in a porous rock called an aquifer. Learn more about this approach. Image: CO2CRC
Andrea was funded by the Carbon Capture and Storage Research Development and Demonstration Fund (CCSRDDF) to help determine where gravity and electrical sensors could be placed to detect differences to gravity, electrical potential and electrical field in order to devise plausible monitoring strategies.
eScript’s role in this project was to determine if‚ using measurement changes only — the plume could be detected using a process called inversion. These methods use limited localised data, in this case, gravity differences and changes to electrical potential at a small number of locations, to predict properties encompassing the entire burial site.
Dr Andrea Codd explains that outcomes from inversion are not exact, as the number of measurements is much less than the number of unknowns:
“Inversion solutions are just the best possible solution given specific restrictions and assumptions.”
Prof Stephan Matthai and his team from the University of Melbourne produced a detailed ground map incorporating rock properties, layers and faults. Next, they ran simulations of supercritical CO2 fluid injected into an aquifer layer predicting plume evolution. With these results combined, Andrea was then able to use eScript to determine the impact of the plume on rock density and electrical conductivity.
The team found that changes in electrical conductivity could be used to find the plume when the plume was small, and for larger plumes, density changes associated with the plume could be identified in the gravity field.
Schematic cross section showing the 0.9Mt CO2 plume within the aquifer. The white line is the 10% saturation contour of the actual plume and the black line is the 10% saturation contour from the electrical resistivity (top) and gravity (bottom) inversions. Colours show the inversion saturation levels throughout the plume. Dr Andrea Codd
Dr Andrea Codd comments on this project and next steps:
“Inversion methods are an excellent way of looking beneath the ground and are clearly more reliable if they incorporate extensive and detailed ground models demonstrated in this project. Next, our team will focus on developing new inversion methods that are faster and can solve bigger problems using gravity, magnetotelluric and seismic data.”
Andrea would like to thank Prof Stephan Matthai from the University of Melbourne who ran the simulations in this project using his code, Australian Subsurface Carbon Sequestration Simulator (ASCSS), and As Prof Lutz Gross from The University of Queensland and the CO2CRC team for project support.
AUTHORS
By Dr Andrea Codd (The University of Queensland) and Jo Condon (AuScope)
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For information about this story,
please email Dr Andrea Codd