Final blog from by Sasha Serno of the University of Edinburgh on the UKCCSRC Call 2 project Quantifying Residual and Dissolution Trapping in the CO2CRC Otway Injection Site (PI: Stuart Gilfillan)
Our project “Quantifying Residual and Dissolution Trapping in the CO2CRC Otway Injection Site”, funded by UKCCSRC Call 2, aimed to study the application of oxygen isotopes and noble gases (xenon and krypton), collected during the residual saturation test of the CO2CRC Otway Stage 2B Extension project, to monitor residual trapping of CO2. This is the first study of its kind to use oxygen isotopes in a single-well field experiment to reconstruct residual trapping levels. The Otway CO2 test injection site provides CCS researchers with the ideal conditions to test monitoring techniques.
Following our trip to Australia in December 2014 to collect all necessary water and CO2 samples from the field project at Otway, we spend months with the complex data interpretation of the collected stable isotope and noble gas geochemical data, working together with our Australian, US and Canadian colleagues involved in the field project. This provided us with a great opportunity to build closer bonds with different CCS groups in these countries for continuous CCS research in the following years. Dr. Sascha Serno, the postdoctoral researcher working on the Call 2 project, further spent 4 weeks at CSIRO Energy in Melbourne in April/May 2015 to work more closely together with the Australian colleagues from CSIRO and CO2CRC, and to get some hands-on training and experience in reservoir flow simulations using PetraSim. This trip was funded through the UKCCSRC International Exchange Fund. Throughout 2015, we further presented our preliminary findings from the project during multiple conferences, including the IEAGHG Monitoring Network in Berkeley, California, in June 2015, the SCCS Conference in Edinburgh in October 2015, and during seminar talks at CSIRO Energy, CO2CRC, Imperial College London and the University of Edinburgh.
In December 2015, we finished up our interpretation and writing of the oxygen isotope data from the Otway Stage 2B Extension project and submitted it for publication at the International Journal of Greenhouse Gas Control. The manuscript is now published. We found convincing results of an oxygen isotope shift in the reservoir waters in contact with residually trapped CO2 in the subsurface, compared to baseline conditions with no trapped free-phase CO2. This shift in the water isotope signature can be used to estimate residual trapping levels using simple geochemical modelling approaches defined by Dr. Gareth Johnson. Our trapping levels are similar to independent estimates based on pulsed neutron logging and simulations of the noble gas data injection and recovery, which were conducted by our colleagues from CSIRO Energy, with our help in the geochemical data interpretation. The manuscript describing the noble gas data is currently under review with the International Journal of Greenhouse Gas Control.
In 2016, we focussed on the further dissemination of the oxygen isotope data during conferences, including the UKCCSRC Biannual in Edinburgh, EGU General Assembly in Vienna and GHGT in Lausanne, to disseminate the success and way of application of this relatively inexpensive monitoring tool to be used in future CO2 injection projects. We further studied the application of oxygen isotope data in quantifying reservoir–scale CO2 pore-space saturation during a CO2 injection field project, and put together a comprehensive collection of oxygen isotope data from various CO2 injection projects and drafted a review manuscript that describes the observations based on oxygen isotope ratios and how this monitoring technique can be improved in future field experiments. This manuscript is currently under review with the International Journal of Greenhouse Gas Control. The interpretation of the field data from the Otway Stage 2B Extension project resulted in some interesting, but also puzzling new research questions. In particular, we observed some trends in the oxygen isotope shifts in the reservoir water samples collected from the different distances from the wellbore that were hard to explain initially. We therefore conducted a relatively simple laboratory experiment to study the oxygen isotope behaviour in reservoir water and CO2 in a field setting characterised by the injection of water/CO2 and the back-production of the same through the same well. This has not been conducted before, and therefore our understanding of the geochemical dynamics in such a field setting is very limited, but this understanding is crucial for the application of this tool in future single-well CO2 injection projects. The data analysis is still underway for this laboratory experiment, with the data interpretation and writing stages early in 2017.
Finally, we would like to thank UKCCSRC for the generous funding of our project. We substantially advanced the understanding in the application of oxygen isotope ratios and noble gases in studying CO2 pore-space saturation in CO2 injection projects. However, we also discovered some interesting knowledge gaps that can be studied in laboratory, field and modelling studies. In particular, the project provided us with the ideal setting to build strong relationships with research partners from CO2CRC, CSIRO and the University of Melbourne, as well as from research institutions in the UK, USA and Canada to continue Edinburgh-based geochemical CCS research in the years to come. Particularly, we plan to develop an on-side continuous geochemical approach for stable and noble gas isotopes to be applied in upcoming field projects in Australia and elsewhere to monitor hourly changes in the isotope signature of reservoir water and CO2 produced from observations wells.