Final Report from Call 2 Project: Quantifying Residual and Dissolution Trapping in the CO₂CRC Otway Injection Site

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.

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.

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