Dr Sascha Serno, PDRA, University of Edinburgh: In December 2014, three researchers from SCCS – Stuart Gilfillan, Gareth Johnson and myself – travelled halfway around the world to Australia with the help of UKCCSRC Call 2 funding to participate in, and co-lead, the Otway 2B extension project conducted at the CO2CRC Otway CO₂ injection site south-west of Melbourne.

CO2CRC is one of the world-leading CCS research organisations. Their Otway test site located in the rolling cow pastures of the Otway Basin and just off the spectacular coastal part of the Great Ocean Road was established in 2003 and is one of only a handful of single-well CO₂ test injection sites in the world. This test site provides CCS researchers with the ideal conditions to run monitoring experiments to demonstrate that CCS is a technically and environmentally safe way to make deep cuts into CO₂ emissions from fossil fuel combustion.

U-tube pic
Gareth (front) and Sascha (back) collecting a sample using the U-tube system
The Otway 2B extension aims to find out how much CO₂ is securely locked away in the subsurface using geochemical monitoring. The two most common CO₂ storage mechanisms are residual and solubility trapping. Residual trapping occurs when CO₂ is locked away in individual and dead-end spaces between rock grains, similar to how air is trapped in a sponge, while solubility trapping refers to CO₂ dissolved into fluids that fill the pores between rock grains, in the same manner as CO₂ is dissolved into water to make it fizzy.

Few research studies so far have found out exactly how much CO₂ is stored by residual and solubility trapping across an entire storage site. Hence, there is a need to develop a reliable means to do this for future industrial-scale storage. The Otway 2B extension project is built on findings from the first successful experimental programme focused on determining residual trapping at the site in mid-2011. In direct collaboration with CO2CRC, the role of SCCS in the project is to use noble gas tracer injection and recovery to determine residual trapping levels, and to apply independent stable oxygen isotope measurements to quantify the amount of CO₂ retained in the reservoir by solubility trapping.

The surface layout at the CO2CRC Otway Project site. The CRC-2 injection wellhead is left of centre, the white CO₂ storage tank is at right and water pipes are in the foreground. Water storage tanks are out of frame to the right. Image: Lincoln Paterson
We were lucky enough to be in Australia for three weeks and worked at the Otway site for two of those weeks. In the first week, the team of 10 scientists from five different countries injected formation water including known amounts of the noble gases (Xenon and Krypton) into the Paaratte Formation through the CO₂ injection well to characterise the noble gas behaviour in the reservoir when no CO₂ is present. The second part followed an interval of pure CO₂ and then CO₂-saturated brine injection into the reservoir. We injected CO₂-saturated formation water with Xenon and Krypton for the final residual saturation test. This was an around-the-clock operation and the on-site scientific team was split up into day and night shifts (from 7am to 7pm, and then from 7pm to 7am). Two scientists per shift, including Gareth and Sascha, were located at the injection well to collect water and gas samples at in-situ pressure from the formation using a U-tube system, with Scottish autumn-like temperatures and with poisonous spiders and snakes for company. The three other scientists from each shift, including Stuart, had the luxury of working in a heated container to measure noble gas tracer concentrations on-site and enjoying the semi-working Australian Wi-Fi. As a result of good planning, great organisational leadership by Dr Chris Boreham from Geoscience Australia and Mr Rajindar Singh from CO2CRC and excellent collaboration between the different international scientists and field operators in the shifts, the field measurements were very successful and recovered a significant portion of the injected tracers.

The geochemical interpretation and numerical simulation of the field data from the Otway 2B extension campaign, in close collaboration with our colleagues from CO2CRC and other research institutions in Australia, will provide us with estimates of the levels of residual and solubility trapping at the Otway site. The stay at the Otway site was an ideal opportunity to further strengthen existing research collaborations between the UK and Australian CCS communities, which will be beneficial in future collaborative projects. CO2CRC secured funding for CCS projects until 2020 from the Australian Government, and new monitoring experiments at the Otway site are already planned for the upcoming years. SCCS hopes to be an active and leading part during these field campaigns.

otway schematic stage2 media
A schematic diagram of the CO2CRC Otway Project Stage 2. CO₂ is produced from the Buttress-1 well on left and injected back into the Paaratte Formation at a depth of around 1400 m at the CRC-2 well. Image: CO2CRC
More information about CO2CRC's work

Further details about the Otway Project

Controls of natural CO₂ storage and leakage in the Otway Basin

For the time in between our stays at the Otway site, we hit the road and drove several hundreds of kilometres to collect gas and water samples from different gas fields and mineral springs in the Otway Basin for a geochemical investigation into the controls of natural CO₂ storage and leakage. Studying the subsurface storage mechanisms of natural CO₂ for millions of years is essential for reassurance of planned storage projects.

Naturally occurring geological faults present one of the key uncertainties in underground CO₂ storage. Faults can provide potential pathways for the leakage of CO₂ to shallow depths. The Otway Basin in south-east Australia contains many natural gas discoveries with CO₂ concentrations >5%, with several almost pure natural CO₂ fields. The gas reservoirs are generally fault bounded traps, which were discovered during exploration drilling operations for hydrocarbons. Significantly, very different gas compositions are often found in structures, which are located adjacent to each other in the basin. The CO₂ has been shown to be of magmatic origin and it is believed that the timing of CO₂ injection varies across the basin corresponding to recent volcanism. In addition to the natural gas fields, CO₂-rich spring waters emanate at the ground surface to the north of the basin in the Daylesford-Hepburn Springs region. Few studies have focused on geochemically investigating the gas compositions in these regions, and the exact source of the gases for both the gas fields and mineral springs is still uncertain. Our fieldtrip was the first part of a longer-term, EPSRC-funded PhD project to provide a detailed understanding of the controls on CO₂ and methane storage and leakage in the Otway Basin.

Next to the collection of gas and water samples from different gas fields in the Otway Basin and natural mineral springs around Daylesford, this road trip in one of the most "exciting" landscapes Australia has to offer provided us with the opportunity to enjoy typical Australian tourist experiences, including climbing mountains with glorious names like Mount Abrupt, enjoying some cricket action at the MCG, learning more about the excellent local brewing skills, and getting to know some special local inhabitants by almost running them over, including koalas, kangaroos and wallabies.

In summary, our successful fieldtrip provides us with an excellent set of field data that will keep us busy for some time. We established strong research collaborations with our colleagues from different Australian research institutions and organisations will hopefully provide opportunities for scientists from SCCS to be involved in monitoring projects organised by CO2CRC in Australia in the future. We would also like to use the opportunity to thank UKCCSRC for providing funding for this fieldtrip.

Sutton Spring sampling
Gareth and Sascha collecting a gas sample from the Sutton No. 1 Spring in Daylesford, Victoria

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