Capturing the magic of carbon dioxide: Engaging hands-on demonstrations to explain geological storage

Bureau of Economic Geolog

Atmospheric Tomography as a Tool for Quantification of CO2 Emissions from Potential Surface Leaks: Signal Processing Workflow for a Low Accuracy Sensor Array

AbstractAtmospheric tomography is a monitoring technique that uses an array of sampling sites and a Bayesian inversion technique to simultaneously solve for the location and magnitude of a gaseous emission. Application of the technique to date has relied on air samples being pumped over short distances to a high precision FTIR Spectrometer, which is impractical at larger scales. We have deployed a network of cheaper, less precise sensors during three recent large scale controlled CO2 release experiments; one at the CO2CRC Ginninderra site, one at the CO2CRC Otway Site and another at the Australian Grains Free Air CO2 Enrichment (AGFACE) facility in Horsham, Victoria. The purpose of these deployments was to assess whether an array of independently powered, less precise, less accurate sensors could collect data of sufficient quality to enable application of the atmospheric tomography technique. With careful data manipulation a signal suitable for an inversion study can be seen. A signal processing workflow based on results obtained from the atmospheric array deployed at the CO2CRC Otway experiment is presented

Steroid estrogens in primary and tertiary wastewater treatment plants

The concentrations of two natural estrogens (Estrone (E1) and Estradiol (E2)) and one synthetic progestin (Ethinylestradiol (EE2)) were measured for different unit operations in an advanced sewage treatment plant and in a large coastal enhanced primary sewage treatment plant. The average influent concentration to both plants was similar – 55 and 53 ng/L for E1 and 22 and 12 ng/L for E2 for the advanced and enhanced primary STPs, respectively. The activated sludge process at the advanced STP removed up to 85% and 96% of E1 and E2, respectively. The enhanced primary sewage treatment plant was mostly ineffective at removing the steroids with only 14% of E1 and 5% of E2 being removed during the treatment process. EE2 was not been detected during the study period in the influent or effluent of either STP. The difference in the observed removal between the two plants is primarily linked to plant performance but the extent to which removal of steroid estrogens is due to bacterial metabolism (i.e. the advanced STP) rather than adsorption to the bacterial biomass remains unclear. The poor removal observed for the coastal enhanced primary STP may have implications for the receiving environment in terms of a greater potential for abnormal reproductive systems in marine animals, particularly if discharges are into large bays or harbours where flushing is limited

Fate of Steroid Estrogens in Australian Inland and Coastal Wastewater Treatment Plants

A comparison of estrone (E1), 17b-estradiol (E2) and 17a-ethinylestradiol (EE2) removal at a coastal enhanced primary and inland advanced sewage treatment plant (STP) is reported. The average concentration of estrogens in the raw sewage is similar to reports in other studies. The sequential batch reactor at the advanced STP removed on average 85% of the incoming E1 and 96% of the E2. Further removal was observed during later microfiltration with the estrogen concentration below detection (<0.1 ng.L-1) after reverse osmosis. Some 6% of the influent E1+E2 was removed in the waste activated sludge. The detection of EE2 in the waste activated sludge (0.42 ng.g-1 solids dry weight), undetectable in the raw sewage, suggests that EE2 is resistant to biological treatment in the sequential batch reactor and is primarily removed due to sorption. Little estrogen removal was observed at the enhanced primary with only 7% of E1 and 0% of E2 removed. Low removal is expected based on the degree of estrogens partitioning in the organic fraction given the relatively low solids concentration, but surprisingly, some 43% of E2, 24% of E1 and 100% of EE2 remains associated with the solids fraction in the treated effluent. Further research is necessary to determine whether the low level of estrogen removal for the coastal treatment plant will adversely affect the receiving marine environment

Quantifying CO2 leak rates in aquatic environments

The Daylesford region of Victoria (Australia), is a region of natural CO2 seepage. Small bubble streams of CO2 are released into ephemeral river beds proximal to mineral springs that contain high dissolved CO2 content. We study four sites of CO2 degassing to (i) establish the characteristics of CO2 seepage caused by transport to surface of CO2-rich water, (ii) provide an estimate of CO2 flux in the region, and (iii) investigate seasonal effects on CO2 seepage. We observe that bubbling behavior varies considerably between sites, including the number and distribution of bubbling points, and bubble stream the continuity. Total CO2 seep rates at each site were low (< 20 kg/d) but varied substantially between different sites. There were no obvious indicators of total emission rate; the bubble density or other characteristics at the highest emission seep were not remarkably different to the smaller seeps. We find that the total CO2 emission varies inconsistently with season, with some seep rates increasing and other decreasing in the dry season when water levels are lower. We find there are challenges in quantifying the total gas leakage at sites of highly localized and intermittent degassing. Our work has implications for detecting and quantifying leaks from engineered CO2 storage sites which emerge in aqueous environments, which could be these are marine or terrestrial (lakes or rivers)

Evaluating the Economic Potential for Geological Hydrogen Storage in Australia

Australia has ambitions to become a major global hydrogen producer by 2030. The establishment of Australia’s and the world’s hydrogen economy, however, will depend upon the availability of affordable and reliable hydrogen storage. Geological hydrogen storage is a practical solution for large scale storage requirements ensuring hydrogen supply can always meet demand, and excess renewable electricity can be stored for later use, improving electricity network reliability. Hosting thick, underground halite (salt) deposits and an abundance of onshore depleted gas fields, Australia is well placed to take advantage of geological hydrogen storage options to support its ambition of building a global hydrogen hub export industry. Using the Bluecap modelling software, we identify regions in Australia that are potentially profitable for large scale hydrogen production and storage. We use the results of this work to suggest high-potential regions for hydrogen development, supporting policymaker and investor decisions on the locations of new infrastructure and hydrogen projects in Australia

Bayesian atmospheric tomography for detection and quantification of methane emissions : application to data from the 2015 Ginninderra release experiment

Detection and quantification of greenhouse-gas emissions is important for both compliance and environment conservation. However, despite several decades of active research, it remains predominantly an open problem, largely due to model errors and assumptions that appear at each stage of the inversion processing chain. In 2015, a controlled-release experiment headed by Geoscience Australia was carried out at the Ginninderra Controlled Release Facility, and a variety of instruments and methods were employed for quantifying the release rates of methane and carbon dioxide from a point source. This paper proposes a fully Bayesian approach to atmospheric tomography for inferring the methane emission rate of this point source using data collected during the experiment from both point-and path-sampling instruments. The Bayesian framework is designed to account for uncertainty in the parameterisations of measurements, the meteorological data, and the atmospheric model itself when performing inversion using Markov chain Monte Carlo (MCMC). We apply our framework to all instrument groups using measurements from two release-rate periods. We show that the inversion framework is robust to instrument type and meteorological conditions. From all the inversions we conducted across the different instrument groups and release-rate periods, our worst-case median emission rate estimate was within 36% of the true emission rate. Further, in the worst case, the closest limit of the 95% credible interval to the true emission rate was within 11% of this true value

Could faults provide conduits for fluid escape? New field data in the vicinity of the Otway International Test Centre

Introduction It is well known that faults affect fluid movement within the subsurface and this can have a host of implications for the measurement, monitoring, and verification of subsurface technologies (e.g., carbon capture and storage (CCS), energy storage, geothermal energy, and radioactive waste disposal). Faults are an important control on the escape of fluids from depth (e.g., Dockrill and Shipton, 2010). It is therefore important to consider the potential effect of faults in the shallow overburden to any future CCS sites. However, there is very little data on fault architecture in shallow sediments, and consequently their effect on fluid flow is far less well understood than flow through faults at hydrocarbon reservoir depths. In early 2024, a novel field trial injection will be conducted at the CO2CRC Otway International Test Centre (OITC), located in southern Victoria, Australia (Figure 1). The injection will involve a small volume of CO2 (~10 t) being injected into the Brumbys Fault, which will be monitored using various surface and downhole monitoring techniques (Tenthorey et al., 2022), to provide data on the transport of CO2 through shallow faults. The 1.2km long Brumbys Fault is hosted in the Miocene Port Campbell Limestone (PCL) carbonate sequence that outcrops across southern Victoria, with varying thickness from ~30m to 270m (Radke et al., 2022). Brumbys Fault has been interpreted as a strike-slip fault, due to its near-vertical dip (~80°), small throw (2-4m), and favorable orientation to the present-day stress (~30° from the maximum horizontal stress) (Feitz et al., 2018). However, there are no convincing surface markers indicating horizontal displacement. To reduce the uncertainty regarding the fault kinematics, we attempt to reconcile the styles of faulting observed in nearby field exposures with the observations made at the OITC boreholes. Method The Port Campbell Limestone is exposed in coastal cliffs, from Childers Cove in the west (38.489101, 142.672736) to Gibson Beach in the east (-38.674070, 143.117769) and inland in Kurdeez quarry (Figure 1). Access to the cliff faces is limited due to the lack of access points and tides, precluding the collection of detailed field data therefore most field observations were made from adjacent cliffs and tourist lookout spots where available. Results Reverse faulting (1-2m throw) was observed along coastal outcrops (Figure 2) in the eastern portion of field area: outcrops examined west of Port Campbell did not exhibit any faulting. Reverse features had a strike ~50-60°, which is consistent with the maximum horizontal stress direction (~142°). There is some evidence of large vertical fractures (10s m vertical extent) that could be associated with strike slip movement, but horizontal offset could not be seen in cliff and quarry outcrops due to limitations is 3D accessibility of features. These features had a strike of either ~105-110° or ~170-175°. Smaller, more localized vertical and sub-vertical fractures striking ~175° are confined to individual layers within the PCL, highlighting the variation in mechanical properties within different sections of the PCL sequence. At Kurdeez quarry, the PCL is significantly less consolidated compared to the coastal outcrops, which is similar to the rock core retrieved from the Brumbys-1, 2 and 3 wells. Spatial variations in diagenetic or depositional history have influenced the mechanical properties of the PCL and may in turn have influenced the fault formation. Conclusions There is a spatial variation in the location and type of faulting in the study area: eastern coastal areas host reverse faulting, whereas western coastal areas and inland areas lack evidence of reverse faulting and are unconsolidated. The PCL is much thicker to the west and north (where it reaches its maximum thickness of ~270m thick), which may explain this spatial variation in deformation style. Further work on the interpretation and characterisation of Brumbys Fault will be necessary before any injection experiment to ensure the fault geometry and fluid flow implications are fully understood

Continuous monitoring of natural CO2 emissions near Rome: lessons for low-level CO2 leakage detection

Continuous monitoring has been carried out at a fluvial flood-plain site near Rome for over a year. There is a mix of biogenic CO2 and deep geogenic CO2 at the site at relatively low concentrations and fluxes compared with other natural CO2 seepage sites studied previously. Factors such as temperature and soil moisture clearly affect the CO2 concentration and flux and seasonal and diurnal influences are apparent. Statistical approaches are being used to try to define these relationships and separate out the two gas components, which would be necessary in any quantification of leakage from CO2 storage

CSIRO In-Situ Lab : a multi-pronged approach to surface gas and groundwater monitoring at geological CO2 storage sites

In February 2019, at the CSIRO In-Situ Laboratory CCS project, a test was conducted where 38 t of gaseous CO2 were injected over 5 days into a fault zone at a depth of approximately 340 m. As a release test, this project enabled the testing and validation of surface and shallow well monitoring strategies at intermediate depths (i.e. depths much deeper than previous release projects and shallower than reservoirs used for CO2 storage). One of the aims of this project is to understand how CO2 would behave at intermediate depths if it did migrate from deeper depths (i.e. from a storage reservoir); the CO2 was not intended to migrate to the shallow subsurface or to surface/atmosphere. To verify that the injected CO2 remained in the subsurface, and to comply with environmental performance requirements on site, a comprehensive surface gas and groundwater monitoring program was conducted. The monitoring strategy was designed such that any leakage(s) to the surface of injected CO2 would be detected, mapped and, ultimately, quantified. The surface air monitoring program was comprised of three different but complementary approaches allowing data to be efficiently collected over different spatial and temporal scales. These approaches included continuous soil-gas chamber measurements at fixed locations, periodic soil-gas chamber measurements on gridded locations and near-surface atmospheric measurements on a mobile platform. The surface air monitoring approaches gave self-consistent results and reduced the risk of “false negative” test results. The only anomalous CO2 detected at the surface flowed from the observation well and could be directly attributed to a breach in the well casing at the injection depth providing a conduit for CO2/water to rise to the surface. Groundwater monitoring program revealed no impact on the groundwater resources attributable to the carbon injection project. Based on this work, we demonstrate that this multi-pronged monitoring strategy can be utilized to minimize the overall resources devoted to monitoring by increasing the number of monitoring approaches and diminishing the resources devoted to each technique. By maximizing the effectiveness of each element of the monitoring program, a cost-efficient and robust monitoring strategy capable of early leak detection and attribution of any leaking CO2 can be achieved