Linda Stalker

Safe storage and effective monitoring of CO2 in depleted gas fields

Carbon capture and storage (CCS) is vital to reduce CO2 emissions to the atmosphere, potentially providing 20% of the needed reductions in global emissions. Research and demonstration projects are important to increase scientific understanding of CCS, and making processes and results widely available helps to reduce public concerns, which may otherwise block this technology. The Otway Project has provided verification of the underlying science of CO2 storage in a depleted gas field, and shows that the support of all stakeholders can be earned and retained. Quantitative verification of long-term storage has been demonstrated. A direct measurement of storage efficiency has been made, confirming that CO2 storage in depleted gas fields can be safe and effective, and that these structures could store globally significant amounts of CO2.

South West Hub: a carbon capture and storage project

The South West CO2 Geosequestration Hub (the South West Hub) is located in South West Western Australia in proximity to industrialised regions around Kwinana, Kemerton, and coal mining and power production facilities around Collie. Recognition that there is a potentially suitable geosequestration site in the region near extensive emission sources led to the formation of the South West Hub and its submission as a potential Flagship under the Australian Federal Clean Energy Initiative (CEI). An area with geosequestration potential was identified based on data from years of active research in the region to investigate oil and gas potential, ground-water resources and more recently for geothermal energy potential and now carbon storage. Three interesting factors stand out regarding this site: (1) the storage site relies primarily on residual and dissolution trapping, (2) some of the CO2 will be sequestered by mineralisation during the amelioration of bauxite residue from some nearby alumina plants, and (3) the subsurface storage area can be tested at a relatively early stage by accessing significant pilot-scale quantities of high-purity CO2 from existing industry in the Kwinana area. CO2 is already being captured and vented at a site in Kwinana, and a proposed pipeline will transport the CO2 to the alumina plants with the remainder of the gas used for a pilot-scale test. The upfront capital costs are therefore reduced to the pipeline cost rather than for a full-scale capture-ready power plant. In preparation for an investment decision (to drill a new data well addressing the main criteria for characterising carbon storage potential of the proposed Lesueur site) a series of studies have increased the understanding of the geology of the area. Modelling studies suggest that up to 6.4 million tonnes per annum could be stored in the Triassic aged Lesueur Sandstone, with total capacity estimates of 200–260 million tonnes of CO2 over the lifetime of the project. This paper primarily discusses the evolution of the geological understanding of the Lesueur Sandstone and associated formations in and around the Harvey Ridge structure, which falls within the Lesueur study area, as well as how the Collie coal users and producers and other local industries and government have become engaged in the project. Recent activities in the project have included seismic data acquisition and the drilling, coring and logging of a data well that will allow significant reductions in geological uncertainties for the project.

A mid-infrared sensor for the determination of perfluorocarbon-based compounds in aquatic systems for geosequestration purposes

Perfluorocarbon (PFC) compounds have been used as chemical tracer molecules to understand the movement of supercritical carbon dioxide for geosequestration monitoring and verification purposes. A commonly used method for detecting PFCs involves the collection of a sample from either soil-gas or the atmosphere via carbon-based sorbents which are then analyzed in a laboratory. However, PFC analysis in aquatic environments is neglected and this is an issue that needs to be considered since the PFC is likely to undergo permeation through the overlying water formations. This paper presents for the first time an innovative analytical method for the trace level in situ detection of PFCs in water. It reports on the development of a sensor based on mid-infrared attenuated total reflection (MIR-ATR) spectroscopy for determining the concentration of perfluoromethylcyclohexane (PMCH) and perfluoro-1,3-dimethylcyclohexane (PDCH) in aquatic systems. The sensor comprises a zinc selenide waveguide with the surface modified by a thin polymer film. The sensitivity of this device was investigated as a function of polymer type, coating thickness, and solution flow rates. The limit of detection (LOD) was determined to be 23 ppb and 79 ppb for PMCH and PDCH, respectively when using a 5 μm thick polyisobutylene (PIB) coated waveguide. This study has shown that the MIR-ATR sensor can be used to directly quantify PFC-based chemical tracer compounds in water over the 20-400 ppb concentration range.

Organic acid concentration thresholds for ageing of carbonate minerals: Implications for CO2 trapping/storage

HYPOTHESIS CO2 geological storage (CGS) involves different mechanisms which can store millions of tonnes of CO2 per year in depleted hydrocarbon reservoirs and deep saline aquifers. But their storage capacity is influenced by the presence of different carboxylic compounds in the reservoir. These molecules strongly affect the water wetness of the rock, which has a dramatic impact on storage capacities and containment security. However, precise understanding of how these carboxylic acids influence the rocks CO2-wettability is lacking. EXPERIMENTS We thus systematically analysed these relationships as a function of pressure, temperature, storage depth and organic acid concentrations. A particular focus was on identifying organic acid concentration thresholds above which storage efficiency may get influenced significantly. FINDINGS These thresholds (defined for structural trapping as a water contact angle θ > 90°; and for capillary trapping when primary drainage is unaffected, i.e. θ > 50°) were very low for structural trapping (∼10-3-10-7 M organic acid concentration Corganic) and extremely low for capillary trapping (10-7 M to below 10-10 M Corganic). Since minute organic acid concentrations are always present in deep saline aquifers and certainly in depleted hydrocarbon reservoirs, significantly lower storage capacities and containment security than previously thought can be predicted in carbonate reservoirs, and reservoir-scale models and evaluation schemes need to account for these effects to de-risk CGS projects.

Bursting bubbles: can experiments and analogues help stakeholders and the public visualise risks?

Laboratory experiments, natural analogues and pilot projects have been fundamental in developing scientific understanding of risk and uncertainty from georesource exploration. International research into CO2 and CH4 leakage provide scientific understanding of potential leakage styles, rates and environmental impacts. However, the value of these experiments as a communication tool for stakeholders and the wider public is often overlooked in the form of visual information and comparisons. Quantifiable laboratory experiments, measurement of gas at natural springs or controlled release of CO2 (e.g. Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbon Storage Project (QICS)) raise awareness and commitment to understanding environmental impacts and geological complexities. Visuals can greatly facilitate communication, and research into public understanding of the subsurface demonstrates that quality and scale of schematics can affect perceived risk. Here we consider how public perception of subsurface activities could be shaped by relevant and applicable research that shares accessible and visually engaging information. Could images showing bubbles of seeping gas, or showcasing monitoring methods and capabilities, help to contextualise risks and geoscientific concepts and shape opinions? Can these materials aid dialogue between the wider scientific community, publics and stakeholders? We propose that future projects could improve dialogue through use of context-appropriate visuals to enhance dialogue on risks, impacts and monitoring of subsurface engineering technologies.

Preliminary Analysis of Containment Integrity for Geological Storage of CO2 at the South West Hub Project, Western Australia

The Mandurah Terrace in the onshore Perth Basin was proposed as a suitable site for CO2 injection. Prior investigations in the area indicate that faults affect the target storage reservoir and shale barriers. Changes in the pore pressure and stress field induced by fluid injection could alter the containment integrity by either exceeding fault capillary resistance or by triggering slip on pre-existing faults. The capillary properties of faults have been assessed using the Shale Gouge Ratio predictive algorithm which can assess the maximum fluid column height trapped by a fault without leaking. Three different scenarios were investigated, representing different juxtaposition geometries. In the south of the area, potential spots for local up and across fault fluid migration are noted. The relationship between the modelled faults and the present-day stress field has been investigated to define critically stressed fault segments most at risk of reactivation resulting from pore-pressure build-up due to injection. The likelihood of fault reactivation is low in the current day stress field with pore pressures required equivalent to a CO2 column exceeding 1000m. Preliminary geomechanical modelling also shows no likelihood of fault reactivation and potential ground uplifts of less than two centimetres at the surface.