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Overview

As part of the National CO₂ Infrastructure Plan (NCIP), the Vlaming Sub-basin CO₂ Storage Section is providing pre-competitive data and information on the prospectivity of this basin for the long-term geological storage of CO₂ . This is a three year project to provide a more accurate and up to date assessment of the Vlaming Sub-basin prospectivity for the geological storage of CO₂ through the review of existing data and subsequent acquisition, processing, interpretation and integration of new data.

The Vlaming Sub-basin is a Mesozoic depocentre within the offshore southern Perth Basin which is located only 30 km from Perth, Western Australia. It covers an area of approximately 23 000 km² and contains sediments up to 14 km in thickness.

The main reservoir unit identified as suitable for storage of CO₂ is the Early Cretaceous Gage Sandstone (Figure 1) that overlies the breakup unconformity. The Gage Sandstone has an areal extent of approximately 1890 km² and a maximum thickness of 450 m.

Figure 1: Extents of the main reservoir
unit (Gage Sandstone) considered for
the geological storage of CO₂ in the
Vlaming Sub-Basin, showing Greenhouse
Gas (GHG) Release Areas offered in 2009
(not awarded) and Marine Protected Areas.

Western Australian industrial areas of Kwinana and Collie produce 0.25 TCF of CO₂ annually and so far no onshore CO₂ storage solutions have been demonstrated. Initial assessment of the offshore areas showed significant potential in the Vlaming Sub-basin (Causebrook et al., 2006) and resulted in offering GHG release areas (VLAM-01 and VLAM-02) to the industry in 2009 (Figure 1). No bids were received for these areas and currently no GHG permits are available in the Vlaming Sub-basin.

Subsequent assessment undertaken by the Carbon Storage Taskforce (CST) showed that the Vlaming Sub-basin can potentially store about 1 GT of CO₂ (Carbon Storage Taskforce, 2009). The CST recognised that the area required more data and a more detailed scientific investigation in order to better define storage potential and evaluate key risks associated with injection of the CO₂. This investigation is being undertaken by the Vlaming Sub-basin CO₂ Storage Section.

Status

This project is in its second year, continuing the work started within the Western Margin CO₂ Storage Section, which included the Vlaming Sub-basin and Browse Basin studies. In the first year (2011-2012), the project completed the initial phase of scoping the CO₂storage related issues in the area and determining data acquisition needs to assess these issues. The second phase involves acquiring and processing the data identified in phase one, including geological, geophysical and marine environmental data, as well as interpretation of existing datasets. Some data acquisition and initial interpretation occurred in the first year. The final phase of the project will focus on integration of the existing and newly acquired data into a full multidisciplinary assessment of the Vlaming Sub-basin for geological storage of CO₂.

Achievements to Date

In 2011-12, the study has focused on compilation and analysis of existing datasets, identification of the key science issues, data gaps and planning data acquisition to address them. During this period the section has completed:

• a detailed review of the previous work by CO₂CRC (2005-07) and Petroleum Prospectivity study (2008);
• the compilation and analysis of existing bathymetry, sub-bottom profiler data, SAR anomalies, petroleum wells and seabed samples;
• a preliminary tectono-stratigraphic framework;
• FIS analysis for 8 key wells providing screening and indications of potential migration and seepage above the South Perth Shale (regional seal);
• the analysis of available biostratigraphic data and the selection of wells/intervals of interest for new analyses to be done in 2012-13;
• the selection of wells/intervals of interest for specialised petrophysical analyses to be done in 2012-13;
• the mapping of major fault systems and the preliminary screening of hydrocarbon seepage signs in the seismic data;
• the initial sequence mapping from the seismic data;
• the definition of science objectives and the scoping of acquisition requirements for the new seismic data (survey in 2012-13);
• a marine survey (March-April 2012).

The Vlaming Sub-basin marine survey acquired 510 km² of high-resolution (2 m grid) multibeam bathymetry, 1700 km of sub-bottom profiler records, 57 km of side-scan sonar records and 104 grab samples (38 sediment samples, 52 biology samples and 14 geochemical samples, Figure 2).

Figure 2: Swath bathymetry and
samples collected during a marine
survey in the Vlaming Sub-basin.
Location of surveyed areas is
shown by red polygons.
© Geoscience Australia

The new data has showed that the Vlaming Shelf is a sediment-starved shelf with only isolated pockets of modern sediment generally less than 4 m thick. The shelf is dominated by prominent carbonate ridges and mounds that are built by rhodoliths (encrusting coralline algae). Some ridges spatially correlate with large faults mapped from the seismic data and therefore may indicate that their initial growth was related to hydrocarbon seepage. A more detailed interpretation of the survey data will take place in 2012-13.

References

Causebrook, R., Dance, T., Bale, K., 2006. Southern Perth Basin site investigation and geological model for storage of Carbon dioxide. CO2CRC Report Number; RP06-0162

Carbon Storage Taskforce 2009. National Carbon Mapping and Infrastructure Plan – Australia: Full Report, Department of Resources, Energy and Tourism, Canberra.