Vlaming Sub-basin CO2 Storage Project

Overview

As part of the National CO2 Infrastructure Plan (NCIP), Geoscience Australia is conducting a detailed study of the Vlaming Sub-basin for the long-term geological storage of CO2. The project will provide a more accurate and up to date assessment of the CO2 storage potential through review of existing data, new laboratory tests, interpretation, integration and modelling of different datasets.

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

The main reservoir unit, the Early Cretaceous Gage Sandstone (Figure 1), overlies the Valanginian breakup unconformity and was identified by previous studies as suitable for storage of large quantities of CO2 (Causebrook et al., 2006, Carbon Storage Taskforce, 2009).  The Gage Sandstone has an areal extent of approximately 1890km2 and a maximum thickness of 450m.

The figure shows the extent of the re-mapped Gage reservoir and demonstrates that almost all of it is covered by the effective seal. Bathymetry of the Rottnest shelf shows the location of the reservoir/seal pair in relation to the city of Perth and the Perth canyon offshore.

Figure 1: Revised extents
of the main reservoir unit
(Gage Sandstone) and the
overlying effective seal
(lower part of the South
Perth Shale, new interpretation).
Background image – bathymetry
of the Rottnest Shelf.

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 for CO2 storage in the Vlaming Sub-basin (Causebrook et al., 2006) and resulted in the release of two Greenhouse Gas (GHG) permits in 2009. 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 questions associated with injection of the CO2. The current study will provide this more detailed assessment.

Status

Current work focuses on completing interpretations undertaken in the past two years and integrating all results for an updated evaluation of the Vlaming Sub-basin CO2 storage potential by March 2014. The project has significantly advanced the understanding of facies distribution and palaeo-depositional environments for the main reservoir and seal units. Previous assessments of the Vlaming Sub-basin CO2 storage capacity relied solely on using the Gage Sandstone reservoir. Geoscience Australia’s new analysis evaluated the base seal and mapped out the underlying Charlotte Sandstone. Initial results reveal that the Charlotte Sandstone is an additional reservoir suitable for CO2 storage thus increasing the total storage potential of the Vlaming Sub-basin. In the second half of 2013, the project will construct a geological model of the sub-basin based on these new interpretations.

The study highlighted the critical importance of understanding the containment issues. A major focus of the present work has been detailed mapping of the regional seal. An initial scan of seismic data indicated potential fault reactivation. This prompted a detailed study of the seal integrity in collaboration with CSIRO to understand fault behavior under the present-day stress field. These results will be further analysed and integrated with the findings from Fluid Inclusion Stratigraphy (FIS) and Grain in Oil Inclusions (GOI) tests to provide a comprehensive and robust assessment of the regional seal.

Achievements to Date

In 2011-12 Geoscience Australia compiled and analysed existing datasets to identify the key science issues and to develop a scientific strategy to address them. During this period the following was completed:

  • A detailed review of the previous work by the CO2CRC (2005-07) and the petroleum prospectivity study by Geoscience Australia (2008)
  • compilation and analysis of existing bathymetry, sub-bottom profiler data, Synthetic Aperture Radar (SAR) anomalies, petroleum wells and seabed samples
  • development of a preliminary tectono-stratigraphic framework
  • Fluid Inclusion Stratigraphy analysis (FIS) for eight key petroleum wells to look for potential migration and seepage above the South Perth Shale seal
  • analysis of available biostratigraphic data and the selection of wells/intervals of interest for new biostratigraphic analyses to be completed in 2012-13
  • selection of wells/intervals of interest for specialised petrophysical analyses to be completed in 2012-13
  • mapping of major fault systems and the preliminary screening of hydrocarbon seepage signs in the seismic data
  • initial sequence mapping from the seismic data
  • definition of science objectives and scoping of acquisition requirements for new seismic data to be collected in 2012-13 [Acquisition was subsequently cancelled]
  • marine reconnaissance survey to investigate seafloor environments and shallow sub-surface geology in areas where seismic interpretation indicated seepage or fault reactivation (March-April 2012).

The Vlaming Sub-basin marine survey acquired 418km2 of high-resolution (2m grid) multibeam bathymetry (Figure 2), 2370km of sub-bottom profiler records, 57km of side-scan sonar records and 89 grabs (61 sediment samples, 52 biology samples and 14 geochemical samples).

The figure shows location of the surveyed areas in relation to bathymetry of the Rottnest shelf. It also shows examples of high-resolution bathymetry acquired during the survey. The top image shows carbonate ridges and the bottom, exposed bedrock in the inner part of the shelf.

Figure 2: Location of areas
surveyed during the Vlaming
marine survey (yellow polygons).
Examples of swath bathymetry
collected during the survey.

These new environmental data reveal that the Rottnest Shelf is a sediment-starved shelf with only isolated pockets of unconsolidated sediment generally less than 4m thick. The shelf is dominated by prominent ridges and exposed bedrock. 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.

In 2012-13, the study focused on developing an in depth understanding of the reservoir and seal through detailed seismic mapping and sequence-stratigraphic analysis of the well data. Compilation of paleogeographic maps for the key intervals underpins the new understanding of spatial and temporal variability in reservoir and seal facies. Several specialised studies have also been completed, as follows:

  • Revision of the Vlaming Sub-basin tectono-stratigraphic framework
  • palynological analysis of the Valanginian unconformity and the Gage Sequence in six wells (Macphail, 2012)
  • the newly developed sequence stratigraphic framework defining South Perth Supersequence based on the well log analysis and new biostratigraphic data
  • paleogeographic maps reflecting changes in sea level, location of main depositional systems and depositional environment for the Gage and South Perth sequences (Figure 3) 
  • petrophysical analysis of all wells intersecting the Gage Sequence
  • geomechanical assessment of the present-day stress field from image well data (Harvey, 2013)
  • a fluid inclusion study to assess the presence/absence of the hydrocarbon leakage through the South Perth Shale (Kempton, 2013);
    The paleogeographic map illustrates progressive build-up of the South Perth Shale deltaic sequence filling in the paleotopographic depression predominantly from the north and the south. Mapped environments include land, delta plain, shallow-marine part of the delta, detla front, pro-delta and deep water restricted marine. It also shows channels feeding the main delta complexes.

    Figure 3: Example of a
    paleogeographic map for
    the South Perth Shale
    showing its progressive
    development through a
    series of depositional phases.

  • engineering tests for a representative core sample from Gage Sandstone reservoir to evaluate changes of porosity and permeability under different confining pressures (Cinar, 2013);
  • a collaborative seal integrity modelling study to understand fault behaviour and stability under the current stress field and with increased pressure through injection of the supercritical CO2 (Langhi et al., 2013).

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.

Cinar Y., 2013, unpublished report. Core analysis results.

Harvey, N., 2013, unpublished report. Vlaming Sub-Basin Geomechanics Study.

Kempton, R., 2013, unpublished report. Assessing hydrocarbon leakage through the South Perth Shale, Vlaming Sub-basin: a fluid inclusion study.

Langhi L., Zhang, Y., Bernardel G. and Schaubs, P., 2013, unpublished report. Fault seal integrity in the Vlaming Sub-basin for CO2 storage.

Macphail M., 2012, unpublished report. Palynostratigraphic analyses of samples encompassing the Valanginian unconformity in Challenger-1, Mullaloo-1, Parmelia-1, Peel-1 & Warnbro-1; Wambro & Parmelia Groups, Vlaming Sub-Basin, Perth Basin.