VGP Technical Report 3 - Mineralogical and textural characterisation of sedimentary rock samples

Category: Victorian Gas Program	Product Code: MP-R-159137
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Product description:

About the Victorian Gas Program:
The Victorian Gas Program (VGP) is a comprehensive science-led program, incorporating geoscientific and
environmental research to assess the risks, benefits and impacts of potential onshore conventional gas
exploration and production.

The program is also investigating the potential for further discoveries of onshore conventional and offshore gas in the Otway and Gippsland geological basins and assessing the feasibility of additional onshore underground gas storage in depleted reservoirs around the Port Campbell area.

The VGP includes an extensive, proactive and phased community and stakeholder engagement program,
through which the results of the scientific studies are being communicated.

Executive summary:
New mineral analysis has been undertaken as part of the Victorian Gas Program (VGP) from selected legacy core and cuttings samples and three surface samples taken from 21 sedimentary geological formations in the Victorian onshore Otway Basin.

As part of the VGP geoscience program, the Geological Survey of Victoria (GSV) is studying petroleum systems components (reservoir, seal and source) to assess the petroleum prospectivity of the Victorian Otway Basin and estimate the potential for further onshore and offshore discoveries within Victoria’s jurisdiction.

Mineral analysis of geological units will help GSV to understand the contribution of different mineral suites and textures to variations identified in reservoir and sealing lithologies. The mineral analysis also contributes to better characterisation of the Otway Basin sedimentary sequence as a stand-alone study.

Advanced Reservoir Quality Services (ARQS) at SGS Pty Ltd was commissioned by the GSV to undertake QEMSCAN (Quantitative Evaluation of Materials by Scanning Electron Microscopy) and XRD (X-Ray Diffraction) analysis to characterise the mineralogy and petrography of legacy core and cuttings samples. Samples were taken from most sedimentary units in the Victorian Otway Basin including the Casterton Formation, Pretty Hill Formation, Laira Formation, Eumeralla Formation, Heathfield Sandstone, Waarre Formation, Flaxman Formation, Belfast Mudstone, Nullawarre Greensand, Skull Creek Mudstone, Paaratte Formation, Timboon Sandstone, Pebble Point Formation, Pember Mudstone, Dilwyn Formation, Mepunga Formation, Narrawaturk Marl, Clifton Formation, Gellibrand Marl, Port Campbell Limestone and Bridgewater Formation. One hundred and eighty rock core and cuttings samples were collected from 58 legacy petroleum wells and boreholes held at the Werribee core library by the Geological Survey of Victoria (GSV) and three samples from surface locations. Many of the samples were duplicates of samples previously analysed as part of the VGP reservoir and seal studies.

QEMSCAN and XRD analysis were conducted on the samples following standard ARQS preparation and procedures. The results for the 180 samples are presented in this report with data sheets included in Attachment A1.

To facilitate comparison of the results, the samples were grouped into three broad lithologies: sandstones, siltstones/mudstones and carbonates. These lithologies were further categorised into 30 lithotypes. Sixteen sandstone lithotypes are described in this report: Arkose, subarkose and subarkose – coarse; argillaceous sandstone; calcareous sandstone; chloritic sandstone; chloritic sandstone (porous); coarse sandstone; dolomitic and ferroan dolomitic sandstone; Fe hydroxide sandstone; glauconitic sandstone; kaolinitic sandstone; K feldspar subarkose; K feldspar subarkose – coarse; immature sandstone; sandstone; sideritic sandstone and silty sandstone. Seven siltstone/mudstone lithotypes are described: arkosic siltstone; glauconitic mudstone; illitic mudstone; kaolinitic mudstone; micaceous mudstone; smectitic mudstone and subarkosic siltstone. There are fewer carbonates in the sample set with three lithotypes described: argillaceous limestone, limestone and calcareous mudstone; dolostone and sandy limestone.

As part of the VGP, these new mineral analyses will be integrated with existing data and other new VGP data sets. Mineral composition and textural rock information will be used to understand more about the genesis and diagenesis of the Otway Basin stratigraphic sequence. Particular mineral groupings may inform a better understanding of provenance, whilst the identification of mineralogy, textures and cements will assist with sedimentary facies determination.

Bibliographic reference:
Power, M. & Goldie Divko, L.M., 2019. Mineralogical and textural characterisation of sedimentary rock samples, Onshore Otway Basin, Victoria VGP Technical Report 3. Department of Jobs, Precincts and Regions.

Download:
The downloadable version of this report is supplied in PDF format (112 MB), Attachment A1 (xlxs 310 kb) and Word accessible version (docx 396MB).