VGP Technical Report 5 - New vitrinite reflectance measurements from legacy core and cuttings

Category: Victorian Gas Program	Product Code: MP-R-159917
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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 vitrinite reflectance measurements have been acquired from selected legacy core and cuttings samples from proven and potential petroleum source rock formations in the Victorian onshore Otway Basin. The results of these analyses fill data gaps in the Geological Survey of Victoria (GSV) historical vitrinite reflectance dataset.

As part of the Victorian Gas Program (VGP) geoscience studies, GSV is evaluating petroleum systems components (reservoir, seal and source), to assess the petroleum prospectivity of the Victorian Otway Basin and estimate the potential for further conventional gas discoveries, onshore and offshore with Victoria’s jurisdiction.

The cores and cuttings were selected from GSV’s Drill Core Library in Werribee and included fine-grained carbonaceous and coal-bearing units and formations containing organic matter from the Otway, Sherbrook and Wangerrip groups.

Source rocks are an essential component of a working petroleum system. Without source rocks there is no petroleum generation. For petroleum to be generated, a source rock must be buried in the Earth’s crust and heated to a sufficient temperature. To assess source rock potential, the thermal maturity characteristics of source rocks must be understood. This is achieved by measuring the vitrinite reflectance of source rock samples.

Energy Resources Consulting Pty Ltd (ERC) in Brisbane was commissioned to measure vitrinite reflectance from 192 legacy core and cuttings samples taken from 35 wells and boreholes provided by GSV. In addition to the reflectance dataset, ERC also undertook organic matter abundance and HAWK pyrolysis to provide a complementary dataset for each sample.

Visual estimation of organic matter type and abundance was observed by a skilled technician who used a microscope to examine the mounted samples under both reflected and blue light fluorescence. Mean maximum reflectance was determined from a 2 μm² area at 546 nm using a total magnification of 500X. Photomicrographs of each sample were taken for reflected and blue light.

The new vitrinite reflectance data measurements complement legacy data sets, with the thermal maturity dataset now extended through regions that previously had no or little data. The vitrinite reflectance scale was used to correlate the results from ERC and GSV’s legacy data with the main zones and thresholds of petroleum generation. Initially, the results from this analysis indicate that the new dataset broadly agrees with the legacy data, with infilling most useful for the Killara Coal Measures and the Laira Formation, establishing a thermal maturation versus depth trend where previously there was little data.

The laboratory measurements presented in this report are being used to complete comprehensive source rock studies to assess the gas prospectivity of the Otway Basin by mapping the distribution, thickness and quality of the source rock units. The data will be incorporated into petroleum systems modelling to assess the prospectivity of the Otway Basin and estimate gas resource potential.

Bibliographic reference:
Revie, D.J., Crosdale, P.J. & Ranasinghe, P., 2019. New vitrinite reflectance measurements from legacy core and cuttings, Onshore Otway Basin, Victoria. Victorian Gas Program Technical Report 5. Department of Jobs, Precincts and Regions.

Download:
The downloadable version of this report is supplied in pdf format (2.3 MB), Attachment A1 (pdf 32.6MB), Attachment A2 (zip 232MB), Attachment A3 (zip 33MB) & Word accessible version (docx 2.7MB).