Roadshow 1.2 Assessing the prospectivity for tight, shale and deep-coal gas resources in the GBA regions

Assessing the prospectivity for tight, shale and deep-coal gas resources in the Cooper Basin, Beetaloo Sub-basin and Isa Superbasin

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Good morning, everyone. Thanks for dialling in for the roadshow today. My name is Adam Bailey. I work for Geoscience Australia. I have been working the last couple of years on the Geological and Bioregional Assessments. Today I'll be presenting to you on our assessments of the prospectivity for tight, shale and deep-coal resources in the Cooper Basin, the Beetaloo Sub-basin and the Isa Superbasin.

Before I get started, I'd like to thank my co-authors listed below as well as the more extensive list of co-authors included on the GBA documentation, particularly the stage two geological and prospectivity reports, which you can find on the GBA website.

Okay, so the GBA Prospectivity assessments really started with stage one, where the basins were selected based on an initial stage of rapid regional prioritisation that was conducted by Geoscience Australia. 27 onshore basins with the potential to deliver shale and/or tight gas to the East Coast Gas Market were assessed. These were reduced to a shortlist of nine basins where exploration is currently underway. Shortlisted basins were ranked on criteria including prospectivity, interpretation confidence, access to markets and access to infrastructure.

As a result, the Cooper Basin, the Beetaloo Sub-basin , the McArthur Basin, and the Isa Super-basin were selected for assessment under stage two of the GBA program. You can see the matrix by which these basins were selected in the image to the right. Where we see increasing prospectivity on one side, these all had moderate to high prospectivity and increase in confidence in that prospectivity across the top. These all have moderate to high confidence in that prospectivity.

Moving to stage two, regional geological evaluations and conceptualizations were undertaken to establish a baseline understanding of the assessment regions. These data informed the assessment of relative shale and/or tight gas prospectivity. Relative prospectivity assessments provide an indication of where viable petroleum plays are most likely to be present within assessed regions and highlight the areal and stratigraphic constraints on play extent. These assessments help construct likely development scenarios and refine the scope of stage three impact assessments.

You can see on the right here, a figure showing the three GBA regions that were assessed as part of this program. From the top-left, these are the Beetaloo Sub-basin in the Northern Territory, the Isa Super-basin, in northwest Queensland and the Cooper Basin within South Australia and Queensland. I'll be presenting prospectivity results by basin in order of data availability and quality. Hence, we'll start with Cooper then go through the Beetaloo and finish up on the Isa.

Before we do that, I want to address the issue of GBA regions. This is a term you'll have heard already and which will come out through presentations throughout this meeting. The assessments occur within regions defined specifically for the GBA program known as GBA regions. GBA regions are identified not only on the known extent of each assessed geological basin, but include factors such as data availability and quality, the presence of a known petroleum system and likelihood of development being able to deliver gas to market.

You'll see on the right here, the SEEBASE model for the Isa Superbasin and related sediments within northwest Queensland or the Northern Territory. You'll see the area that is mapped by the blue and green colours shows area of significant sediment thickness. However, you'll see that the Isa GBA region is constrained to this area in the northwest outlined in the thick green line. This is purely because that is the area where the data is available to assess the prospectivity. The rest of the region, which is a large region, is potentially also prospective. However, when the GBA program was undertaken, the data did not exist to make this assessment.

Since then, Geoscience Australia has undertaken significant data acquisition programs through the Exploring for the Future program, which highlights potential prospectivity of this area. I encourage you to go to the EftF website to look into that. So prospectivity assessments were undertaken, following detailed evaluations of the structure and stratigraphic architecture in each GBA region. These provided the geological framework properties of stratigraphic sequences hosting potential probe petroleum resources. They also help identify the criteria we needed to assess the relative prospectivity for shale, deep-coal and tight gas plays.

As these were selected from the evaluated geological properties, for example, things like formation thickness and extent, source rock properties, reservoir characteristics and pressure and stress regimes. Separate criteria were developed for different play types within different regions. On the right here, you can see a figure representing schematically where the play types of interest are found, particularly the tight gas in the centre middle of the figure. Below that in the bottom middle of the figure, shale gas and deep-coal gas. Prospectivity assessments were undertaken using input maps developed from classify parameters representing each criteria. Input parameters were assigned a ranking between zero and one and where absent, these were all ranked zero.

Classified input parameter maps were multiplied together to highlight relative cost activity for each play type by formation. On the right, you can see a schematic representation of this where classified input parameter maps, one through to N are stacked on top of each other and multiplied to give the underlying combined or overall prospectivity for that formation play type. Further combined relative prospectivity maps for each play type are created by taking the maximum prospectivity value of the formation specific maps for that play type. To illustrate, think of a shale play, a basin with multiple shale plays in multiple formations. These are all stacked on top of each other and the highest value was taken for the overall map. In all of these maps, non mappable criteria were not integrated into the process activity mapping, but they were used to better understand the geological characteristics of the formations.

An example of working with this classified data can be seen here. This is the Murteree shale gas play within the Cooper Basin. We can see the classified input parameter maps here for the formation thickness, formation pressure, formation total organic carbon content, formation maturity and the hydrogen index of that formation across the formation. These have all been combined to create the combined relative prospectivity map for the Murteree shale gas play presented on your right, which illustrates in the purple to blue colours where low areas of overall prospectivity are located, mostly around that central area, which represents the Nappamerri trough of the Cooper Basin.

So moving into results, let's start with the Cooper GBA region. Three Cooper GBA region play types are assessed. These are the shale gas plays at the Patchawarra formation as well as the Roseneath and Murteree shales. We also assess the wet and dry deep coal gas plays, that's Toolachee, Epsilon, and Patchawarra formations and the basin-centred tight gas plays of the Gidgealpa Group.

Areas of higher prospectivity were identified within most epicentres, particularly the Nappamerri trough, Patchawarra trough, the Windorah trough, the Allunga trough and the Wooloo trough. This is consistent with recent exploration activity and relative prospectivity maps inform where the plays are most likely to be present within the basin. So going through these results, we can see here in the figures to the right, the central figure there represents the relative prospectivity across the basin for all of the assessed shale gas plays. We see two main areas particularly within the Nappamerri trough in the southwest. Moving up towards the northeast, we see the Windorah trough is also a likely spot for this.

Moving to tight gas, we see again the Nappamerri trough is a highly prospective area for this. This coincides with an area where exploration wells have been drilled for tight gas which you can see in the figure to the right. Finally, looking at the deep-coal gas, we see the play, potential plays are present across the basin. The highest areas particularly that from the Patchawarra trough, coincident with drilling that has occurred to date.

Moving to the Beetaloo GBA region, three Beetaloo GBA region play types were assessed, these being Velkerri formation, Amungee Member dry gas play; the Velkerri formation, Amungee Member liquids-rich gas play; and the Kyalla formation liquids-rich gas play. The extent of a fourth play type, the Hayfields Sandstone members liquid-rich gas play was derived from previous publications done by Coté et al. as there were insufficient public domain data to assess this play distribution. So, we merely represent the work that they have undertaken.

Results in the Beetaloo GBA region demonstrate that the Amungee member of the Velkerri Formation is potentially prospective for either liquids-rich or dry-gas over most of the Beetaloo Sub-basin extent. On the left in the upper two figures, we can see this. That leftmost figure represents the dry-gas extent. We can see it covers most of the eastern portion of the basin and a fair chunk of the north western part of the basin as well. Next to that, still on the upper line, we see the wet gas prospectivity. This fringes the dry gas showing that most of that area is prospective for one or the other.

The Kyalla formation liquids-rich gas play and the Hayfield Sandstone member liquids-rich gas and oil play are primarily restricted to the central part of the eastern sub-basin. These are mapped on the lower line where the leftmost figure shows us the Kyalla formation liquids rich gas play in the two blobs within the eastern sub basin. On the right of that, we have the mapped Hayfields Sandstone member liquids play extent from Coté et al.

Finally, the Isa GBA region, we looked at two play types, this being the Lawn Supersequence shale gas play and River Supersequence shale gas play. The results here demonstrate that the River Supersequence is potentially perspective for shale gas over most of the Isa GBA region. You can see that on the leftmost figure. The lower Supersequence, the right figure, is most likely perspective over the central and eastern parts of the region.

In summary, as part of the Australian Government's Geological and Bioregional Assessments Program, Geoscience Australia has undertaken detailed studies on the stratigraphic structural architecture of defined regions within three highly prospective onshore petroleum basins. A relative prospectivity mapping process has been undertaken in these regions, identifying and mapping the likely extent of shale, tight and deep-coal gas plays. These maps provide key inputs into stage three of the GBA program indicating areal and stratigraphic constraints that support further work on likely development scenarios, impact assessments and causal pathways for each GBA region. These will all be talked about throughout the roadshow today.

Thank you for your time today listening to my talk. If you have further questions that can't be answered by going to the GBA link below, which I would encourage you to do so because that is where all the products are found. Please feel free to contact either myself at Geoscience Australia, or Mitchell Bouma at the Department of Agriculture, Water and the Environment. Thank you very much.

Additional information

About the presenter

Dr Adam Bailey

Geoscience Australia

Adam is a Petroleum Geoscientist with the Onshore Energy Systems team at Geoscience Australia and is currently working on the flagship Exploring for the Future Program. He is the geology discipline lead for the Geological and Bioregional Assessment Program. 


Last updated:
15 November 2021