GABATLAS - Birkhead-Walloon Aquitard - Thickness and Extent

## **Abstract** 

This dataset and its metadata statement were supplied to the Bioregional Assessment Programme by a third party and are presented here as originally supplied.

The Birkhead-Walloon Aquitard - Thickness and Extent data sets, are part of a set that represents the hydrostratigraphic units of the Great Artesian Basin, which include five major aquifers, four intervening aquitards, and the Cenozoic cover to the GAB.



There are five layers in the Birkhead-Walloon Aquitard map data.



A: Formation Extent

B: Outcrop extent

C: Isopach Raster

D: Isopach Contours

E: Data Point Locations



The datasets have been derived from the lithostratigraphic intercepts in drillhole data from petroleum exploration wells, water bores, and stratigraphic wells. Seismic correlation and assessment of hydrogeological character based on electrofacies have not been used. The working datasets for this study has been derived primarily from the following databases:



1.	PEPS-SA (Petroleum Exploration and Production System - South Australia) (Department of Primary Industries and Regions SA, 2011)

2.	WaterConnect Groundwater database (Govt. of SA, 2011)

3.	QPED (Queensland Petroleum exploration database) (Geological Survey of Queensland, 2010).

4.	GABLOG (Great Artesian Basin Well Log Dataset) (Habermehl, 2001)

5.	Additional supplementary information was derived from published reports listed in the following section.



This is a regional interpretation for mapping at approximately 1:1 000 000 to produce a broad scale overview, and examination of small areas by collecting extra data is most likely to produce results that differ from this regional interpretation.



This dataset and associated metadata can be obtained from www.ga.gov.au, using catalogue number 81681.

	

Associated report reference:

Ransley, T., Radke, B., Feitz, A., Kellett, J., Owens, R., Bell, J. and Stewart, G., 2014.  Hydrogeological Atlas the Great Artesian Basin. Geoscience Australia. Canberra. \[available from www.ga.gov.au using catalogue number 79790\]



REFERENCES:

References - main data sources



\*	Department of Primary Industries and Regions SA (2011). Petroleum Exploration and Production System - South Australia (PEPS-SA).  Version 2011-06-15. Retrieved from http://www.pir.sa.gov.au/petroleum/access_to_data/peps-sa_database

\*	Geological Survey of Queensland (2010). Queensland Petroleum Exploration Data (QPED) database. Retrieved 25 September 2011, from http://mines.industry.qld.gov.au/geoscience/geoscience-wireline-log-data.htm.

\*	Geoscience Australia, 2013. Mesozoic Geology of the Carpentaria and Laura Basins (dataset). Scale 1:6000000. Geoscience Australia, Canberra. \[available from www.ga.gov.au using catalogue number 75840\]

\*	Govt. of South Australia (2011). WaterConnect Groundwater database \[available at https://www.waterconnect.sa.gov.au\].

\*	Habermehl, M. A. and J. E. Lau (1997). Hydrogeology of the Great Artesian Basin Australia (Map at scale 1:2,500,000). Canberra, Australian Geological Survey Organisation.

\*	O'Brien, P. E. (2011). The eastern edge of the Great Artesian Basin: relationships between the Surat and Clarence-Moreton basins. Internal report. Canberra, Geoscience Australia.

\*	Wells, A.T. , O'Brien, P.E. 1994 Lithostratigraphic framework of the Clarence-Moreton Basin IN Wells, A.T. and O'Brien, P.E. (eds.) "Geology and Petroleum Potential of the Clarence-Moreton Basin, New South Wales and Queensland" Australian Geological Survey Organisation. Bulletin 241 p4-47

## **Dataset History** 

SOURCE DATA: 

Data was obtained from a variety of sources, as listed below:

\*	WaterConnect Groundwater database (Govt. of SA, 2011)

\*	Great Artesian Basin Well Log Dataset (GABLOG) (Habermehl, M. A., 2001).

\*	Petroleum Exploration and Production System - South Australia (PEPS-SA) (Department of Primary Industries and Regions SA, 2011).

\*	Queensland Petroleum Exploration Database (QPED) (Geological Survey of Queensland, 2010).

\*	Well completion and drill log reports (see references in abstract)

\*	Other reports (see references in abstract)

\*	Seismic surveys and associated reports (see seismic references section in abstract)



METHOD:

Formation Extent

The extent was based on 1:500k mapping of Wells & O'Brien (1994) and drillhole data (see References for main data sources).



Extent lines were adjusted to envelop all borehole intercepts of the Hydrostratigraphic unit. This produced some varied and irregular shapes, some patchy regions, and required some interpretation to establish the most likely extent boundary. 



Outcrop Extent

Outcrop extents were taken from Hydrogeology of the Great Artesian Basin Australia (Habermehl & Lau, 1997) for the Eromanga and Surat sub-basins. For the Carpentaria Basin, Mesozoic Geology of the Carpentaria and Laura Basins (Geoscience Australia, 2013) was used. 



Isopach Raster

Drillhole intercepts in Clarence-Moreton from O'Brien (2011) were used to calculate isopach values by using the depth to top and bottom values of formations within the drillhole database attributes, and adding them together to form the isopach values for each data point across the whole aquifer/aquitard. These values were extrapolated using the ESRI ANUDEM Topo-To-Raster surface modeller tool to generate the isopach raster grid (thickness). Zero thickness constraints were applied at the known extent of the aquifer/aquitard, except in cases where the formation extends beyond the GAB boundary (for example the Precipice formation on the eastern side of the GAB, where the formation is quite thick and is exposed as a cliff). In these cases, constraints were not applied and the software was allowed to model a thickness right up to the GAB boundary.  Resulting grids were modified using the ESRI Grid Calculator to set the minimum thickness to 0, and clipped to the aquifer/aquitard extent.



Isopach Contours

Isopach contours were calculated from the Birkhead Walloon Aquitard thickness grid (generated from drillhole intercepts in Clarence-Moreton from O'Brien (2011)) using the ESRI Contour Tool. These were calculated at 50m intervals. In most cases the zero contour lines generated by the tool were replaced by the extent of the aquifer due to the erratic nature of the generated lines. In cases where the aquifer/aquitard is thick at the extent, the zero isoline is outside the extent and is not mapped in that area. Isopachs were clipped to the aquifer/aquitard extent.



Data Point Locations

Data Point Locations have been derived from the bore hole data collected for this project. Only the location has been included.



SOFTWARE:

All modifications/edits and geoprocessing were performed using ESRI ArcGIS 10 software.



QAQC:

Data sets were searched for errors such as negative thickness, missing data, incorrectly calculated thickness, aquifers/aquitards with missing formations, and false XY data.

The data was given a second Q&A after the thickness grids had been calculated. This involve plotting the points and the thickness grid and looking carefully for bad values. Sometimes a false outlier value would cause a 'bullseye' effect on the grid. To check the veracity, nearby data would be compared, and if necessary the original data would be searched check the value. Some petroleum fields would have wildcat picks at certain bore holes and these were compared with nearby boreholes and adjusted or deleted.

Additionally, if whole subregions had suspect values the data was check to ensure the relevant data had all been included. Finally, data sets were also checked to ensure the bore whole data recorded the full thickness of the Aquifer. In many cases water bores only go down until a suitable water source is found and often will not penetrate the whole aquifer. This data was considered on a case by case basis, in areas where plenty of suitable data was available they were removed, and in areas of sparse borehole data they were included to establish the occurrence of the formation albeit as a minimum thickness value.



Data has undergone a QAQC verification process in order to capture and repair attribute and geometric errors.

## **Dataset Citation** 

Geoscience Australia (2015) GABATLAS - Birkhead-Walloon Aquitard - Thickness and Extent. Bioregional Assessment Source Dataset. Viewed 07 December 2018, http://data.bioregionalassessments.gov.au/dataset/a5912292-10cd-42e2-aefe-49aae2eead4b.

Tags: Cooper subregion, Galilee subregion, geoscientificInformation
Organization: Bioregional Assessment Program