They apply large scale, long term, multidisciplinary science and .... groundwater management along the reach of the river from the Carnarvon township to about.
Earth Science and Resource Engineering www.csiro.au
Gascoyne River Airborne Electromagnetic (AEM) Survey III: Drilling Target Selection Report Aaron C Davis, Timothy J Munday, and Richard J George Report Number: EP-13-12-353 January 2015 Prepared for: Department of Agriculture and Food, Western Australia (DAFWA)
Water for a Healthy Country Flagship Report series ISSN: 1835-095X Australia is founding its future on science and innovation. Its national science agency, CSIRO, is a powerhouse of ideas, technologies and skills. CSIRO initiated the National Research Flagships to address Australia’s major research challenges and opportunities. They apply large scale, long term, multidisciplinary science and aim for widespread adoption of solutions. The Flagship Collaboration Fund supports the best and brightest researchers to address these complex challenges through partnerships between CSIRO, universities, research agencies and industry. The Water for a Healthy Country Flagship aims to provide Australia with solutions for water resource management, creating economic gains of $3 billion per annum by 2030, while protecting or restoring our major water ecosystems. The work contained in this report is a collaboration between CSIRO and the Department of Agriculture and Food, Western Australia. For more information about Water for a Healthy Country Flagship or the National Research Flagship Initiative visit www.csiro.au/org/HealthyCountry.html. Citation: Davis, AC, Munday, TJ, and George, RJ, 2015. Gascoyne River airborne electromagnetic survey III: Drilling Target Selection Report. CSIRO: Water for a Healthy Country Flagship Technical Report (EP-13-12-353).
Copyright and disclaimer © 2015 CSIRO To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO.
Important disclaimer CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it.
Contents Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Gascoyne River aquifer and groundwater characterization project . 1.2.1 Project Area . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.2 Hydrogeology . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Project Objectives and Scope . . . . . . . . . . . . . . . . . . . . 1.3.1 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Report scope and objectives . . . . . . . . . . . . . . . . . . . .
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2 Analysis of borehole data . . . . . . . . . . . . . . . . . . . . . 2.1 Simplification of lithology . . . . . . . . . . . . . . . . . . . 2.2 Lithology compared to AEM . . . . . . . . . . . . . . . . . . 2.3 Conductivity of water compared to AEM . . . . . . . . . . .
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3 Selection of borehole targets . . . . . . . . . . . . . . . . . . . 3.1 AEM conductivity contours . . . . . . . . . . . . . . . . . . 3.2 Bore targets . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Assessment of targets . . . . . . . . . . . . . . . . . . . . .
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25 25 31 31
4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
39
Appendix A AEM inversion table . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Appendix B AEM conductivity contours . . . . . . . . . . . . . . . . . . . . . . . .
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Appendix C Planned exploration bores . . . . . . . . . . . . . . . . . . . . . . . .
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Acknowledgement This work is undertaken by CSIRO as part of a research collaboration with Department of Agriculture and Food, Western Australia (DAFWA), supported by the Western Australia Government’s Royalties for Regions Program and the CSIRO-led flagship Water for a Healthy Country. The Department of Water, Western Australia, contributed resources to aquire the AEM over the Basin A groundwater area (town and plantations) and assisted in the evaluation of available Government data. We would also like to thank Kevin Cahill (CSIRO) for his assistance in the field; and Dave Skidmore and Richard Nixon (Global Groundwater) for input into our understanding of the hydrogeology of the Gascoyne River system and for providing access to their reports, borehole lithology descriptions and geophysical logs.
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Executive summary The Department of Agriculture and Food, Western Australia (DAFWA) has identified priority areas across the State of Western Australia where land and water investigations are required to assess the capacity for further development of agriculture and related businesses. The Gascoyne River floodplain aquifer, in the arid mid-northwest of Western Australia, is one such area. As part of a collaboration between DAFWA and CSIRO the Gascoyne River AEM Aquifer and Groundwater Characterization Project was established with the aim of determining whether airborne electromagnetic (AEM) data can be employed to better map attributes of the unconfined alluvial aquifer beneath and adjacent to the ephemeral Gascoyne River, including spatial variations in groundwater salinity. The primary purpose of the project is to better inform groundwater management along the reach of the river from the Carnarvon township to about 50 km inland by helping constrain a 3-dimensional model of the aquifer system, thereby helping to secure additional groundwater resources for irrigated agriculture and providing a basis for mitigating against damage from salinity. The Gascoyne River AEM Project involves the acquisition, processing, and inversion of highresolution airborne electromagnetic data in a block area consisting of approximately 1500 km of survey flight line data oriented north to south, crossing the Gascoyne River east of Carnarvon and stretching to Rocky Pool. Results from the AEM survey are interpreted from a hydrogeological and geophysical point of view. The over-arching intent is to inform a planned drilling program along a 50 km reach of the Gascoyne River and assist in the refinement of a groundwater model of this region of the catchment. We divide the primary objectives of this project into two main categories: AEM and drilling. Each category has objectives that will assist in the hydrogeological interpretation of this reach of the Gascoyne River and inform the drilling campaign. We plan to achieve the following: 1. AEM: (a) Detect lateral and vertical variations in groundwater salinity in the Quaternary alluvial aquifer along and adjacent to the Gascoyne River at the reach scale; (b) Detect the boundary between the Quaternary alluvial aquifer which overlies a Late Cretaceous and Cainozoic basement; (c) Discriminate, where possible, facies variations within the Quaternary alluvial aquifer; (d) Identify the extent of the saltwater interface. 2. Drilling Campaign: (a) Inform a planned drilling program for a 50 km reach of the river; (b) Use new and existing borehole data to help verify and constrain the AEM interpretation. (c) Inform groundwater modelling that uses information from the AEM interpretation and the drilling campaign to aid future decisions. In this, the third of a series of technical reports, we interpret the AEM inversion results in a hydrogeological and hydrogeophysical context. We take the information from the AEM inversion and grids and combine it with borehole information based on lithology, geophysical logs, and groundwater salinity measurements. Our aim is to achieve item (a) of objective 2 from the above list, with the result of placing targets for a planned drilling program along the Gascoyne Gascoyne AEM Drilling Target Selection Report | 3
River. Once a drilling campaign is complete, we will add to the characterisation of groundwater resources along the Gascoyne river to achieve an improved groundwater model of this section of the catchment area. Having shown that the the AEM inversion results and grids are valid descriptions of the geoelectrical properties of the subsurface in the Gascoyne area, we explore the lithological records from the previous drilling campaigns and separate them into high- and low-permeable material classes. We then show the difficulty of determining material class from AEM conductivity-data alone, and offer a different approach based on water salinity sampled from the screened intervals of monitoring and production bores. We show, as would be expected, that increase in bulk conductivity of the host material is associated with an increase in water salinity. This therefore gives us impetus to seek out areas of low conductivity in the AEM conductivity grids. In this report, we devise a method of seeking out continuous areas of low conductivity that are adjacent to the Gascoyne River and inside the groundwater allocation zone outlined by Department of Water (cyan outline in Figure 1.2). This consists of creating contour curves of the AEM conductivity over the range of inversion layers that correspond to the most frequently occurring range of screened zones from the production and monitoring bores. Focussing on intermediate depth of between 20 m and 55 m below surface, we use contoured grids to locate the areas of deep and continuous zones of low conductivity in the assumption that they will be associated with areas of low water salinity and, hopefully, areas of greater production rates for production bores. A comparison of our selected targets to the existing production wells shows that the conductivity-depth profiles of our target locations match the conductivity-depth sections of the production wells.
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List of Figures 1.1 1.2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 B.1 B.2 B.3 B.4 B.5 B.6 B.7 B.8 B.9
Ternary image of merged regional radiometric data sets across the Gascoyne region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plan view of the Gascoyne River AEM survey area . . . . . . . . . . . . . . . . Location of boreholes that have lithology records in the Gascoyne AEM survey area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Histograms of the intercepted depths and elevations from the drilling records . AEM conductivity for each basic lithology unit . . . . . . . . . . . . . . . . . . AEM conductivity-elevation histogram for limestone units . . . . . . . . . . . AEM conductivity-elevation histogram for silt units . . . . . . . . . . . . . . . AEM conductivity-elevation histogram for clay units . . . . . . . . . . . . . . . AEM conductivity-elevation histogram for silt units . . . . . . . . . . . . . . . AEM conductivity-elevation histogram for sand units . . . . . . . . . . . . . . AEM conductivity-elevation histogram for gravel units . . . . . . . . . . . . . . AEM conductivity-elevation histogram for impermeable units . . . . . . . . . . AEM conductivity-elevation histogram for permeable units . . . . . . . . . . . AEM conductivity-depth histogram for impermeable units . . . . . . . . . . . AEM conductivity-depth histogram for permeable units . . . . . . . . . . . . . Histograms of screened interval occurrences . . . . . . . . . . . . . . . . . . . AEM conductivity compared to electrical conductivity of sampled bore water . Conductivity-depth grid AEM inversion layer 08 . . . . . . . . . . . . . . . . . Contoured conductivity-depth grid of AEM inversion layer 08 . . . . . . . . . . Contoured conductivity-depth grid of AEM inversion layers 08 to 16, superimposed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conductivity-contour depth grids . . . . . . . . . . . . . . . . . . . . . . . . . Total conductance from 22.1 m to 52.9 m . . . . . . . . . . . . . . . . . . . . Groundwater exploration targets . . . . . . . . . . . . . . . . . . . . . . . . . Production bores located in the Gascoyne AEM survey area . . . . . . . . . . . Conductivity-depth profiles for the production bores in the Gascoyne AEM survey area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conductivity-depth profiles for the bores target locations in the Gascoyne AEM survey area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contoured conductivity-depth grid of AEM inversion layer 08 . . . . . . . . . . Contoured conductivity-depth grid of AEM inversion layer 09 . . . . . . . . . . Contoured conductivity-depth grid of AEM inversion layer 10 . . . . . . . . . . Contoured conductivity-depth grid of AEM inversion layer 11 . . . . . . . . . . Contoured conductivity-depth grid of AEM inversion layer 12 . . . . . . . . . . Contoured conductivity-depth grid of AEM inversion layer 13 . . . . . . . . . . Contoured conductivity-depth grid of AEM inversion layer 14 . . . . . . . . . . Contoured conductivity-depth grid of AEM inversion layer 15 . . . . . . . . . . Contoured conductivity-depth grid of AEM inversion layer 16 . . . . . . . . . .
11 12 14 16 17 19 19 20 20 21 21 22 22 23 23 24 24 27 27 28 29 30 32 34 35 36 44 44 45 45 46 46 47 47 48
List of Tables 2.1 3.1
Tabulation of lithology units . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of grid masking to detect channels . . . . . . . . . . . . . . . . . . .
15 26
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A.1 Inital model parameters for the final inversion of Gascoyne AEM data for conductivitydepth models. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 C.1 Location and priority for the borehole target locations . . . . . . . . . . . . . 50
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1 1.1
Introduction Background
The Department of Agriculture and Food, Western Australia (DAFWA) has identified priority areas across the State of Western Australia where land and water investigations are required to assess the capacity for further development of agriculture and related businesses. The Gascoyne River floodplain aquifer, in the arid mid-northwest of Western Australia, is one such area. As part of a collaboration between DAFWA and CSIRO the Gascoyne River AEM Aquifer and Groundwater Characterization Project was established with the aim of determining whether airborne electromagnetic (AEM) data can be employed to better map attributes of the unconfined alluvial aquifer beneath and adjacent to the ephemeral Gascoyne River, including spatial variations in groundwater salinity. The primary purpose of the project is to better inform groundwater management along the reach of the river from the township of Carnarvon to about 50 km inland by helping constrain a 3-dimensional model of the aquifer system and thereby help secure additional groundwater resources for irrigated agriculture and providing a basis for mitigating against damage from salinity. The research collaboration, funded in part by the Western Australia Government’s Royalties for Regions Program and CSIRO’s Water for a Healthy Country Flagship, involves the acquisition, processing and interpretation of high resolution AEM data to assist the targeting of additional drilling and supplementation of the existing groundwater resources available for agricultural development. The research aim is to select an appropriate AEM system for acquiring high-resolution geophysical data in an area with high cultural noise, to process and interpret acquired AEM data to define subtle changes in ground conductivity that relate to facies variations (and higher yielding zones) in the alluvial aquifer, and to map groundwater salinity in three dimensions. To our knowledge, there are no published studies of this type for the region. Our studies will address this challenge, and link the results with an active drilling and groundwater modeling program to quantify available supplies in aquifers that are currently being used for irrigated agriculture, and to identify future sources of water that can support its extension in the region.
1.2 1.2.1
Gascoyne River aquifer and groundwater characterization project P A
The Gascoyne River extends about 700 km inland from the coast of the Indian Ocean and the township of Carnarvon in the mid-northwest of Western Australia. This Gascoyne River AEM study is focussed on the western-most reach of the river, extending inland from Carnarvon for some 50 km, and is represented by the yellow rectangle in Figure1.1. The Lower Gascoyne River flows ephemerally along a well-confined singular, low-sinuosity channel, up to 1200 m wide, incised 3 m to 5 m into a laterally extensive Quaternary sequence of aggrading alluvial sediments (up to 60 m thick in places) that rest unconformably on an early Cainozoic and Mesozoic sedimentary sequence of the Carnarvon Basin (Dodson, 2008). The geometry and spatial extent of these alluvial sediments accords with them being part of an alluvial megafan. Megafans are part of a broader classification of alluvial fans and have been defined as large fans greater than 30 km in length (apex to toe) and an extremely low slope gradient
