Territory Stories

Summary of past drilling activity within the Great Artesian Basin, Great Artesian Basin Coordinating Committee

Details:

Title

Summary of past drilling activity within the Great Artesian Basin, Great Artesian Basin Coordinating Committee

Creator

Great Artesian Basin Coordinating Committee

Collection

E-Publications; E-Books; PublicationNT; D0851

Date

2017-11

Location

Great Artesian Basin

Description

The Great Artesian Basin Coordinating Committee (GABCC) requested bore hole data from the state and territory government databases to be collated to estimate the number of bore holes that have been drilled into the Great Artesian Basin (GAB). This is to inform discussions on the legacy of the 140 years of past drilling activity with respect to the long term management of the groundwater resources of the GAB.

Notes

Made available via the Publications (Legal Deposit) Act 2004 (NT).

Table of contents

Executive summary -- Introduction -- Scope -- Limitations of the data -- Summary of all available data -- Total number of reported bore holes drilled -- Date of construction -- Water bore data -- Drilling in areas of artesian conditions -- Water supply bore depths -- Estimated replacement value of water supply bores -- Number of bores with uncontrolled artesian flow -- Discussion -- Appendix A-E

Language

English

Subject

Great Artesian Basin; Drilling Activity

Publisher name

Great Artesian Basin Coordinating Committee

Place of publication

Australia

Series

D0851

Format

27 pages : colour illustrations, colour maps, tables ; 30 cm.

File type

application/pdf.

Use

Copyright

Copyright owner

Great Artesian Basin Coordinating Committee.

License

https://www.legislation.gov.au/Details/C2019C00042

Related links

http://www.gabcc.gov.au/

Parent handle

https://hdl.handle.net/10070/299513

Citation address

https://hdl.handle.net/10070/383677

Page content

6 4.1 Drilling in areas of artesian conditions The age profile for water supply bores shown in Figure 2 indicates that over 30 percent of these bores were drilled over 50 years ago. This also includes a significant number of bores that are sub artesian. That is, bores that are either shallower than the underlying artesian aquifers, or are drilled in areas where artesian conditions do not occur. Drilling and bore construction in artesian conditions must be able to accommodate the higher groundwater pressures and control flows to the surface. Consequently the drilling and construction standards for these conditions are more stringent to cope with this pressure. Early drilling activity, however, will not have employed aquifer isolation techniques as is the current practice and older bores that have not been reconditioned pose a higher risk of allowing flow between aquifers to occur via the borehole. This may be due to breached casing from corrosion, poor or little cementing resulting in ineffective sealing of the bore annulus. Non isolation of aquifers by the bore can compromise groundwater quality if there is a significant difference in groundwater water chemistry. These bores may also not have adequate headworks to control water flow. Issues associated with inter aquifer leakage due to drilling or bore construction is not limited to artesian conditions. It can also be an issue in sub artesian areas if multiple aquifers are intersected with different pressure heads. However areas with artesian pressure conditions, or had artesian conditions before widespread aquifer depressurisation, are known areas that have potential for aquifer leakage if not managed appropriately. Table 3 includes the number of water bores that obtained a flowing supply at the time of construction, and water bores drilled into areas to depths where artesian conditions exist, or previously existed under pre development pressure heads. This data is also shown graphically in Figure 3. It should be clarified this is not an indication of the water bores that are currently flowing or have flowed in the past, nor of the number of bores where the casing or sealing is compromised. The data indicates the minimum number of bores that required drilling and construction standards to ensure aquifer isolation and sealing. This data can inform an understanding of the potential risk from bores drilled prior to widespread adoption of aquifer isolation during drilling and construction. It has less relevance to more recent drilling activity. This is an underestimate of the bore holes in which there is potential for inter aquifer flow exchange as bores in areas of sub artesian pressure also have this potential. A more conservative approach would be to suggest all bores have the potential to allow inter aquifer exchange.