Groundwater 2010:

the challenge of sustainable management

National Groundwater Conference31 Oct – 4 Nov 2010, Canberra Australia

Cara Danis & Dr Craig O’NeillGEMOC, Department of Earth and Planetary Science,

Macquarie University, Sydney, Australia

A static method for collecting

temperatures in deep groundwater bores

for geothermal exploration and other

applications

Objectives• Brief history of the geothermal exploration

in Australia

• Role of groundwater bores

• The static measurement methods

• Case study - other applications

History of the Geothermal in Australia

• Exploration in the early 90’s by the

Australian Geological Survey Organisation

• The first geothermal dataset combined

over 3000 bottom-hole temperatures from

exploration drilling

• Auscope and Geoscience Australia are re-

entering existing exploration bores and

deep groundwater bores to log

temperature

Austherm07 Temperature at 5km Map

Geothermal Exploration

Geothermal exploration has two main

requirements:

• High accuracy bottom-hole temperature

measurements and

• Good data coverage

But there is also a need for equilibrated

bottom-hole measurements for thermal

modelling of potential geothermal

resources

The Role of Groundwater Bores

• Existing bores provided opportunity to expand the geothermal data set

• Groundwater column provides thermal coupling

• Gives a good indication of the temperature of the host formation and surrounding geotherm

• Are generally equilibrated if greater than 3 months old

The Static Method

• Geophysical temperature logs lower a thermistor at a slow speed providing continuous temperature readings

• Static methods uses thermistors at discrete intervals for set periods of time for individual temperature readings

• The greater the time spent recording at an interval the more accurate the temperature measurement

The Static Method

Two methods using HOBO™ loggers

Equipment Specs:

- Range: -20 C to 50 C

- Accuracy: 0.37 C (at 20 C)

- Resolution: 0.1 C (at 20 C)

- Recording interval: 1sec

Measurements collected in 29 groundwater bores

Measurement

Locations

50m

100m

150m

200m

Method A

1hr total

50m

100m

150m

200m

20mins per interval

Method B

RESULTS

Method A

15

17

19

21

23

25

27

29

31

33

35

9/03/2010

15:21

9/03/2010

15:36

9/03/2010

15:50

9/03/2010

16:04

9/03/2010

16:19

9/03/2010

16:33

9/03/2010

16:48

9/03/2010

17:02

9/03/2010

17:16

9/03/2010

17:31

Te

mp

era

ture

(C

)

250m 225m 200m 150m 100m 50m

Enter Water Column

Method B

16

17

18

19

20

28/07/2010 12:28 28/07/2010 12:57 28/07/2010 13:26 28/07/2010 13:55 28/07/2010 14:24 28/07/2010 14:52

Te

mp

era

ture

(C

)

100m

150m

170m

200m

Enter Water Column

RESULTS

Repeatability

Method A

Depth (m) 23/12/2009 11/02/2010 Difference

100 18.045 18.045 0.000

150 18.557 18.557 0.000

Depth (m) 23/12/2009 11/02/2010 Difference

25 18.806 18.711 0.095

75 19.187 18.996 0.194

125 19.758 19.853 0.095

150 20.234 20.126 0.108

175 20.460 20.460 0.000

GW75093/4

GW75402/2

Depth (m) 10/06/2009 12/03/2010 Difference

80 19.662 19.662 0.000

130 20.710 20.710 0.000

230 26.292 26.304 0.012

PZ26A

All measurements are within the accuracy (0.37 C) of the logging unit

Method A vs B

Depth

(m)

A

9/03/2010

B

14/07/2010

Difference

100 20.901 20.805 0.096

150 21.569 21.664 0.095

200 22.333 22.333 0.000

225 22.561 22.633 0.072

250 22.944 22.968 0.024

Depth

(m)

A

12/03/2010

B

19/09/2010

Difference

55 19.282 19.151 0.131

80 19.662 19.555 0.107

130 20.71 20.603 0.107

180 23.677 23.665 0.012

205 24.871 24.871 0.000

230 26.304 26.280 0.024

GW75098/3 PZ26A

All measurements are within the accuracy (0.37 C) of the logging unit

Case Study:

Temperature and Borehole Failure

Background

• During temperature measurement

collection in March 2009 noticed the BHT of

borehole A was 5 C cooler than nearby

and deeper boreholes

• Groundwater level measurements showed

a 28m rise in water level in A

• Suspicions of casing/grout failure resulting

in aquifer mixing lead to an18 month study

of the BHT

Nest Piezometric Groundwater Levels

0

10

20

30

40

50

60

70

80

90

24-Mar-06 10-Oct-06 28-Apr-07 14-Nov-07 1-Jun-08 18-Dec-08 6-Jul-09 22-Jan-10 10-Aug-10 26-Feb-11

Dep

th (

metr

es b

elo

w c

asin

g)

A

B

C

Bottom-hole Temperature at 290 mbc for Borehole A

20

21

22

23

24

25

26

27

28

29

30

24-Mar-06 10-Oct-06 28-Apr-07 14-Nov-07 1-Jun-08 18-Dec-08 6-Jul-09 22-Jan-10 10-Aug-10 26-Feb-11

Tem

pera

ture

(C

)

290

Case Study Conclusions• Borehole casing or grout appears to have failed, probably above

the standing water level, thus causing one or more of the upper

aquifers to mix within the water column

• This mixing caused a drop in bottom-hole temperature

• The bottom hole temperatures slowly increases in response to

groundwater level increase and stabilisation

• Over 15 months the bottom-hole temperature has increased 4.5 C

• Over the last 3 months the bottom-hole temperature appears to be

stabilising with the host rock formation

• These results show that disturbance to the groundwater column

significantly affects bottom-hole temperatures and thermal

equilibrium must be re-attained

CONCULSIONS

• Both methods are simple and effective in collecting down-hole temperature measurements

• Method A, although faster, requires more logging units

• Method B creates the least amount of disturbance to the water column and requires only one logging unit

• Both methods are repeatable within the accuracy of the logging unit

• Method A and B produce comparable results for the same borehole

• Any disturbance to the water column, such as cleaning or aquifer leakage, will affect the resultant temperature

• Time needed to re-equilibrate with host rock temperatures depends on the amount and length of disturbance

• Static measurements in deep groundwater bores, provided they are equilibrated, add valuable data for geothermal exploration

Acknowledgements

NSW Department of Primary Industries

NSW Department of Environment, Climate

Change and Water

Ulan Coal Mines Ltd

Coffey Geotechnics

Hydroilex