Characterisation of Geothermal Systems Through FTIR Mineral Analysis of Drill Cuttings for Exploration, Appraisal and Development

1. Characterisation of Geothermal Systems
Through FTIR Mineral Analysis
of
Drill Cuttings
for
Exploration, Appraisal and Development
P. Joseph Hamilton, Carmen Harris & Sigrid Hillier
Proceedings The 4th Indonesia International Geothermal Convention & Exhibition 2016, 10 - 12 August 2016.

2. Petrographic observations and X Ray Diffraction (XRD) and
Fourier Transform Infrared (FTIR) analyses have been used to
identify key minerals indicative of hydrothermal alteration and
hence geothermal potential in two samples of drill cuttings from
an Indonesian geothermal field. Analysis of bulk samples,
handpicked particle lithotypes and handpicked minerals together
indicate the presence of xonotlite, vaterite, chlorite and epidote.
These hydrothermal minerals together indicate formation from
hot aqueous fluids at temperatures greater than about 220-250°C.
Abstract

3. X ray diffraction (XRD)
thin section petrography
scanning electron microscope / energy dispersive X ray spectrometry
Fourier Transform Infrared (FTIR) spectrometry
no radiation
no chemicals,
smallest footprint,
simplest sample preparation
quickest sample preparation
most rapid analysis (30 seconds)
Well Site Mineral Analysis Methods

4. Outline
 What is Fourier Transform Infrared Spectrometry?
 How do we do it?
 Why do it?
Identify key hydrothermal alteration minerals indicating:
- thermal gradients
- cooler vs hotter regions
- permeable zones and barriers
- zones of upwelling and recharge,
- subsurface temperature distributions
Hydrothermal minerals change petrophysical properties of rocks
densities,
permeabilities,
electrical propertieshttp://www.crystalsrocksandgems.com/:www.mineralminers.com:ruff.info:www.mcdougallminerals.com:

5. What is Infrared Spectrometry?
 specific wavelengths absorbed identify atomic bonds and their host molecules
 mid range home of ‘fingerprint regions’ allows identification of many minerals
Wavelength mm
Wave number cm-1
INFRARED
4000 400
2.5 25
Near Mid Far
Measurement of wavelength + intensity of absorption of mid-infrared light by a sample

6. water
15002000250030003500
657075859095
AbsorbanceUnits
0.80
Wave number cm-1
15003500
What is Fourier Transform Infrared Spectroscopy?
Fourier Transform …… deconvolutes transmitted signal into component peaks
stretching
vibrations
deformation
vibrations
IR spectrum = absorbance units vs wave number

7. 500100015002000250030003500
0.00.40.8
Wavenumber cm-1
AbsorbanceUnitsInfrared Spectra
Si-O
Si-O
OHbonds
Al-OH
0AbsorbanceUnits0.8
4000 Wave number cm-1 500
Kaolinite Al2Si2O5 (OH)4

8. Infrared Spectra
5001000150020002500300035004000 Wavenumber cm-1
0.00.10.20.30.4
AbsorbanceUnits
4000 Wave number cm-1 500
Whole Rock Example: Dolomite + Quartz + Illite0AbsorbanceUnits0.5
I
I
D
Q
D

9. Well Site Operation = ThermMinTM
Simple - Wash, dry, grind, analyse. ~ 1 - 0.5g bulk cuttings, 50 mg handpicked rock types

10. Well Site Operation = ThermMinTM
Simple - Single mineral grains ~ few mg, automated id from spectra library for 100s minerals
Kaolinite sample with knife
Laumontite
CaAl2Si4O12.4H2O
Gmelinite
Na2CaAl2Si4O12.6H2O
single grain of scolecite
standard scolecite

11. The interaction of hot waters with rocks causes new minerals to be formed.
These hydrothermal minerals preserve evidence of physical – chemical conditions of formation
The factors affecting hydrothermal mineral formation:
 Rock Type
 Temperature
 Permeability
 Fluid Composition
Geothermal Energy Potential Assessed From Minerals

12. The factors affecting hydrothermal mineral formation:
Argillic Assemblages form low permeability seals over geothermal
reservoirs
- electrically conductive and characteristic low electrical resistivity
 Rock Type
 Temperature
 Permeability
 Fluid Composition

13. The factors affecting hydrothermal mineral formation:
At > 250°C Albite, Adularia, Epidote, Chlorite, Calcite, Muscovite,
water-poor zeolites (e.g. Xonotlite, Analcime) are common
At lower temperatures water rich zeolites (e.g. Wairakite, Mordenite)
and clay minerals (Illite, Smectite, Halloysite) are common
 Rock Type
 Temperature
 Permeability
 Fluid Composition

14.  Rock Type
 Temperature
 Permeability
 Fluid Composition
High abundance of a hydrothermal alteration mineral in cuttings sample
indicates fracture mineralisation and high permeability fluid pathway
Factors affecting hydrothermal mineral formation:

15.  Rock Type
 Temperature
 Permeability
 Fluid Composition
determines whether a
mineral will precipitate in
its field of stability.
epidote
prehnite
diaspore
grossular
Bruton, 1996)
Factors Affecting Hydrothermal Mineral Formation

16. XRD Analysis: Sample A: Handpicked lithotypes – 20-50 mg
0 20 2qo 40 60
4000
2000
0
counts XRD wt %
Mineral AP AV
serpentine 0 4
tobermorite 0 3
xonotlite <100 12
quartz trace 53
calcite trace 5
vaterite 0 23
AP
0 20 2qo 40 60
8000
4000
0
counts AV

17. Zeolite Minerals
- particularly indicative of temperatures of formation
- water rich varieties such as tobermorite prevalent at <150-200°C
- less water rich varieties such as xonotlite common at hotter levels in the
hydrothermal system
Vaterite
- CaCO3 polymorph stable at one atm. and T < 20 °C.
- metastable hydrothermal precipitate

18. FTIR Analysis of Cuttings Sample A - Indonesia
Handpicked lithotype - ~50 mg red crystalline particles
500100015002000250030003500
0.00.20.4
Wavenumber cm-1
AbsorbanceUnits
0AbsorbanceUnits0.5
4000 Wavenumber cm-1 500

19. FTIR Spectral Analysis:
Handpicked particles of quartz + alkali feldspar
500100015002000250030003500
0.000.100.20
500100015002000250030003500
0.000.100.200.30
500100015002000250030003500
0.00.20.4
Wavenumber cm-1
4000 Wavenumber cm-1 500
AbsorbanceUnits
sample
alkali feldspar
quartz
4000 Wave number cm-1 500
4000 Wave number cm-1 500

20. 500100015002000250030003500
0.050.150.25
500100015002000250030003500
0.00.20.4
Wavenumber cm-1
AbsorbanceUnits
4000 Wavenumber cm-1 500
4000 Wave number cm-1 500
AP
AV
FTIR Analysis of Cuttings Sample A - Indonesia
Handpicked lithotypes – pink and grey particles
XRD wt %
Mineral AP AV
serpentine 0 4
tobermorite 0 3
xonotlite <100 12
quartz trace 53
calcite trace 5
vaterite 0 23

21. Micro-sampled single minerals - 10-20 mg
FTIR Analysis of Cuttings Sample B - Indonesia
500100015002000250030003500
0.00.20.40.60.8
500100015002000250030003500
0.10.30.50.7
Wavenumber cm-1
AbsorbanceUnits
sample
chlorite standardAbsorbanceUnits
4000 Wavenumber cm-1 500
4000 Wave number cm-1 500
5 mm

22. 500100015002000250030003500
0.00.20.4
500100015002000250030003500
0.00.20.40.6
Wavenumber cm-1
FTIR Analysis of Cuttings Sample B - Indonesia
Micro-sampled epidote
sample
epidote standard
4000 Wave number cm-1 500
AbsorbanceUnits
4000 Wavenumber cm-1 500

23. ThermMinTM Technology at the Wellsite
FTIR
Elemental
geochemistry
XRD
well site well site
bulk semi-
quantitative
low cost higher cost higher cost
small footprint larger footprint larger footprint
direct mineralogy inferred direct
clay minerals inferred poor
few mg mineral analysis 0.5 g 3-5 g

24. pH Mineral Temperature Stability Range °C
100 200 300
Acidic
Alunite
Jarosite
Kaolinite
Pyrophyllite
Diaspore
Anatase
Illite
Muscovite
Neutral Epidote
Chlorite
Alkaline
Adularia
Vaterite
Tobermorite
Laumontite
Xonotlite
Composition –
Temp Controls
of
Hydrothermal
Mineral
Formation
for 2 cuttings
samples from
Indonesia
Metastable ….. boiling?
neutral to alkaline
220 – 240o
C
diagenetic after feldspar

25. Metastable ….. boiling?
diagenetic after feldspar

26. Drill Hole Isotherms
garnet biotite zone
prehnite epidote zone
muscovite zone
illitic zone
smectitic zone
0 --
0.5 --
1.0 --
1.5 --
2.0 --
DrilledDepthkm
Temperatureo
C
-100
-210
-250
Locate mineral zones in drill holes
Correlate to establish isotherms to reveal:
 thermal gradients,
 cooler vs hotter regions
 permeable zones and barriers
 zones of upwelling and recharge,

27. ThermMinTM Technology for Hydrothermal Minerals
a benchtop FTIR mineral analysis method (ThermMinTM) applicable to
Geothermal Exploration, Appraisal and Development
Simple sample preparation
Small sample size ~ 1 – 0.5 gm
Rapid analysis time (30 seconds)
Analyse handpicked lithotype particles
Analyse ~ few mg handpicked individual minerals
Analysis at well site / laboratory based in Jakarta /KL/Bangkok/ Perth
Key hydrothermal minerals identified from an extensive spectral library

28. Tourmaline
Prehnite
Xonotlite
Wairakite
Actinolite
EpidoteLaumontite
THE
END