Transcript Slides

Scale Detection in Geothermal Systems
The use of nuclear monitoring techniques
E. Stamatakisa,b, T. Bjørnstadb, C. Chatzichristosb,
J. Mullerb and A. Stubosa
aNational Centre for Scientific Research Demokritos (NCSRD), Athens, Greece
bInstitute for Energy Technology (IFE), Kjeller, Norway
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Outline
 Nuclear experimental methods
 Gamma transmission experiments
 Method
 Typical results
 Gamma emission (tracer) experiments
 Method
 Typical radiotracer results
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Nuclear based methods
1. Gamma emission based on radioactive
tracers added to the flowing and
reacting system
2. Gamma transmission based on use of
external gamma sources
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Principles of gamma transmission
Absorption
sample
Gamma source
Io
Gamma detector
Ix
x
Transmission of a mono-energetic beam of collimated photons
through a simple absorption sample can be described by
Lambert-Beer’s equation
I x  Io  e
 is the linear mass absorption
coefficient with dimension L-1 (cm-1),
x the sample thickness
 x
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Mass absorption coefficient
A quantity more commonly found tabulated is the mass
absorption coefficient / with dimension cm2/g. In a composite
sample the attenuation is additive according to
I x m  Io  e
2 Alx m, Al 2Ca x m,Ca   x m,
(


)
 Al
Ca

XAl XCa
Xl
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XCa XAl
133Ba
The gamma source used in the present experiment is
133Ba due to suitable energies (see table below) and
half-life (10.5 y). Main gamma-ray energies and
intensities for 133Ba are:
E (keV)
Iabs(%)
80.998  0.008
34.0  0.3
276.397  0.012
7.16  0.07
302.851  0.015
18.3  0.1
356.005  0.017
62.0  0.8
383.851  0.020
8.9  0.1
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Experimental setup
7
Close-up look of -ray source and
detector arrangement
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Preliminary lab. experiments
RUN
SR
Temp.
C
Pres.
bar
Flowr.
ml/min
1
0.7
160
15
1
2
1.5
160
15
1
3-6
20
185
10
1
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Results from “Run 1”
4600
count-rate (cps)
4550
4500
4450
Gamma attenuation
measurements for calcite
precipitation at the inlet of the
tube at 160oC, 15 bars and
SR=0.7 (run 1)
background
4400
4350
0
6
12
18
24
time (hours)
10
30
36
42
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Results from “Run 2”
Gamma
attenuation
measurements
for calcite
precipitation at
the inlet of the
tube at 160oC,
15 bars and
SR=1.5 (run 2)
4600
count-rate (cps)
4550
4500
4450
background
tind
4400
4350
0
5
15
10
time (hours)
11
20
25
30
Results from “Runs 3-6”
Gamma attenuation
measurements for
calcite precipitation
in the presence and
absence of a scale
inhibitor 10cm from
inlet of the tube at
185oC, 10 bars and
SR=1.5 (runs 3-6)
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Calcite growth rate
0,275
0,250
Scaling rates (scale thickness
as a function of time) of calcite
precipitation at the inlet of the
tube for run 2 - preliminary
results
Scale thickness (cm)
0,225
0,200
0,175
0,150
0,125
0,100
0,075
0,050
0,025
0
0
5
10
15
Time (hour)
13
20
25
Calcite distribution across the tube
7000
1,00
0,90
background
6600
final
6400
6200
cps
0,80
scale thickness (cm)
6800
6000
0,70
5800
0,60
5400
5600
5200
0,50
5000
0
10
20
30
40
50
60
Position (cm)
0,40
Scale thickness
distribution across the
tube at the end of run 3
0,30
0,20
0,10
0,00
0
10
20
30
Position (cm)
14
40
50
60
Discussion on -transmission
The 133Ba-source (30 mCi or 100 MBq) gives a typical
counting rate of about 4500 cps (counts per second) in tube
filled with water (ID = 10 mm) with a detector collimator
opening of 4.5x4.5 mm.
The brine-filled tube reduces the normalized incident intensity
from 1.000 to 0.891when corrected for the Al-metal walls.
The increased mass thickness (g/cm2) due to scale obviously
leads to an increased attenuation and to a reduction in contrast
towards mass changes during the experiment.
Transmission experiments may be used to study calcite
scaling in open tubes with the dimensions used here.
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Principles of the -emission method
• CaCO3 scaling may be studied by radio-labeling of any
of the chemical components involved.
• However, for on-line, continuous and non-intrusive
detection, gamma-ray emitters are required.
• Neither O nor C have suitable gamma-ray emitting
isotopes.
• Ca has only one suitable radioactive isotope, namely
47Ca, with a half-life of 4.54 days.
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Protons
Chart of nuclides - How to produce 47Ca
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20
19
24
25
26
27
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Neutrons
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29
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Tracer- experimental setup
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On-line detector setup
• The main gamma energy of 47Ca is
1297 keV. However, by including also
its Compton background and lower
energies in the counting window, the
sensitivity in the experiment may be
increased.
• It is necessary to avoid contribution
from the 159 keV γ-quanta of the
daughter radionuclide 47Sc.
• The energy window for the detectors
will therefore be chosen from 350 keV
and upwards.
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Other measured parameters
• Samples are also collected periodically at the exit end of the
sandpack and the activity of 47Ca (1297 keV) in solution is
determined in off-line high-resolution gamma-spectrometric
measurements with a HpGe-detector coupled to a
multichannel analyzer.
• Solution temperature Ts, differential pressure Δp, pH,
absolute system pressure p and 47Ca2+ activity (counting rate
R) from the two on-line detectors are logged by computer
during the experiment.
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Typical tracer results (1)
80
70
60
cps
50
Add
NaHCO3
47
40
Ca background
scales
30
tind
20
10
Environmental background
0
0
20
40
60
80
Time (min)
21
100
120
140
Typical tracer results (2)
Typical results from a previous experiment with higher SR:
200
1,0
Ca(47)
tracer background
Δp
150
0,8
125
0,6
100
0,4
75
50
Δp (bar)
count-rate (cps)
175
0,2
25
0
0,0
0
20
40
60
80
100
120
140
Time (min)
47
47
Ca deposit growth at the inlet and Δp
buildup along the tube vs. time
Ca deposit growth in the presence and
absence of a scale inhibitor
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count-rate (cps)
Typical tracer results (3)
11
10
9
8
7
6
background Ca(47)
0-30 min
30-60 min
47
60-90 min
90-120 min
120-150 min
5
4
3
2
1
0
after 4 hours
0
1
2
3
4
5
6
7
8
9
10
11 12
13
Ca deposit distribution
across the tube at
different time-steps
14
11
10
9
8
7
6
5
4
3
2
1
0
12
total Ca(47)
10
initial Ca(47)
final Ca(47)
mgr CaCO3
count-rate (cps)
Position (cm)
precip. Ca(47)
8
6
4
2
0
5
10
15
20
25
30
35
40
45
50
55
0
60
0
Position (cm)
20
40
Position (cm)
Final distribution of the deposits across the tube
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60
Discussion on -emission
 The radiotracer 47Ca can be used to study CaCO3
precipitation in tube blocking tests providing the
following unique information:
 The induction time of CaCO3 scale deposition
 Visualization of the spatial distribution (concentration versus
position) of the CaCO3 scale deposition
All experiments with tracers showed that the tracer
monitoring gives a shorter induction time than monitoring
of the pressure drop
A novel technique for the determination of MIC, based
on the γ-emission method, can be developed.
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Final Conclusions
 Both methods are capable to visualize the distribution of the scale
deposits, a result that is not readily obtained by methods
commonly used in conventional dynamic scaling experiments.
 The techniques are sensitive to scaling, resulting generally in
shorter induction times compared to Δp-monitoring.
 The methodologies can be easily used for the laboratory
investigation of the scaling processes occurring in geological
systems, including oilfield, geothermal and hydrology applications
and for all kind of mineral scales.
 Their results are meant to be applicable at the field scale; the
quantification of the earlier occurrence of scale precipitation that
those techniques attain can be directly implemented in large scale
simulators.
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