assessment of permeability of structures in mahanagdong using soil
TRANSCRIPT
Assessment of Permeability
of Structures in Mahanagdong
Using Soil Radon Gas Signatures
by JW Mismanos and AA Vasquez
GEOSCIENCES AND RESERVOIR ENGINEERING GROUP
ENERGY DEVELOPMENT CORPORATION
38/F One Corporate Center, Pasig City, Philippines
21 September 2013
• Mahanagdong
• Radon as a potential permeability indicator
INTRODUCTION
• Surveyed areas: MG-5 and MG-RD1
• The instruments and sampling procedure
METHODOLOGY
• Statistical analysis (EDA and population partitioning)
• Correlation with MG-RD1 and MG-5 wells
• Radon signatures in thermal areas
RESULTS
PRESENTATION OUTLINE
2
PHILIPPINE GEOTHERMAL PRODUCING FIELDS
3
MAHANAGDONG – A
� Installed Gross
Capacity
Main Plant – 120 MW
TCP – 12.7 MW
MAHANAGDONG (MG) IS ONE OF THE GEOTHERMAL
SYSTEMS IN THE GREATER TONGONAN GEOTHERMAL
FIELD
MAHANAGDONG – B
� Installed Gross
Capacity
Main Plant – 60 MW
TCP – 6.6 MW
RADON SIGNATURES CAN BE USED AS PERMEABILITY
INDICATORS IN A GEOTHERMAL RESERVOIR
• Radon is a intermediate daughter
of radium in the 238U decay chain.
• It occurs naturally in geothermal
systems (Wollenberg, 1975) and it
can be transported by HT fluids
(Semprini & Kruger, 1980).
• Fluid convection enables radon
migration to near-surface through
permeable conduits (Cox, 1980).
• High radon concentrations in the
soil can indicate rapid transport
through faults/fractures.http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/radser.html#c3
SPATIAL PATTERNS IN SOIL RADON CAN BE USED TO
DELINEATE STRUCTURES OF GOOD PERMEABILITY. 5
THE SOIL RADON GAS SURVEY METHODOLOGY AIMS
TO HELP WITH EDC’S HUNT FOR PERMEABILITY
• This study is part of the Collaborative Research Program on
Permeability.
• The survey was first tested in areas where knowledge of
permeability is available, with the following objectives:
– Compare soil radon gas signatures with permeability
reported from well geology and drilling data.
– Differentiate anomalous from background soil radon
concentrations by determining threshold values.
– Characterize radon concentrations in thermal areas.
6
TWO AREAS WERE SURVEYED:
EAST OF MG-RD1 & EAST OF MG-5
• Survey grid was patterned with a
150-meter point spacing.
• MG-5: 32 points in a 0.4 km2 area
• MG-RD1: 73 points within 1.5 km2
• Soil radon was also measured at
thermal manifestations:
– Kapakuhan
– Banat-i
– Hanipolong
– Mahanagdong
7
INSTRUMENTS FROM SARAD GMBH WERE USED IN
THE SURVEY
• The soil gas probe (SGP) houses
the radon accumulation and
detection chamber.
• Analogue radon sensor (ARS)
converts SGP inputs into digital
readings.
• The pictured instrument set-up
was implemented in sampling.
• Radon concentration is presented
as bequerels (Bq)/m3 i.e. decay
events per second in 1m3 of space.
• Duration of measurement: 1.5 hrs
(min. time for fast-mode: 60 min.)
8
EXPLORATORY DATA ANALYSIS STATISTICAL PROCEDURES
ARE APPLIED IN THE DATA REDUCTION OF SOIL RADON GAS
SURVEY DATA
9
STATISTICAL & GRAPHICAL ANALYSIS WAS USED TO
DETERMINE ANOMALOUS RADON CONCENTRATIONS
10
0
0.1
0.2
0.3
0.4
0.5
0.6
0 5000 10000 15000 20000 25000
Re
lati
ve
Fre
qu
en
cy
Soil Radon Gas (Bq/m3)
PAD MGRD1
0
0.1
0.2
0.3
0.4
0.5
0.6
1 2 3 4 5
Re
lati
ve
Fre
qu
en
cy
log [Soil Radon Gas]
PAD MGRD1 (Box-Cox)
R² = 0.9711
Sample Size: 6
R² = 0.9794
Sample Size: 65
R² = 1
Sample Size: 2
1.50
2.00
2.50
3.00
3.50
4.00
4.50
0 10 20 30 40 50 60 70 80 90 100
Lo
g [
So
il R
ad
on
Ga
s]
Relative Cumulative Frequency
Log Probability Plot of MGRD1
LOG Probability Plot Curve of Best Fit Population A (8.22%)
Population B (90.41%) Population C (1.37%)
R² = 0.9440
Sample Size: 4
R² = 0.9476
Sample Size: 28
2.00
2.50
3.00
3.50
4.00
4.50
0 10 20 30 40 50 60 70 80 90 100
Lo
g [
Rn
-22
2]
Relative Cumulative Frequency
Log Probability Plot of MG5
LOG Probability Curve of Best Fit Population A (12.5%) Population B (87.50%)
0
0.1
0.2
0.3
0.4
0.5
0.6
0 5000 10000 15000 20000 25000
Re
lati
ve
Fre
qu
en
cy
Soil Radon Gas (Bq/m3)
PAD MG5
0
0.1
0.2
0.3
0.4
0.5
0.6
1 2 3 4 5
Re
lati
ve
Fre
qu
en
cy
log [Soil Radon Gas]
PAD MG5 (Box-Cox)
MG-RD1
• Data distribution positively
skewed (leans to the left)
• Three populations discerned
• Anomaly < 284 Bq/m3
• Anomaly ≥ 8224 Bq/m3
MG-5
• Data distribution positively
skewed (leans to the left)
• Two populations discerned
• Anomaly ≥ 3098 Bq/m3
IN MG-RD1, HIGH SOIL RADON CORRELATES WITH
PERMEABLE STRUCTURES INTERSECTED BY WELLS
1. Intersection of Lower
Mahanagdong and Macape
Splay. Major permeable
zone of MG5RD.
2. Catmon Fault. Permeable
zones in MG5RD, MG6RD,
MG9RD.
3. Cabalonan Fault and CFL
intersection. All wells
reported poor permeability
in CFL.
4. Cabalonan-A and
Kinuhaan-C. Good
permeability in MG7RD
and MG8RD.
11
IN MG-5, MOST HIGH SOIL RADON CONCENTRATIONS
WERE OBSERVED AT FAULT INTERSECTIONS
1. Intersection of Mantugop-
C & Lumpag-A. Permeable
zone in MG36D.
2. North Mamban & Lumpag
Fault. Permeable in
MG36D, MG32D & MG27D.
Tight in MG18D & MG34D.
3. Mantugop Faults and
North Mamban
intersection.
4. Mantugop-B and Lumpag
Fault. Permeable zone in
MG18D.
5. Mantugop-A and Lumpag
Fault. Permeable zone in
MG32D.
12
ONLY TWO THERMAL AREAS SHOWED
HIGH RADON CONCENTRATIONS
766
5038
7794
1174 1429
36
733403 403
0
2000
4000
6000
8000
10000
Ra
do
n c
on
cen
tra
tio
n (
Bq
/m3)
13
MG-RD1 threshold value
MG-5 threshold value
THIS IS UNEXPECTED FOR THERMAL AREAS, WHICH ARE PERMEABLE
ZONES CONDUCTING GEOTHERMAL FLUIDS
SUMMARY
• A preliminary soil radon gas survey was executed in Mahanagdong to test
for the correspondence of radon signatures with reported permeability.
• Anomalous radon was determined to be 8,224 Bq/m3 and 3098 Bq/m3 for
MG-RD1 and MG-5, respectively.
• Good correlations were observed in MG-RD1 while MG-5 demonstrated
fair correlations.
• Thermal areas registered low soil radon contents.
14
THESE PRELIMINARY RESULTS WILL HELP SHAPE THE BASIS
FOR PERMEABILITY PROSPECTING IN MG-RL
IT IS HOPED THAT AN EVALUATION OF THIS
PROCEDURE WILL BE ACHIEVED AFTER
SURVEYS AT OTHER EDC SITES
• The preliminary results still warrant the study of factors that affect radon
concentration in soil or reservoir fluid degassing.
• Results of the soil radon survey in MG-RL must be integrated with results
from geological/structural mapping and geophysical imaging.
• Survey programs shall also be conducted in MAGBU this year and in
NIGBU next year.
• Conducting simultaneous investigations of other soil gases/substances,
e.g. CO2 & Hg, can reinforce the relationship of surface anomalies with
permeability at depth.
15
THIS MAY BE ESTABLISHED AS A GOOD PERMEABILITY-PROSPECTING
METHOD FOR EDC’S OPERATING AND EXPLORATION FIELDS.
STATISTICAL & GRAPHICAL ANALYSIS WAS USED TO
DETERMINE ANOMALOUS RADON CONCENTRATIONS
0
0.1
0.2
0.3
0.4
0.5
0.6
0 5000 10000 15000 20000 25000
Re
lati
ve
Fre
qu
en
cy
Soil Radon Gas (Bq/m3)
PAD MGRD1
0
0.1
0.2
0.3
0.4
0.5
0.6
1 2 3 4 5
Re
lati
ve
Fre
qu
en
cy
log [Soil Radon Gas]
PAD MGRD1 (Box-Cox)
R² = 0.9711
Sample Size: 6
R² = 0.9794
Sample Size: 65
R² = 1
Sample Size: 2
1.50
2.00
2.50
3.00
3.50
4.00
4.50
0 10 20 30 40 50 60 70 80 90 100
Lo
g [
So
il R
ad
on
Ga
s]
Relative Cumulative Frequency
Log Probability Plot of MGRD1
LOG Probability Plot Curve of Best Fit Population A (8.22%)
Population B (90.41%) Population C (1.37%)
17
A PILOT SOIL RADON SURVEY WAS CONDUCTED IN
MAHANAGDONG TO TEST OUT THE TECHNIQUE
PHASE 1
“Experimentation”
Verified Structures
Knowledge on Permeability Available
MG-5
MG-RD1
PHASE 2
“Actual Prospecting”
Most are Inferred Structures
Knowledge on Permeability Unknown
MG-RL
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R² = 0.9440
Sample Size: 4
R² = 0.9476
Sample Size: 28
2.00
2.50
3.00
3.50
4.00
4.50
0 10 20 30 40 50 60 70 80 90 100
Lo
g [
Rn
-22
2]
Relative Cumulative Frequency
Log Probability Plot of MG5
LOG Probability Curve of Best Fit Population A (12.5%) Population B (87.50%)
STATISTICAL & GRAPHICAL ANALYSIS WAS USED TO
DETERMINE ANOMALOUS RADON CONCENTRATIONS
0
0.1
0.2
0.3
0.4
0.5
0.6
0 5000 10000 15000 20000 25000
Re
lati
ve
Fre
qu
en
cy
Soil Radon Gas (Bq/m3)
PAD MG5
0
0.1
0.2
0.3
0.4
0.5
0.6
1 2 3 4 5
Re
lati
ve
Fre
qu
en
cy
log [Soil Radon Gas]
PAD MG5 (Box-Cox)
19