Application of Integrated Geophysical Surveying for Modelling Hot Spring Aquifer at Sungai Klah,...

Application of Integrated Geophysical Surveying for Modelling Hot Spring Aquifer

at Sungai Klah, Perak, Malaysia

Amin KHALIL, Nawawi MOHD, John KAYODE*, Saheed ISHOLA

Universiti Sains Malaysia, 11800 USM, Pulau-Pinang, Malaysia.

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PresenterJohn Stephen Kayode

Universiti Sains Malaysia, School of Physics, 11800 USM,

Pulau-Penang, Malaysia. On the behalf of other Authors.

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We lead  AOGS-2015 AGENDA

We lead  AOGS-2015 INTRODUCTION

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A model of an idealised geothermal system modified after Geothermal 2015

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Geological and Structural Setting of Sungai KlahThe area is bounded by Granitic intrusion (pink colour) to the northeast. Surface geology is mainly schist and Phyllite from the paleozoic age. As seen in the map, the vicinity of the Sungai Klah possesses number of fault traces (source: Sime Darby, Perak)

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Instrumentation

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Seismic Reflection ProfileRaw profile

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Seismic Reflection ProfileRaw profile Location

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Processing flow-chart

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After Pullan et al, 1991.

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Software Used for the Seismic data analysis

In the present work we used two open source and free software. These software are:

1- Obspy: Python suite for seismological applications. We used OBSPY to convert the SEG2 format of the field recordings into SEG-Y files.

2- Seismic Unix (SU) to process the data. SU is used under UBUNTU in the present study.

AOGS-2015 GEOPHYSICAL METHODS

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Processed Profile

TW

T

(sec)

Distance (m)

Possible water saturation region at about 100m depth

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MASW

MASW technique uses the dispersion characteristics of surface waves to determine subsurface shear wave velocity. The technique requires identification of the dispersion curve of surface. Dispersion curve represents the change of velocity with frequencies. The non linear inversion of this curve yield S-wave velocity.

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Location Lines for MASW

Two 2-D MASW profiles was carried out. The length of both was 23m. The geophone interval was 1m. The source offset was set to 20m. The recording length was 0.8 sec.

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Model for MASW Line 1

In this line we observe too small S-velocity down to depth of 5m which may represent high water saturation. Then the velocity increase rapidly to almost 400 m/s. Two interesting features are observed. The first one is possible cavity or void with (Sv=200-230 m/s). This void is associated with possible fault.

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Model for MASW Line 2

This line is located near the surface occurrence of hot spring. It shows what may be interpreted as shear zone. This shear zone may represent the structure controlling hot water path to the surface.

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TEM Survey

Five profiles were conducted in the area. The first two lines are in the same straight line, hence we analysed as one extended line. In this presentation two lines are presented. Line 1 and line 5. Line 5 is located south of the hot spring area. Loop size used was 96 x 96m with single loop layout.

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Line 1 (extended line)

Corrected decay curves

Inversion Model using http://geomodl.info/tdem

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Gravity Data Interpretations Bouguer anomaly map

The gravity data was obtained usingScrintex CG-2 and CG-5 gravity meter. The stations selected for measurement of the Gravity data at arelative interval of 25m due to theconditions of land use in this area.The principal objective of applying gravity method is to define the subsurface structures of the area.The structures beneath the hotsprings possesses higher gravityvalues.

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3D-Euler Deconvolution model3-D Euler Deconvolution technique was applied For quantitative modeling of the subsurface structures.It has the ability to delineatecontacts and sources for subsurface anomalies therebymaking it a powerful technique for estimating the depth and the geometry of the buried geologic sources. Twomain structural trends wasobserved present in the area.The first trend seems to be

dominant roughly in the E-W direction, whilst the other trend is nearly N-S direction.

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At the eastern border of the hot spring area, we have relatively deep N-S trend that achieved depth of about 100m.These trends were interpreted to represent the pathway for the underground hot water to go up to the surface.

3D-Euler Deconvolution model

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Geomagnetic Data Interpretations

In constracts to the gravity anomaly, we observed lower susceptibility underneath the hot spring area.This could be due to the subsurface HEATING.For quantitative modeling, Reduction to the Pole (RTP) filter and Euler Deconvolution were applied.

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• Magnetic residual maps reveal much more detailed subsurface geologic features in particular, the geometry and configuration of individual basement blocks.

• The method brings out the subtle magnetic anomalies that result from the changes in rock types across the basement block boundaries.

• The presence of faults is a common interpretation of a magnetic increase or decrease.

• The study area present total magnetic intensity (TMI) values that varied from high to very low along the north-south directions.

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RTP and 3-D Euler Deconvolution model

The lowest value of about -600nT was recorded, while the Highest value of about450nT was alsoRecorded in the area. The trends also followNW-SE and NE-SWDirections as delineated by theGravity method.

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Geophysical techniques applied showed that the shallow depths were dominated by low resistivity. Low resistivity values were also observed near the surface in areas where hot spring is unlikely to be present.

The presence of schist and weathered Granite with resistivity as low as 20 ohm.m and < 1 ohm.m respectively lead us to believe that the aquifer is far deep down.

Seismic reflection showed the possible presence of water saturated layer near the hot spring at a depth of 100m. This may be interpreted as water accumulation but not the aquifer because the lateral extent is about 170m.

We leadAOGS-2015 Conclusion

Gravity and geomagnetism showed the existence of faults that are conjugate in the trends of NW-SE and NE-SW. The presence of these faults near hot spring may represent the subsurface structures controlling hot water flow to the surface.

Gravity analysis using Euler Deconvolution showed the presence of Granitic intrusion under the hot spring area.

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What is the depth of the aquifer? Rough estimate using geothermal gradient in hydrocarbon provinces nearby, assuming also the heat flow density is nearly the same can be obtained. Surface temperature of water is almost 99 I C, where geochemical analysis showed the aquifer temperature to be almost 145 IC. Hence, the loss of temperature is almost 46 I C. Geothermal gradient is nearly 4-6 I per 100m. Consequently, the depth to the aquifer could be larger than 800m. From other similar cases the aquifer is at depths ranged from 1-3 Km.

AOGS-2015 The Question?

We leadAOGS-2015 ACKNOWLEDGMENTS

for your kind attention.