Final_Tugas Hasil Dan Target

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Tugas Mata Kuliah Eksplorasi Geothermal

Tugas Ini Dipergunakan Untuk Memenuhi Syarat Mata Kuliah Eksplorasi Geothermal

Hasil dan Target Survey Lapangan Geothermal

Disusun oleh:

R. B. Fauzan Irshadibima 3712100010

Fuad Aulia Bahri 3713100007

Rizal Taufiqurrohman 3713100010

Nur Rochman Muhammad 3713100012

Adib Banuboro 3713100024

Fuaddur Zaki Kurniawan 3713100030

Nizar Dwi Riyantiyo 3713100031

Diptya Mas Nugraha 3713100042

Nur Muhammad Zain 3713100043

Dosen Pengampu:

Dr. Widya Utama, DEA

Jurusan Teknik Geofisika

Fakultas Teknik Sipil dan Perencanaan

Institut Teknologi Sepuluh Nopember2016


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Outline

Target

•Cap Rock

•Aquifers

•Recharge Area

Processing

Flowchart

• Parameter Table

• Expected Result

Result


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Target

Cap Rock

Figure.1. (a) Illustrasion of geothermal system. (b). The Thickness of Cap Rock based on the Map

Resistivity value is resulted from 2D magnetotellurics model and density value is resulted

from 3D gravity model. From these results, impermeable (caprock) area have a resistivity

value about ≤ 10 Ohm.m with curve pattern in which side is thicker and density values is

between 1,49 gr/cm3 and 2,4 gr/cm3 with distribution patterns from west to east and the depth

of top layer from caprock is about 500 to 1000 m, and the thickness of caprock in this area is

estimated about 500 meter to 1000 meter,type of material is secondary clay mineral and

controlled by Puncung Fault

(a)

(b)


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The target of exploration is depth of caprock. The depth can be determine using

geological logic in geological map. By using dip and strike, the continuous layer from

geothermal system for the example is cap rock. The Cap rock is formed by impermeable

rock such shale or silt (Eric Schuster,1973).

Figure.2. Geothermal System

The impermeable rock had value range at 2-20 103 ohm meter (Telford,1991). Take

the example case study that located in Arjuno-Welirang Volcanoes system. The cap rock is

below 3000 meters go down and the thickness in this case is about 1000 – 2500 meters.

Figure.3. Geothermal System of Arjuna Welirang Volcanoes

This result is from geophysical survey (ESDM, 2010). After known the prediction of caprock

depth from geological mapping and past survey we can estimate the spreading of current

electrode for resistivity measurement. From the spreading of electrode relation with the depth

penetration about 1/3 of total electrode distance to find the target(depth) if we use 2D

Resistivity methods (Wenner Configuration).


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Aquifers

Reservoir of geothermal system is rock formation in subsurface which can store and drain

the hydrothermal. Usually, reservoir have characteristic with high porosity and permeability.

Porosity can be used to save the hydrothermal and permeability to drain the hydorthermal, we can

use geoelectrical methods because if the response subsurface is low resistivity indicated layer with

high porous and high permeability. Then after we try to get information about depth of reservoir

rocks, its about 3 km from surface. For the example reservoir geothermal ussually in sand formation.

Figure 4. The Typical Electrical Resistivities of Earth Materials

Caprock is impermeable layer to trap the vapor from reservoir rock. Usually caprock havehigher density than reservoir rock and have low porosity. So cap rock have high ressitivity because

any fluid can’t flow in that layer (impermeable) and usually formation of this layer is shale stone.

Recharge Area

And the last component is recharge area. For recharge area we must looking for area with

very high permeability, because its will be easy for fluid throught into subsurface. Recharge area

serves to maintain the sustainability of the geothermal reservoir.

Reservoir

Cap rock


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Processing

Data Result

(Resistivity)

•Data acquisition using Geoelectrical Survey

•Data saved as Resistivity (ohm.meter)

Processing

usingRes2dinv

•This software designed to interpolate and interpret

field data of electrical geophysical prospecting (2D

Sounding) of electrical resistivity and induced

polarization

Exterminate

bad datumpoint

• This is the first step in the processing data using Res2dinv

• In this step, we exterminate bad datum point by looking the

overview of data and datum which has so much different

behaviour

• Straighter line, it means that the acquisition data is valid

Using robustconstrain,

smoothness,

finest mesh, ...

•This step is done in order to minimize the error

•Constrain, smoothness, finest mest, and the others will affect the forwardmodelling

•Lesser the error, it means that the forward modelling is near the original

Iterate until

error < 5 %

• In the forward modelling step, this step is done

•Iterazion meand that the process will be repeated untilthe forward modelling meets the lower error

•Usually, 5 iterazion is enough

Final Result

(Data)

•In this step, we got the forward modelling data

•From this data, we could :

•Determine the depth of the reservoar and caprock

•Distinguish geothermal elements

•Approximate the thick of cap rock

•After we make the interpretation, we will get the conclution

Figure.5. Flowchart Processing


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Table Parameters

Table.1. Electrical resistivity in geothermal survey

GeophysicalMethod

MeasuredParameter

PhysicalProperty

or Properties

PhysicalProperty

Model

Typical SiteModel

Potentialtarget

Electrical

resistivity

Potential

differences inresponse to

inducedcurrent

Electrical

resistivity

Resistivity –

depthmodel often

withinterpretedlayer boundaries

Geologic

hydrologic profile

Hot brines,

fluid-inducedalteration

zones, faults

Fig.6. A schematic plot showing the relationship between resistivity and temperature gradients. Such plots are useful in

roughly estimating the nature of the subsurface rocks in terms of their geothermal energy potential.

Fig.7. A schematic representation of resistivity-depth graphs for areas where temperature increases moderately with depth

(b), and for areas where temperature increases rapidly with depth (a) where a gas or dry steam layer may exist (from Meidav

and Tonani, 1976).


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Table.2. Resistivity range of some rock and material depend their condition

Formation Resistivity (Om)

Recent lava flow 5.000-50.000

Dense intrusives 10.000-15.000

Basalt 100-300

Palagonite 20-100

Basalt (T>50oC) 30-100

Palagonite (T>50oC) 10-15

Rock with brine 5-15

High temperature areas, fresh water 1-5


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Table.3. Geoelectrical work on geothermal survey

Part DepthParameter

Orde Range MethodMeasurement

ParameterSimple description

Physic Chemichal

Reservoir

(High Permeable)3 km

Temperature 3 100-400 oC Geothermometer Temperature

Chemical equilibrium

and surface temperature

relationship

Permeability 410-1 - 104 milidarcy

GeoelectricalPotential differences

in response to induced

current

Low resistivity zone,

indicate that the area hashigh permeability, and

hight fluid content

Porosity 0.3 -70 % EM,MT,Seismic

TEM-FEM,Themagnetic fields were

measured using induc

tion coils,time travel

and amplitude

Lower resistivity thansurounding rock,Use

correlation between core

sample porosity and AI

to determine high porosity zone

MagneticSuceptibility

Magnetic Remanent MagnetismRelatively low magneticsucept in alteration zone

Density 3 2260kg/m3 Gravity Gravity forceLow density at steam

filled zone

Caprock 3 km

Permeability -7< 10-7 cm/sec

impermeable

Geoelectrical

Potential differences

in response to inducedcurrent

hight resistivity zone

indicate that the area haslow permeability or low

porositydensity(clay) 3

1200-2200

kg/m3

Porosity

Recharge area

3 km or

depend

reservoir

depth

Permeability 3-4miliDarcy ,High

PermeableGeoelectrical

Potential differences

in response to induced

current

Low resistivity zone

indicate that the area has

high permeability, or

hight fluid content


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Expected Result

In geothermal exploration the choice of a particular method depends on the objective

and the cost of the survey. It should be noted that there is no single method or combination

of different methods that can be called optimum in all cases. The most suitable method may

vary for different geothermal fields. In this study topic we will use geothermal cases with

resistivity method.

After data processing is done with several step that have been arranged, the result or

output from this processing must have some criteria, so that the information given can tell us

indicate the parameter of targeted geothermal system. In general, the result that we wanted

from geothermal system can be represented by picture below,

Figure 8 geothermal System

As we can see, in the figure 8 geothermal system consists of heat source, reservoir,

cap rock and recharge area. The interdependence of these component make a good

geothermal system and can be functioned well , therefore we can use it effectively for energy

cause.

Not only the resistivity value that being a target of geothermal system, but also the

temperature has a part for looking which or what element of geothermal system could be (ex :

cap rock, reservoir, etc). This picture below show us temperature of geothermal system in

general,


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Figure 9 Temperature of Geothermal System

As we can see in figure 2 in geothermal system, temperature is increasing along with

depth. This means that in every change of temperatures we can find different geothermal

system element. And in every geothermal system in the world the temperatures is variated,

depends on its heat source characteristics.

For data processing, we use resistivity data. Following in this pictures below, show us :

Example 1

Figure 10. Resistivity Processing Result 1

As we can see at figure 10 above, the indication of potential geothermal reservoir is

having a high resistivity, and we can see that the reservoir is backed by some layer that

having a lower resistivity (10-50 ohm m), this can be indicate as the presence of cap rock in

this geothermal system. And the increasing of temperature along with the depth, is confirm

that there are geothermal system in this study area.


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Example 2

Figure 11. Resistivity Processing Result 2

In general, the geothermal reservoir rocks are characterized by low-resistivity

anomalies. The observed resistivity structure was found to correlate with hydrothermal

alteration minerals. In the present study, such an anomalous zone is also delineated and

mapped as can be seen in Figures 4. The high surface resistivity observed most likely

represents fresh basaltic rocks of postglacial volcanism where the surface resistivity is in the

range of 10-50.

The low resistivity anomaly in figure 4 indicates that the low-temperature alteration

minerals, smectite and zeolite come into play. It appears as a vertical low-resistivity structure

that extends from a few tens of metres from the surface to a greater depth at this location.This figure show a typical resistivity structure of a high-temperature geothermal system with

a low-resistivity cap underlain by a more resistive core that marks the zone of high-

temperature alteration minerals, the chlorite zone.


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Refference

Borouma by artificial neural networksnd.2005.Determination of compacted clay

permeability.Tehran:IUST

Duffild,Wendell.2003.geothermal energy-clean power from the earth heat.Virginia:USGSGhassmi,Abbas.2015.Geothermal Energy.US:CRC-Press

Goldstein,Barry.2011.Geothermal Energy.USA:Cambridge University Press

Harsh,Gupta.2007.Geothermal Energy: An Alternative Resource For The 21st

Century.Amsterdam:Elsevier.

http://classic.geology.ucdavis.edu/classes/geothermalresources_F2010/electrical/index.html

Huenges,Ernest.2010.Geothermal Energy System.Germany:WILLEY-VCH

MIT.2006.The Future of Geothermal Energy.US:MIT Press

Nicholson,K.1993.Geothermal Fluids.Verlag:Springer

Schoon.2011.Physical Properties of Rocks.UK:Elsevier

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