GEOTHERMAL MAPPING

USING TEMPERATURE

MEASUREMENTS

By

Godwin Mwawongo

Reservoir Engineer

Introduction

• Geothermal energy is

heat from the earth

• The earth is made of:

• Core 7000 km

• mantle 2900 km

• Oceanic crust 5-100

km

• Continental crust 30-

100 km

Geothermal system formation

• Located close active tectonicplates

• Tectonic activity results in faulting

• Hot rocks are brought close tosurface

• Water seeps through deep faults

• It’s heated by the hot rocks

• Pressure builds up

• Faults provide leakage path

• Heat loss features are formed inthe leakage areas

• Hot springs, fumaroles, hotgrounds are formed

Heat loss mechanism

• Heat loss features continuously transfer heat and

mass from the geothermal system to the

atmosphere

• Heat can be transferred by: conduction

– conduction

– convection

– Radiation

• Heat-loss in geothermal systems is mainly through

– conduction

– convection.

• Estimate amount of heat being lost naturally

• Analyze the distribution of the heat loss features

• Ranking the prospect for development

• Results obtained can be used as an indicator of the

heat source size

• Give an indication of the magnitude of recharge

• Indicates extent of leakage through the capping.

• Assists in locating hidden fracture zones.

Objectives of heat loss survey

Planning the mapping process• Spacing of shallow gradient holes

depend on surface geothermalactivity in the prospect

• 100 m – 1 km in an area ofhigh thermal activity

• 1 - 4 km in an area of lowactivity.

• Area, time and resources available

– This determines how fast thework is to be accomplished

• Geological formation of the area

– Some important features e.g.caldera

• Social constraints

– Some areas are prohibited orcontrolled due to their socialimportance (religious, touristattraction, cultural)

Conductive heat flow

• Heat transfer through solids

• Caused by temperature

gradient between two

surfaces

• Flow of heat energy is from

high to low temperature

• Hot grounds are conductive

heat loss features

Conductive heat flow

(con’t)

Where

• Q Conductive heat flow (watts),

• A Surface area of hot ground (m2),

• k Thermal conductivity of rock

(w/m C),

• T Temperature difference ( C)

• y Depth change (m).

dy

dTAkQ

Convective heat loss

• Natural convection trigged by,

density variation due to heating

• Results in pressure differential

• Fluid moves from high pressure to

low pressure

• Fluid transport the heat from one

point to another.

• In geothermal systems, hot springs,

fumaroles, steaming grounds

transport heat & mass to the surface.

• Convective heat loss is a product of

mass flow and enthalpy change

Measurements in boreholes

• Down hole temperature measurement

– Bore holes serve as temperature gradient holes

– Results can be used to estimate temperatures at depth

• Down hole pressure measurements

– Can assist in modeling the hydrological picture of the area

– Give an indication of possible recharge and outflow zones.

Down hole temp/press

measurements• Down hole temperature and

pressure tools are used

• Mechanical Kuster tool

• Deflection is measured

• Temperature and pressure computed from calibration curves

• Temperature gradients computed from resulting profiles

• Piezometric level obtained from pressure profiles

• Hydraulic gradient obtained from piezometric levels

0 20 40 60 80

Temperature (°C)

0

40

80

120

160

Depth

(m

)

4 8 12 16 24 28 32 36 44 48 52 56 64 68 72 760 20 40 60 80

KBHL-1

KBHL-2

KBHL-3

KBHL-4

KBHL-5

KBHL-6

KBHL-8

KBHL-9

KBHL-10

KBHL-11

KBHL-12

Down hole temperature

profiles

0 1 2 3 4 5

Pressure (ba)

0

40

80

120

160

Depth

(m

)

KBHL-1

KBHL-2

KBHL-3

KBHL-5

KBHL-8

KBHL-9

KBHL-10

KBHL-11

KBHL-12

Down hole pressure profiles

•14 geothermal prospects in

Kenya

•Estimated power potential is

over 3000 MWe

•Geothermal Resource

Assessment (GRA) was

formed to fast track

geothermal power

development

•From 2004 to 2007 studies

have been conducted from

Menengai to Paka

•Heat flow measurements

included.

Geothermal Prospects in Kenya

Menengai-Olbanita Prospect

• Associated with the 90 km2 MenengaiCaldera

• Heat flow survey covered an area of about 900 km2.

• Conductive heat loss features mainly hot grounds

• No hot springs were encountered.

• Convective heat loss is by fumaroles/ steaming grounds in the caldera

Menengai

Olbanita

180170160

9990

9980

9970

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2 100

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L. NAKURU

NAKURU TOWN LANET

R . N j or o

KIA

MU

NYI

ES

TAT

E

NGATA FARM

M E NE N GA I S TAT IO N

KABARAK ESTATE

CALDERAENGOSHURA FARM

KABATINICrater stream

BAHATI

SOLAI

BANITASISAL ESTATE

OLBANITA SWAMP & POND

Olba

nita s

tream

kabaragi

KISANANA

MAJANI MINGI ESTATE

ATHINAI SISAL ESTATE

EL BONWALA

OL' R

ON

GA

I HIL

LS

MENEGAI HILL FARM

KAMPIYA MOTO

MOGOTIO

0 10KMLEGEND

200

0Contours in meters above sea level

Roads

Railway line

Rivers

Lake, Pond

Shoppingcenter

Pyroclastic issuecrates

Lava eruption center

Major (r ift scarp) fault

Rift floorfault

Inferred fault

00

II

Borehole

FumarolesProposed exploration well site

MW-1

MW-3MW-2

MW-3

MENENGAI

40

50

60

70

80

Menenegai-Olbanita• Orientation of heat loss

features is NNW-SSE and NE-SW

• Total conductive heat loss is 1060 MWt

• Total convective heat loss is 2476 MWt

• Caldera:250 MWt Conductive

2440 MWt Convective

• This indicates large heat source for the prospect

Arus-Bogoria Prospect , cont’d

Arus &

Lake Bogoria

• Not associated with a central volcano

• Heat loss features are hot springs,

geysers, hot grounds & steam jets

• Most of the convective heat loss

occurs at Lake Bogoria

• Total heat loss from the two prospects

is in excess of 1666 MWt

Arus steam jet

Geyser at

L Bogoria

Arus

Bogoria

Arus and Lake Bogoria

• Total heat loss from the

two prospects is 1666

MWt

• Conductive 1229 MWt

– Lake Bogoria 762 MWt

– Arus 467 MWt

• Convective 437 MWt

– Lake Bogoria 437 MWt

– Arus 0.03 MWt

Lake Baringo Prospect

• Lake Baringo covers a large

part of this prospect thus,

reducing the effective area

substantially

• Thick alluvial deposits lowers

natural heat loss as it acts as

an insulator

• Has no central volcano

• The area covered by the lake

could also be absorbing the

natural heat flow underneath.

Lake Baringo

Lake Baringo prospect

• Anomalous bore holes have

been drilled in this prospect

• A 90 m bore hole

discharging boiling water.

• Conductive heat loss is by

hot grounds

• Convective heat loss by

fumaroles

Lake Baringo Prospect

Eastings

Tanglubei

Paoyi

Riongo

Loruk

Chesirimion

Chemiril

Kadogoi

Cepkalacha

Komolion

1

2

3

45

6 78

9

10

11

12

13

14

15

16

1718

19

2021

L Baringo

OlKokweisland

°C

Legend

Craters

Contours

Roads

Paka Craters

Lake Tulam

0 42Kilometers

162000 166000 170000 174000 178000 182000 186000 190000 194000 198000

Piezometric Level

CentersBorehole

Temp GradientContour

40

50

60

70

80

Lake Baringo

prospect

• Orientation of high temperature areas is NW-SE

• Lake located on a fault.

• Total heat loss from the prospect is > 1049 MWt

• Conduction

– 941 MWt

– 90% of the conductive heat loss occurs along the fault zones

• convection– 108 MWt by (105 MWt is

lost in Kokwa Island)

Korosi and Chepchuk

• Korosi is a central volcano

• Extends to North of Baringo

• Has wide distribution of

surface manifestations

• Paka is a caldera north of

Korosi

• Surface manifestations cover

about 45 km2

Korosi &

Chepchuk

Eastings

Tanglubei

Paoyi

Riongo

Loruk

Chesirimion

Chemiril

Kadogoi

Cepkalacha

Komolion

1

2

3

45

6 78

9

10

11

12

13

14

15

16

1718

19

2021

L Baringo

OlKokweisland

°C

Legend

Craters

Contours

Roads

Paka Craters

Lake Tulam

0 42Kilometers

162000 166000 170000 174000 178000 182000 186000 190000 194000 198000

Piezometric Level

CentersBorehole

Temp GradientContour

40

50

60

70

80

Korosi and Chepchuk

• Heat source at Korosi is

controlled by NE-SW and

NW-SE trending faults.

Conduction

– About 2,135 MWt Korosi

– About 546 MW at

Chepchuk.

Convection

• 0.4 kWt

• Almost all the heat lost is

by conduction

Lake Baringo

Chepchuk

Korosi

Paka prospect

• Associated with a central

volcano

• Study covered 500 km2

• Heat loss features are hot

grounds, fumaroles,

steaming grounds

• Located in & around the

caldera

Heat loss features covered

32 km2

Max. temperature 93oC

Paka

Paka prospect• Heat loss features

display NE-SW &NW-

SE trend

• Conductive heat loss

is 2,655 MWt

• Convective heat loss

is 10 MWtLake Baringo

Eastings

Tanglubei

Paoyi

Riongo

Loruk

Chesirimion

Chemiril

Kadogoi

Cepkalacha

Komolion

1

2

3

45

6 78

9

10

11

12

13

14

15

16

1718

19

2021

L Baringo

OlKokweisland

40

50

60

70

80

°C

Legend

Craters

Contours

Roads

Paka Craters

Lake Tulam

0 42Kilometers

162000 166000 170000 174000 178000 182000 186000 190000 194000 198000

Temp Gardient Contours

CentersBorehole

Paka

Korosi &

Chepchuk

Temperature & hydraulic

gradient

• Bore holes indicate

230oC/m near the active

zone of the prospects

• Cold areas indicate

0.02oC/m

• Water flow is from east &

west and from south to

north

Eastings

Tanglubei

Paoyi

Riongo

Loruk

Chesirimion

Chemiril

Kadogoi

Cepkalacha

Komolion

1

2

3

45

6 78

9

10

11

12

13

14

15

16

1718

19

2021

L Baringo

OlKokweisland

40

50

60

70

80

°C

Legend

Craters

Contours

Roads

Paka Craters

Lake Tulam

0 42Kilometers

162000 166000 170000 174000 178000 182000 186000 190000 194000 198000

Piezometric Level

CentersBorehole

Temp GradientContour

Paka

Korosi

Baringo

Chepchuk

Ranking based on heat lossProspect Heat loss Total heat loss

(MWt)Conductive

(MWt)

Convective

(MWt)

Menengai 1095 2440 3536

Paka 2845 10 2855

Korosi 2135 0.4 2135

Bogoria 762 437 1199

Baringo 941 108 1049

Chepchuk 546 Negligible 546

Arus 467 .03 467

Olkaria 400

Domes 187

160 180 200

Eastings (km)

-20

0

20

40

60

80

100

Nort

hin

gs (

km

)

40

50

60

70

80

°C

PakaCaldera

ChepchukKorosi

L Baringo

L Bogoria

Arus

Ol Banita

MenengaiCaldera

KinyachCrater

Equator

Paka Prospect

Menengai Prospect

Menengai to Paka

• Heat loss features

display NW-SE and

NE-SW trend

• L. Bogoria and L.

Baringo heat loss

features are NW-SE

• Korosi heat loss

features are oriented

in NE-SW

Heat loss and other disciplines

• Assists in quantifying amount of heat being lost naturally by the prospect

• Complements other disciplines in determining the reservoir temperature

• Assists other disciplines in identification of active structures

• Suggests possible orientation of the fracture zones