EXPLORATION HISTORY of OLKARIA using GEOPHYSICS

By Mariita N.O. 0 0 0 0 34 E 36 E 38 E 0 5 N 5 N

0 0 4 N 4 N

The Rift 0 0 Location 2 N 2 N

0

0 0 0 0

0 0 1 S 0 0 1 S 0 0 0 33 E 34 E 36 E 38 E 39 E 38oE North Island 4oN L. Turkana ETHIO PIA Central Island H u ri

Location of South Island Cenozoic Barrier Volcano Mesozoic volcanics sediments Olkaria UGANDA Emuruangogolak

Mt. Elgon Silale KKKKEEEENNNNYYYYAAAA within the L. Baringo Arus-Bogoria Nyambeni Kisumu o Rift Mt. O

Homa Hills Eburru L. Olkaria Longonot Suswa Mozambique metamorphic OLKARIA Ol'Esakut belt Olorgesaille L. Magadi 2oS 0 50 100 150 Shombole Kilometers Chyulu T Ol'Doinyo Lengai AN ZA Basalt-Trachyte-Rhyolite centers NIA Nephelinitic centers Alkaline centers Kilimanjaro Lakes Geothermal Prospects Geothermal Fields o o Rift Faults 36 E 38 E Olkaria manifestations

Fumaroles

Hot Grounds Kapedo Springs Silali Volcano

Discharge T=550 C 100 MWt produced from this spring alone Paka Volcano Olkaria chosen Exploration for geothermal resources in Kenya started in the 1950’s with mainly geological/geophysical (based on Resistivity/seismic) investigations between Olkaria and Lake Bogoria The exploration resulted in: the drilling of two wells X-1 and X-2 which encountered high temperatures at depth Olkaria and Environs….. Early Methods…. During the early stages of development Geophysical methods available included: Dipole Schlumberger Electromagnetic Head-on Gravity and Magnetics Seismics Various levels of success were achieved Geophysical investigations

• Geophysics = X-Raying the Earth

INVOLVES

• Sending signal into the earth • Monitoring natural signals from the earth Main GEOPHYSICAL METHODS used in Geothermal energy Exploration in Kenya •Gravity

•Resistivity

•Magnetics

•Seismic More work

Between 1973 and 1980 The exploration then gained momentum with support of the (UNDP) = more extensive geophysical investigations + additional wells drilled Resistivity…..most used

May indicate presence of reservoir and permeable structures (faults) – targets for drilling Resistivity signatures of Olkaria 100 Type 1

[a] Type 2

[c]

Type 4

10 [b]

[d] Type 3 Resistivity (Ohm-m) Resistivity

1 10 100 1000 10000 Depth (m) Resistivity distribution at 1400masl from TEM measurements

Ohm-m 9908000

100

Olkaria N-E 75 9904000 50

s Olkaria East

g

n i h 30

t Olkaria West

r o

N 9900000 Olkaria Domes 20

15

9896000 10

0

9892000 188000 192000 196000 200000 204000 208000 Eastings Resistivity data findings • Low resistivity (less than 20 m) anomalies at depths of 1000 m a.s.l. define the geothermal resource.

• The geothermal resource boundaries are controlled by linear structures in the NE-SW and NW-SE directions. Resistivity data findings…

• Some of the high resistivity regions coincide with recharge areas associated with NE and NW trending faults that act as conduits for cold water flow from the Rift Valley scarps.

• Fluid up-flow zones occur at the intersections of these regional faults in the vicinity of a heat source Other Geophysical methods

g.u. Gravity 9910000

-1650

9905000 Olkaria N-E -1750

s

g n

i -1850

h

t r

o Olkaria East N Olkaria West -1950 9900000 Olkaria Domes

-2050

-2150 9895000

-2250

190000 195000 200000 205000 Eastings Other Geophysical methods……

9910000 nT Magnetics 34000

9905000 Olkaria N-E 33875

s Olkaria East

g 33750

n

i h

t Olkaria West r

o 9900000 N Olkaria Domes 33650

33500 9895000

33350

185000 190000 195000 200000 205000 Eastings Other Geophysical methods…… Seismology Why Geophysics methods ???

Note: •All geophysical techniques are expensive, although some more than others •BUT still much, much cheaper than drilling Experiences/Trends in Geophysical Exploration at Olkaria • Experience shows: – Some methods are more suitable than others – Combination of several methods yields better interpretation – For siting of wells, there is need to incorporate other disciplines: Geology, Geochemistry – Information from the first exploration wells need to be used to review the initial geophysical model Experiences/Trends in Geophysical Exploration at Olkaria…. • NEWER equipments, faster computers, software have had to be purchased over the years.

• BETTER/EFFICIENT methods been deployed over the years. Experiences/Trends in Geophysical Exploration at Olkaria….

Example - Resistivity

Schlumberger –DC -Needs external current -Needs about 10 workers -Needs long cables > 8km Integrated Geophysical Model

INTERGRATED GEOPHYSICAL SECTION FROM TO LONGONOT THROUGH THE GREATER OLKARIA GEOTHERMAL FIELD

MAIELA OLKARIA E.P.F DOMES LONGONOT WEST 2000

0

-2000

200 )

. -4000 L

. HEAT SOURCE 100

S

. A

. 50

M ( 40 N HEAT SOURCE

O -6000 I HEAT SOURCE

T 30 A

V 20

E

L E -8000 15 10

5

-10000 0 188000 190000 192000 194000 196000 198000 200000 202000 204000 206000 208000 210000 212000 214000

EASTINGS LEGEND

Cold inflow Upflow Gravity High Micro-earthquake 0 5000 10000 hypocentres KenGen 2002 Olkaria and Environs Olkaria Geothermal Field Experiences from elsewhere • Many projects have had very long gestation periods: – Ohaaki, New Zealand - 25 years – Expanded Leyte Project, Philippines - 20 years – Olkaria 1 – 20 years – Olkaria II, Kenya - 17 years

• Within this time frame, actual construction time has been much shorter

• Time taken with, geoscientific study, exploration drilling, financing and approval processes Exploration status of other geothermal prospects Prospect Inception Report Surface Wells Sited Wells Studies Drilled Longonot Done Done Done Not Done Suswa Done Done Done Not Done Menengai Done Done Done Not Done Arus/L. Bogoria Done Done Done Not Done Korosi Done Done Done Not Done Paka Done Done Done Not Done Silali Done Not Done Not Done Not Done Emuruangogolak Not Done Not Done Not Done Not Done Namarunu Not Done Not Done Not Done Not Done Barrier Volcano Not Done Not Done Not Done Not Done Thank you !