AN APPRAISAL STUDY ON THE GEOTHERMAL POTENTIAL OF THE KENYA RIFT

PROJECT IN GEOLOGYSGL 413.PRESENTED BY: EDGAR NAMBIRO

SUPERVISOR: Dr. MULWA

OUTLINE

INTRODUCTION GEOLOGY EXPLORATION GEOTHERMAL PROSPECTS CONCLUSSION RECOMMENDATION

INTRODUCTION

The Kenya rift lies in the greater East Africa Riftsystem.

The rift forms along an ancient suture zone splitsthe Africa into two new tectonic plates: Somali andNubian Plates.

Kenya rift lies along the Eastern arm of the EARS. The rift forms a narrow zone in where the African

Plate is in the process of splitting into two newtectonic plates, the Somali and Nubian Plates.

SETTING The Great East African Rift System

(EARS) is one of the major tectonicstructures of the earth that extendsfor about 6500 km from the MiddleEast (Dead Sea-Jordan Valley) in theNorth to Mozambique in the south.

This system consists of three mainarms: the Red Sea Rift; the Gulf ofAden Rift; and the East African Rift.

The eastern branch of the EARS,that forms the Ethiopian andKenyan rifts, possesses, by far, themost extensive geothermal resourcebase in Africa and one of the mostextensive in the world.

The main stress points punctuate the rift, the major point of stress isthe uplift zone and two other stress points of rift bifurcation. TheEARS rifting is believed to have preceded or coincided with dormaluplift.

Origin of the rift can be summarized by two models: an active andpassive model. Active mechanisms – Ascending mantle convection thins the

lithosphere causing crustal doming and lithospheric failure. Theplume flow thins the lithosphere causing isostatic uplift.

Passive mechanisms – Pre-existing tensional stresses causefailure. Crustal doming and volcanism are secondary processes.The lower density asthenosphere rises passively resulting in alarge regional uplift.

Domal uplifts are distributed throughout the African plate whichcame to rest with respect to the mantle plume dated 25Ma. Thehotspot caused doming in 3 major ways; Conduction and thermalexpansion of the lithosphere, Injection of hot magma into thelithosphere and Diapiric up rise of asthenospheric material into thelithosphere.

It appears as if these large-scale intrusions beneath theKenyan and Afro-Arabian domes are not continuous. Therift evolved by fault propagation above a single regionalintrusion due to localised thinning and uplift at the centre

The eastern arm of EARS evolved in three major pulses.Quaternary age activity has been generally acceptedacross the board and this is what will be mainly usedthroughout this report. These volcanic centers are the heatsources for the geothermal systems subsurface reservoirs

If the major thermal fields along the rift were considered,we derive three areas of high thermal activity; the LakeTurkana Group, Olkaria Group, and Natron-North Tanzaniagroup.

SETTING Penetrative convection cells developed

beneath the major dome of Kenya Riftand based on the Elder’s model, thisinform of a continuous heat flow over ashort length forming end cells at theedge of a heat source evolving into aprimary central cell flanked by twosecondary cells.

If the major thermal fields along the riftwere considered, we derive three areasof high thermal activity; the LakeTurkana Group, Olkaria Group, andNatron-North Tanzania group.

Major geothermal regions are superimposed on the map. T = Turkana; B =Bogoria; E-Eburru; 0 = Olkaria; M = Magadi ; N = Natron.

OBJECTIVES

Examine the Geothermal Potential different geothermal prospectus fields in detail along the Kenya rift.

Numerous researchers’ and organizations have given conflicting values on the energy potential of the Rift generally ranging from 3000 – 14000 MW. It is for this reason that I chose to examine the Kenya Rift geothermal resources and arrive to an accurate value.

Utilization of geothermal fluids. The high enthalpy and high cyclic discharge wells that are currently being underutilized at Olkaria losing about 186MWt to the atmosphere.

Possibility of employing enhanced geothermal system (EGS) within the rift.

JUSTIFICATION

Growth in Electricity Demand. Recent effects of drought that have rendered

hydro power unreliable. Silting of hydropower resources. Volatile nature of Petroleum prices.

METHODOLOGY

Mainly focus on Literature review and draw a conclusion from the exploration results gathered over time on the prospects.

GEOLOGY AND THE GEOLOGICAL SETTING The rift valley is made up of a series of normal and reversed faults

bordering a trough funneling out towards the north in Afar HighlandsEthiopia.

Kenya rift diverges into splays towards the South and the North inTurkana. Dormal uplift and extensions caused the brittle crust tofracture into a series of classic horst and graben structures.

Sequence of events between doming, rifting and alkalinemagmatism/volcanism is detailed below. Early to Mid-Miocene – Early Uplift. (Incipient melting of the upper mantle.) Upper Miocene – Doming about 300m. Down warping at future rift

shoulders. Fissure eruption resulting to Basalts and Phonolites. Pliocene – Doming about 1400m. Main rifting occurs forming a graben due

to faulting ~Trachyte outpour. Quaternary – Major graben formed and continued faulting occurs. Caldera

volcanoes form in the axial zone. (Shield volcanoes development)

GEOLOGICAL MAP OF KENYAThe Kenya Rift system canbe seen in the mapbounded by the fault lines.There occurs branchingforming the Kavirondo Rift.Generally the Rift isbounded by the Mau andAberdare escarpements.A bourger gravity anomalyexists regionally along therift believed to be thesource of the geothermalactivity.

Geothermal activity in the Kenya rift manifests itself by occurrence of volcanoes, fumaroles, boiling pots & steaming grounds, geysers and sulphur deposits.

Using today’s technologies, Eastern Africa has the potential to generate more than 15,000 MW of energy from geothermal power.However, only 214MW is currently generated in Kenya (209MW) and Ethiopia (5MW).

GEOTHERMAL RESOURCES IN KENYA `

The high temperature geothermal resources are closely related to the volcanic centres, both at the pre caldera stage (Korosi) and in particular their calderas.

Geophysical data support the concept that a diapir of relatively low density material is situated below parts of the rift system.

seismic refraction and gravimetric data suggest the presence below the Kenya rift of a low density body of 3.15 g/cm³ and P wave velocity of 7.5 km/s from 20 to 60 km depth and a lateral extent of 200-250 km wide.

In the Eastern Rift seismic activity seems to be more concentrated in swarms of certain areas.

GEOTHERMAL EXPLORATION TECHNIQUES Based on detailed understanding of the subsurface.

They include: Geology (lithology, geochronology, structures); Geophysics (seismic, gravity, magnetic, and resistivity); Geochemistry (fluid and thermometry), Heat flow assessments.

Geothermal reservoirs are closely associated with heat flow systems rather than lithology.

volcanic center: the area with the highest volcanic production, the greatest rock variety and where a caldera has formed.

A geothermal system is made up of four main elements: Heat Source, Reservoir, Carrier Fluid and Recharge

zone.

Reservoir ModelsNormal - The hottest part of the subsurface resource lies directly below the visible surface manifestations.Hidden – Lateral displacement by a few kilometers of the primary deep thermal anomaly from the geothermal activity surface evidence.

Prospect ReconnaissanceSurvey

Surface exploration AppraisalDrilling

Olkaria I,II & III Completed Completed Done

Olkaria IV Completed Completed Ongoing

Eburru Completed Completed Done

Longonot Completed Completed Not Done

Suswa Completed Completed Not Done

Menengai Completed Ongoing Ongoing

Badlands Completed Ongoing Not Done

Lake Magadi Completed Ongoing Not Done

Gilgil-Kariandusi Completed Ongoing Not Done

Arus Completed Ongoing Not Done

Lake Bogoria Completed Ongoing Not Done

Baringo Completed Ongoing Not Done

Korosi Completed Ongoing Not Done

Paka Completed Ongoing Not Done

Silali Completed Ongoing Not Done

Homa Hills Done Ongoing Not Done

DISCUSSION Heat from the molten mantle is conducted to adjacent rocks and through

convection it in turn transferred to underground water reservoirs. Utilization of the geothermal fluid is dependent on the thermodynamic

characteristics (temperature or enthalpy) and chemistry of the fluid. Thetable below shows the classifications proposed by different authors.

Based on enthalpy the geothermal fluid can be utilized in different wayselectricity generation being the most important.

RESULTSVolcano Name Type of

VolcanoLast Activity Gas Thermometry

Temperature 0CGeothermal PotentialMWe

Barrier Shield Holocene 100

Namarunu Shield 200 20*

emuruangogolak Shield 200-350 200

Silali Shield 238-287 1200

Paka Shield 250

Bogoria Shield Pleistoce 145-245 20*

Korosi Shield Holocene 250 100

Menengai Shield 250 1650

Eburru Complex Holocene 300 50-60

Olkaria Pumice Cones

1000

Longonot StratoVolcano

300 100

Suswa Shield Volcano

Holocene 250 250

Lake Baringo 120-220

Chepchuk 10-20

GEOTHERMAL POWERPower Station Power Output Initial out put Projected

expansionOlKaria I 45 MW - 285Olkaria II 105 MW 70 -Ormat Inc 50 MW 12 100Oserian 4 MW 2 -Olkaria IV 140

0

200

400

600

800

1000

1200

1400

1600

1800

Geothermal Potential MWe

GeothermalPotential MWe

The only commercial application of geothermalenergy for other uses other than electricitygeneration (direct applications) in Kenya is atOserian.

Other minor geothermal direct uses are at LakeBorogia hotel, where a geothermal hot spring isbeing used to warm a swimming pool and atEburru geothermal resource where the localcommunity uses geothermal energy for dryingfarm produce mainly pyrethrum.

DISCUSSION

Emphasis when determining geothermal prospects should be on the Volcanoes: Structure, Eruption phenomena & Composition.

The Geothermal Potential is based on the location of the Magma Chamber.

Significant emphasis is also placed on geochemistry: relate the magma chamber dynamics to the volcanic rocks.

Its worth noting that the major prospects along the rift occurred in calderas. This can be related to the size of the magma chamber where cooling models can be used to predict the residual heat.

CONCLUSSION

Kenya Rift has a large untapped geothermal resourcepotential that are associated with volcanic centersspread along it.

From the detailed studies carried out in all thegeothermal prospects its clearly that the geothermalpotential of the rift is enormous and ranges between6000 – 15000 MW as projected by UNEP and GDC.

In the Kenya Rift, the Central Group (Olkaria) is the most promising prospect with of them all.

After completion of Olkaria IV, upgrading of Olkaria I and Orwa Power Inc., the Olkaria resource would be producing 575 MWe.

The resource is an indigenous, environmentally clean andeconomically viable, renewable energy resource;

Development of geothermal resource is constrained by (i) the risks that are associated with resource exploration and

development; (ii)the financial risks that are associated with investment in power

development projects ; and (iii) lack of appropriate investment and institutional settings in

many East African countries;

Diversified use of energy augments energy supply fromhydro power plants and improves the generation mix. Itavoids vulnerability to drought and oil price fluctuations.

RECOMMENDATION

Data resource centers should be set up as most of the workdone in the area is held in confidence.

Loans and grants from International Organizations to financethe projects for further exploration and development;

Private Sector participation and financing from developers ,investors, equipment suppliers and development banks.

Establish long-term conducive policies and incentives thatattract private investment;

Establish a Risk Guarantee fund by donor and developmentagencies for exploratory and appraisal drilling of projects;

Set up a Regional Network of Geothermal agencies to ensurethe promotion and use of geothermal expertise in the EastAfrica Region. (ARGEO)

THE END