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Geothermal surface manifestation mapping in south western
- 1. Geothermal Surface manifestationmapping in South-Western Tanzania Mnzava Lightness J., Mayo, A. W. and Katima J. H.Y. University of Dar es Salaam -Tanzania College of Engineering and Technology (COET) DAR ES SALAAM ARGEoC2. 24-25 NOV. 2008 ENTEBBE-UGANDA
- 2. CONTENTS 1. INTRODUCTION 2. GEOTHERMAL SURFACE MANIFESTATATION AND SRING SURFACE TEMP. 3. WATER TYPE 4. FLUID MINERAL EQUILIBRIA-SUB-SURFACE TEMP 5.POTENTIAL USABLE HEAT AND POTENTIAL POWER ESTIMATES 6. CONCLUSION AND RECOMMENDATIONS 7. WHAT NEXT?.
- 3. UNITED REPUBLIC OF TANZANIA • Location: East Africa lat. 1°S to 11°45´ S and long. 29° 21´E to 40° 29´ E • Population: 34.6 M(2002) • Size: 945,087 Km2 • Percapita energy consumption 0.7 ToE (tonne of oil equivalent)
- 4. UNITED REPUBLIC OF TANZANIA Physical features -A land of plenty from wildlife, forests products, minerals (gold, tanzanite, emerald and diamonds etc) gas, solar, Wind and geothermal; - with African’s highest mountain (Kilimanjaro) at 5,895m and lowest point (lake Tanganyika) at 358m below sea level - Spectacular lakes; Tanganyika, Nyasa, Natron, Manyara and Eyasi in the East African Rift valley, bounded by fault scarps
- 5. General geology Dominatedby a large mineralized Precambrian craton with formations of >2 bil yrs old, rimmed by Proterozoic crystalline rocks. Younger sediments and volcanoclastics of recent, occupy the rifted graben, coastal plains and inland basins
- 6. Electricity Generating capacity(2006): 1018 MW 72.3% owned and operated by TANESCO Hydro 561 MW Natural gas 182 MW Diezel IPP 100 MW Isolated 10 towns (decentralized) 55.5 MW Other IPPs 41.5 MW Imported (Zambia and Uganda) 13 MW Comsumption: 46 kWh/capita per annum Access to electricity 11.5 % of population Rural population access to electricity 2% Geothermal -
- 7. Geothermal sites inTanzania the studied area and the selected GEOTHERMAL project region There are more than 15 locations, with more than 50 hot springs of temp > 40°C; - Some are found over and near the active rift segments within Quarternary volcanism and in Pre-cambrian craton
- 8. Potential locations ARUSHA Natron- Manyara MBEYA Rungwe LOCATION OF MOST POTENTIAL GEOTHERMAL SITES IN TANZANIA Estimated Potential 560 MWe (1981)
- 9. Mapping surface manifestationsin South western Tanzania, • Geothermal mapping of surface manifestations, which includes structural mapping and hydrothermal mapping was carried out in the four geothermal prospects of South-western Tanzania namely Songwe, Mapulo-Kasimulo, Rungwe and Lake Ngozi area.
- 10. Fig 1: Simplifiedgeological map showing the triple junction, location of the study area, in the Rift valley
- 11. Field work •Springs in the three different prospects were mapped (Fig.3.1, 3.2 and 3.3) • different parameters such as temperature, flow rate, altered rock, mud pools, sulphur, artesian springs and structure setting of the springs were observed and recorded. • Water samples were collected
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- 15. Surface spring maximumtemperatures encutered • Rungwe 98oC at Makwehe geyser • Ngugwisi river springs 86oC • Songwe springs and Malonde 85oC • Mampulo and Kasimulo 65oC • Lake Ngozi 65oC
- 16. Surface manifestation Plate4.1: Songwe-Bwana Hutu hot ground
- 17. Vegetation zonation Plate4.2: Mampulo hot ground showing vegetation zonation
- 18. Fracture spring Plate4.3: A fracture controlled spring, steam rising along the fracture from the boiling water within
- 19. Intermittent discharge; geysers Plate 4.4: Makwehe-Rungwe geysers with steam rising at the top left corner of the photograph
- 20. Water type Fig.4.1Classification of water type by Cl-HCO3-SO4 ternary diagram
- 21. Fluid mineral equilibriaand subsurface temperatures Fig. 2: The (Na+- K+-(Mg+2)1/2) ternary diagram for Dec. 2002
- 22. Tkn temperatures fromthe ternary The temperature given by tkn in the diagram were around • 220oC Rungwe; • 210oC Songwe; • 209oC Mampulo and • 180oC Kasumulo
- 23. Heat stored, Potentialstored heat and the Power potential of the prospect • From the literature it was reported that the prospect have a temperature of 270oC (SWECO-VIRKIR, 1978), • therefore this was used as the maximum temperature in the calculation of a rough estimate of heat stored • in rocks, fluid, vapor and condensate; • potential stored heat and • power potential of the prospect:
- 24. Potential usable heat • Potential usable heat = Ql + Qv + Qc • = 0.27 x 1018J + 0.014 x 1018J + 2.24 x 1018 J • = 2.52 x 1018J.
- 25. P MWe Potentialusable heat * re cov ery factor * efficient conversion factor ⎤ ⎡ = ( ) ( ) ( ) ( ) ( ( )) ...............(4.9) Lifetime yr * days per year * hours per day *sec onds per hour ⎥⎦ The Songwe prospect Power Potential ⎢⎣ • The assumption was made that • the resource have a life span of 25 yrs, • a recoverable factor of 0.25 and • an efficient conversion factor of 0.162.
- 26. Songwe prospect PowerPotential P MWe Potential usable heat * re cov ery factor * efficient conversion factor ⎤ ⎡ = ( ) ( ) ( ) ( ) ( ( )) .......... ..... (4 .2 ) * * * sec ⎥⎦ ⎢⎣ Lifetime yr days per year hours per day onds per hour 18 ⎤ ⎡ = P MWe 2 .52 x 10 x 0 .25 x 0 .162 1 .07 10 8 / ( ) x (J s ) x x x 25 365 24 3600 = ⎥⎦ ⎢⎣ = 107 x 106 (J/s) = 107 MWe
- 27. Conclusion and Reccomandation • From these preliminary studies of surface manifestations it shows that the South-Western Tanzania prospects have a prospective geothermal potential with surface maximum temperature range of 65oC-98oC • Subsurface temperatures maximum ranging between 180oC-220oC (tkn) • An estimated power potential of the Songwe prospect is about 107 MWe. • It is recommended that further work for developing the resource should be taken into consideration.
- 28. What Next? •So far, the highest potential prospect for geothermal power exploration is at the south-western Tanzania (the Rungwe volcanics and Songwe/Rukwa basin) • The study to identify exploratory drilling sites need a detailed exploration plan, intergrating geological, geophysical (TEM, MT, Gravity), fluid chemistry, isotopes and gases • Training in different kinds of geothermal displines to build geothermal human resources capacity • Move to appraisal studies and field development for more promising sites • Create awareness on geothermal • Conduct nationa-wide geothermal resource assessment for production of a national geothermal resource map • Facilitate international cooperation in geothermal development.
- 29. Acknowlegement • Theauthor acknowledges the assistance of: • Auckland University Geothermal Institute • UNU Iceland Geothermal Institute • KenGen Kenya • SIDA • University of Dar es Salaam-COET • MEM • Profesorial Chair of Energy and Technology UDSM
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