hdr prospects of himalaya geothermal...

D. Chandrasekharam: HDR PROSPECTS OF HIMALAYA GEOTHERMAL PROVINCE______________________________________________________________________________________

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Under the auspice of:Division of Earth Sciences

Chapter 3.7

HDR PROSPECTS OF HIMALAYAGEOTHERMAL PROVINCE

D.Chandrasekharam

Department of Earth Sciences, Indian Institute of Technology, Bombay, India.

Abstract:

A large data base on geological, geo-physicl and subsurface geological informa-tion on the wet hot rock geothermal pro-vinces is now available to exploit this energyresource. Besides wet hot rocks, HimalayaGeothermal province has excellent hot dryrock sites for future exploration and ex-ploitation. This province falls within the In-do-Tibet collision zone and sufficiently largeplutons occur within this zone which can beexploited for future energy needs of the sta-te. With participation of local governmentand investment from independent powerproducers, this energy source can developedto meet the energy demands of the hill ruralpopulation.

Introduction:

Nearly 70% of India's power productionis based on thermal because of the avai-lability of huge and inexpensive coal re-serves. Excessive use of this source withoutthe use of strategies to mitigate its effectswill have deteriorating effect on the qualityof human life in future. In another decadeemission of CO2, SO2 and Nx will exceed1500 million tones, 1900 kilo tones and1200 kilo tones respectively ( World BankReport 1999). This means CO2 emissionswill be 775 million metric tones per year as

compared to 1000 million metric tones peryear produced in the entire European Union!There is no doubt that the cost of electricityproduced from coal is far less expensivecompared with other fuels. The present daycost of one unit of power is less than US$0.02 in the case of coal based power whileliquid fuel based power costs about US$0.04 per unit (Mehta, 1999) and hydropower costs about US$ 0.03 (World BankReport, 1999). But the expenditure spent tomeet the consequences (like disposal of flyash; treating the high ask coal etc) is highwhich automatically increases US$ 0.02 aunit to little over 1 US$. Now a time hascome to look into those alternate energysources which were not viable a decade agodue to non availabilities of technical knowhow. At present 1.5 percent of total powergeneration capacity comes from non-con-ventional energy sources like wind, solarand bio-mass (Table 1; Chandrasekharam,2000a). In the next fifteen years, accordingto the world bank report (World Bank re-port, 1999), this energy supply could increa-se by seven times and above. India can notignore its huge energy resource availablefrom wet and hot dry rocks in future.

Hot Dry Rock Province:

International Seminar on HDR TECHNOLOGY______________________________________________________________________________________

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Out of the seven geothermal provinces,projects have been initiated to tap powerfrom the wet hot rocks from one of thecentral geothermal provinces (Tattapani) andserious consideration is being given to tapthis energy from other provinces. Besideswet rocks, Indian geothermal provinces haveexcellent sites to initiate hot dry rockprojects.

The three important criteria a site shouldsatisfy to be HDR prospect are a) a sub-stantial mass of hot rock should be availableat a reasonable depth, b) the region withsuch mass of hot rocks should be undercompressional stresses and c) this hot rockshould have a insulating cover above tosustain the heat generated by the radioactivedecay of U and Th.. There is one suchexcellent province, the Himalaya geothermalprovince which satisfies all these conditions.This paper examines the geological,geophysical and tectonic aspects of thisprovince.

Figure 1 shows all the sub-provinces inthe Himalaya. These provinces lie parallel tothe Indo-Asia collision zone (Main CentralThrust and Indo-Tibet Suture Zone). Theentire geothermal province covers an areagreater than 1500 sq.km. The heat flowvalue varies from 70 - >180 mW/m 2 (Fig.2). The thermal waters issuing in thisprovince record temperatures as high as 98oC and some times are associated with highsteam content (Chandraekharam, 2000 b).The geothermal gradient recorded from shal-low bore-wells is greater than 100 oC/km.Such high heat flow and geothermal gradientare due to high radioactive elements presentin the granites and also due to the presenceof seismic bright spots (discussed below) inthis region. The Himalaya geothermalprovince falls within the Asia-Indian platecollision zone and the main central thrust(MCT) passes through this geothermal pro-vince (Fig 1). Besides Precambrian and sedi-mentary formations related to the fore-arcbasin, this provinces encloses a large num-ber of granite intrusives (Fig. 3) which varyin age from 60 to 5.3 Ma (Schneider et al.,1999a,b; Searle, 1999a,b; Le Fort and Rai,1999; Haris et al., 2000; Harrison et al.,

1998, 1999). These granites are exposed onthe surface at several places and are coveredby sedimentary formations at several places.These granites occur as lopoliths, sheets anddykes (leucogranites) which vary in thick-ness from a few meters to several kilome-ters. Permian Granites of 268 Ma also occurin the western Zanskar (Noble et al., 2001).International Deep Profiling of Tibet and theHimalayas (INDEPTH) project located seis-mic bright spots in Tibet region (east of theIndian Geothermal provinces) which are at-tributed to the presence of magmatic meltsand or saline fluids within the crust (Makov-sky and Klemperer, 1999). Highly saline flu-ids are also found in Ladakh granites (~60Ma) as inclusions which are attributed to thehigh volatile content in the granitic melts(Sachan, 1996). Though INDEPTH investi-gation has not been carried out, consideringthe proximity of INDEPTH site in Tibet,probability of occurrence of such seismicbright spots within the Himalayan geother-mal province is high. This inference gainsstrength from the 1 Ma anatexis processrecognized in Nanga Parbat (Chichi granitemassive) in Pakistan Himalayas (Schneideret al., 1999 c) and similar processes must bein operation on the eastern side of NangaParbat also. These evidences confirm thatthe present day observed high heat flowvalue (>100 mW/m2) and geothermal gra-dient is related to crustal melting process atshallow depth in this region.

Regional stress analysis based on earth-quake focal mechanism, bore-hole blow-outs and hydrofracturing (Gowd et al.,1992)indicates that the entire Himalayan belt ingeneral and the Himalayan geothermal pro-vince in particular, is under compressivestress regime due to the northward move-ment of the Indian plate and net resistiveforces at the Himalayan collision zone. Thusthe central and northern India includingNepal, the Great Himalayas and Pakistanfall under this stress province characterizedby NNE-ENE oriented SHmax (Fig.4). Inves-tigation carried out around Zanskar (north ofKulu, in the Himalayan Geothermal provin-ce) by Pierre Dèzes (1999) also shows com-pressive regime in this region (Fig.5). Com-


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pressional stress regime is favourable tocreate several sub-horizontal reservoirs ingranites by hydrofracturing, interconnectedby boreholes ( Baria et al., 1999; Wyborn2001).

The entire subduction tectonic regimealong the Himalayan geothermal provinceappears to be similar to Hijiori and Kansaiprovinces in Japan where HDR prospect isbeing evaluated. International HDR feasi-bility study can be initiated in this regionwith Local Himachal Pradesh Govt. supportand support from the independent powerproducers.

With the present trend of globalization,incentives given to non-conventional energypower producers, problems in establishingpo-wer grid in the hilly terrains of Himala-yas and environmental problems associatedwith coal based power projects, the future ofHDR prospects in this geothermal provinceis very promissing.

Reference:

Baria, R., Baumgartner, J., Rummel, F., Pine,R.J. and Sato, Y. 1999. HDR/HWR reser-voirs: concepts, understanding and cretion.Geothermics, 28, 533-552

Chandrasekharam, D. 2000a. Geothermal energyresources of India- Opportunities for IPPs.Proceed. Geothermal Power Asia 2000Conference, Manila, Philippines. February,2000. 10p

Chandrasekharam, D. 2000b. Geothermal energyresources of India- Country update.Proceedings, World Geothermal Congress2000, Japan. (Edts) E. Iglesias, D. Black-well, T.Hunt, J.Lund, S.Tamanyu and K.Kimbara. pp- 133-145.

Gowd, T.N. and Srirama Rao, S.V. 1992. Tecto-nic Stress Field in the Indian Subcontinent.J.Geophy.Res., 97, 11,879-11,888.

Haris, N., Vance, D. and Ayres, M. 2000. Fromsediment to granite: timescales of anatexis inthe upper crust. Chem. Geol., 162. 155-167.

Harrison, T.M., Groove, M., Lovera, O.M. andCatlos, E.J.1998. A model for the origin ofHimalayan antexis and inverted metamor-phism. J.Geophy. Res., 103, 27,017-27,032.

Harrison, T.M., Grove, M., McKeegan, K.D.,Coath, C.D., Lovera, O.M. and Le Foort, P.1999. Origin and episodic emplacement of

the Manaslu intrusive complex, CentralHimalayas. J.Petrol., 40, 3-19.

Le Fort, P. and Rai, S.M. 1999. Pre-Tertiary fel-sic magmatism of the Nepal Himalaya: rec-ycling of continental crust. J. Asian EarthSci., 17, 607-628.

Makovsky, Y. and Klemperer, S.L. 1999. Mea-suring the seismic properties of Tibetanbright spots: Evidence of free aqueous fluidsin the Tibetan middle crust.J.Geophy. Res.,104, 10,795-10,825.

Mehta, A.1999. Power Play, A study of theEnron Project. Orient Longman Pub. Com.,New Delhi. 226 p

Noble, S.R., Searle, M.p. and Walker, C.B. 2001.Age and tectonic significance of Permiangranites in Western Zanskar, High Hima-laya. J.Geology, 109, 127-135.

Pierre Dèzes.1999. Tectonic and metamorphicEvolution of the Central Himalayan Domainin Southeast Zanskar (Kashmir, India)".Ph.D. Thesis. Université de Lausanne,Switzerland.

Sachan, H.K. 1996. Cooling history of subduc-tion related granite from the Indus Suturezone, Ladakh, India: evidence from fluidinclusions. Lithos, 38, 81-92.

Schneider, D.A., Edwards, M.A., Zeitler, P.K.and Coath, C.D. 1999a. Mazeno Pass plutonand Jutial pluton, Pakistan Himalaya: ageand implications for entrapment mechanismof two granites in Himalayas. Con. Min.Pet.,136, 273-284.

Schneider, D.A., Edwards, M.A., Kidd, W.S.F.,Asif Khan, M., Seeber, L. and Zeitler, P.K.1999 b. Tectonics of Nanga Parbat, westernHimalaya: Synkinamatic plutonism withinthe doubly vergent shear zones of a crustal -scale pop-up structure. Geology, 27, 999-1002.

Schneider, D.A., Edwards, M.A., Kidd, W.S.F.,Zeitler, P.K. and Coath, C.D. 1999 c. EarlyMiocene anatexis identified in the westernsyntaxis, Pakistan Himalaya. Earth. Planet.Sci. Lett., 167, 121-129.

Searle, M.P. 1999a. Extensional and compres-sional faults in the Everest massif, KhumbuHimalayas. J. Geol. Soc. London, 156, 227-240.

Searle, M.P. 1999 b. Emplacement of Himalayanleucogranites by magma injection alonggiant complexes: examples from the ChoOyu, Gyachung Kang and Everest leuco-granites (Nepal Himalaya). J. Asian EarthSci., 17, 773-783.


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World Bank Report 1999. Meetings India's fu-ture power needs: Planning for environmen-

tally sustainable development, The WorldBank, Washington DC, USA. 28 p

Wyborn, D. 2001. Personal communication.

Table 1. Power production status of non-conventional energy in India

Renewable Power Potential Achieved--------------------------------------------------------------------------------Wind Power 20,000 MW 1,000 MWSmall Hydro Power 10,000 MW 172 MWBiomass 20,000 MW 141 MWSolar photo-voltic Power 20 MW/sq.km 810 KW

Figure 1. Geothermal Sub-provinces of Himalaya. MCT: Main Central Thrust; ITSZ: Indo-Tibet Suture Zone.


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Figure 2. Heat Flow zones of Himalaya geothermal province.

Figure 3. Granite intrusives (with ages) of Himalaya geothermal Provice.

Figure 4. Stress field distribution in the Himalaya geothermal province.


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Figure 5. Cross section of Indo-Tibet Thrust Zone (at Zanskar). HHCS: High Himalaya Central Suture.

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