TERRESTRIAL HEAT FLOW STUDIES AND INVESTIGATIONS OF GEOTHERMAL RESOURCES IN INDIA

Abstract

As la veil known* the earth is a great reservoir of thermal energy which continuously flows outward towards 20 ito surfaoe at the rate of about 3.1 * 10tv calories per year* which is considerably larger than the total energy annually released through volcanoes and earthquakes. Occassionally* tale la manifested at the surface In the font of hot springe geysers* fuaarolee and voloanio eruptions. Oeothermal studios shed significant light on the evolution of the earth and the nature of hoat and mass transfer In Its interior and various other deep seated processes. In recent years they have attracted consider* solo attention owing to their diagnostic value in delineat ing plate kinematics sad hot spotsi la particular* reglone of anomalously high goohoat whioh could bo exploited as a repleaishable resource la an increasingly power hungry world. Investigations aimed at studying the thermal state of the cruet la the Indian subcontinent through investigations of terrestrial heat flow at a largo auaber of carefully aoleeted loeatlons^and exploration of the goothermal resources of some of its hot spring areas forme the subject matter of this thesis* Results of these investigations and their analysis, nyntbesised with A-1 other geodata especially generated for this study as well as that already available are discussed* IAL HBAT F&OW STTJDXB8 Beat flow determination involves accurate raeasuremsnt of subsurface temperature gradients at various depths in boreholes and a detailed study of tho thermal conductivity of ooncemod rooks. Equipment used for these asasurements were specially designed and fabricated for this purpose. Those are briefly described in tho thesis. Beat flow values including thermal logging data obtalaod la a largs number of boreholes at various locations in tho following tectonic units of tat Indian subcontinent are discussed, as well as values of the coefficients of thermal conductivity of rooks. 1. The Carabe* baaia 2. The Koyna region 5, The Aravalli Mountain Bolt 4* The Dharwar Sehist bait Terrestrial hoat flow values thus obtained in various parts of tho Indian subcontinent show considerable variations which may bo summarised as followst • Tho Dharvsrs and the areas covered with the rooks of Aravalli sad Pre-Aravalli Super Groups are characterised with low hoat flow values <*C 0*95 HFD*) A-2 3 aa are tho Deocan Traps which most probably over- He the eroded shield rooks of low radioactivity, the Upper Mantle temperatures under low heat flow areas of the Indian Shield being most likely around 400*0* • Proterozoic aiogeemynoliao bolts and areas of platform deposits ore distinguished la their thermal character by slgnlfloanUy higher heat flow values of 1*7 HPO*. • Tho part of the Caabay basia looatei towards the north of the Kshi river also shows high hoat flow values of 1*8 - 2*3 HFTT, the main eauso for which r appears to be the transient thermal perturbations produced by aa extensive Injection of basaltic material la the crust during the upper Miocene- Pliocene times* Besides, an analysis has also been attempted of the various Preosmbrlan shields of the world which are generally found to bo associated with low heat flow values* Some anomalously high beat flow values havs beoa obeerved la the Indian (Aravalli, Cuddapah basin ate*) as well ss la other shield areas* These variations apparently related to the evolutionary history of shields sad shield segments, when examined for their global occurrences* appear to suggest thst the Eurasian Shields are generally associa ted with lower heat flow values than those of tho Goadwsnaland. 1 HFU - lor^cal.om^.see*1 8 41.87 sM a"2. A-3 Tho results of heat flow Investigations hove been further discussed la respect ofsoma peninsular re ions* la tho light of their kaowa geology, tectonics and near surface concentration of heat generating radioactive elements* such aa was available* There mpp^w to bo lateral variations in the cub-surface temperatures within tho ilthoephore underlying the Indian shield and these may cause thermal stresses responsible for soae of the seismic activity along aa ancient zones of weakness. BWWBMTXOB OP GSOTSCiaTCCAl, RSS0URC3S Xadla is a subcontinent with a large population, where local conditions and availability of natural resources vsry greatly from one region to another, particularly of energy resouroeo which constitute a crucial Input for economic and social development* The only way to provide energy to every corner of the country, whether in the inhospitable desert regions or la the remotest regions of perennial snows, without wastage sad without degrading the environment, is to develop and exploit reploneohibls sources of energy* leothorial resources belong to this unconventional group. Attempts to explore and develop geohest sources both of the natural hydrothormal systems in hot spring regions and also of dry hot rooks, have boon initiated in a number of countries and intensified A-4 0 5 la others where some exploration was already in progress. In order to gala a batter insight into the goothormal recourses of India and to recognise, if possible, certain goothormal provinceo where subsurface thermal waters may be encountered and exploited, aa analysis and synthesis has boon attempted of available geodata particularly of the surface zxmifestations of goohost and available heat flow data in tho Indian Peninsula In the light of the major tectonic features* It is felt that non-voloanio goothormal resouroeo of moderate and low grades oan be expected to occur la certain goothormal provinces of India* Pursuing encouraging results of ths reconnais sance work for goothormal exploration In the Page valley (Ladaka), detailed investigations were planned and carried out to establish tho character and extent of tho geotheraal sources of ths valley* Ths results of geo* theraal investigations so obtained i.e., estimation of the natural heat loss from the surfaoe, probable reservoir temperature, sub-surfsee thermal conditions, structure of the Puga valley and its )ower potential, as well as their analysis is contained in a later chapter of this thesis. Additionally, results of some Investiga tions in tho Parbatl vallsy (Manlkaran-ICasol) hot spring ^•ae* ^amm •m^m>v ^* w#a^^^ w^%r v.. •*aaw*f** %sas>ar**arm) .'-5 while summarising the asln results of the present study, some problems of basic and applied nature have also been deilae ted which need to bo investigated in further detail • Suggestions have also been included for more detailed exploration la the promising areas*