The Geothermal Atlas of India describes some 340 hot spring sites and identifies more than 300 sites with geothermal energy potential in at least seven key geothermal provinces throughout India. About half of these sites are located in the Himalayan region, mainly in the northwestern sector where post-Tertiary granite intrusions are considered to be responsible for the high thermal gradients (>100°C/km) and heat flows (>468 mW/m2). There are more than 20 hot spring sites in Jammu and Kashmir State, of which 12 are in the Chenab Valley in the Lesser/Central Himalaya, at least four are in the Kashmir Valley and six are in the High Himalaya region of Ladakh.
The hot springs in Jammu and Kashmir State form part of the Northwest Himalayan Geothermal Province, which extends along the Himalaya mountain belt both to the southeast, into the neighbouring states of Himachal Pradesh and Uttarakhand and on through Nepal and Tibet, and to the northwest into the Punch, Gilgit, Hunza and Yasin valleys in Pakistan-controlled Kashmir and the Northwest Province of Pakistan. All the main hot spring sites are concentrated along major tectonic features formed during the collision of the Indian and Eurasian plates. Geothermal resources within the Himalayan Geothermal Province have already been developed in Tibet. A binary 5 kW pilot geothermal power plant was also commissioned at Manikaran in the Kulu District of Himachal Pradesh in the 1990s.
The power requirement in Ladakh today is around 100 MW and is increasing annually. Present total civil generation is about 13.5*nbsp;MW. Domestic diesel generation (including hotels) may be another 3 – 5 MW. In addition, the army generates around 15 MW. Two hydro projects, at Chutak and Nimoo-Bazgo of 46 MW each are planned. Vvariability of hydro power output during winter means that some diesel power generation may be required as back-up.
It is estimated that geothermal resources at Puga could generate 20 MW with additional generation from Chumathang and Panamik. Geothermal is viewed as the only option for power generation for the Leh district if the use of diesel is to be avoided. This would improve the lives of local people and army and paramilitary personnel posted to the area. A demonstration plant producing between 2 &hndash; 5MW has been proposed to prove the potential.
In collaboration with Cluff Geothermal Ltd we are working on the characterisation and drilling of large (several 100s of MW) hydrothermal systems in major calderas, and on faults crossing them, in Kenya and Ethiopia. Major caldera structures are widespread in this region and natural hydrothermal manifestations are commonly found within them and on their flanks. Initial field reconnaissance strongly suggests that most natural hot springs and fumaroles occur along major faults aligned sub-parallel to the present day axis of maximum (compressive) stress (approximately NNW – SSE).
The initial conceptual model for these hydrothermal circulation systems is that convection above the heat source (still-cooling intrusions of late Quaternary age) is focussed via fault-provided permeability. An open question concerns the relative proportions of young meteoric and deeper-seated magmatic waters entrained in these convection cells. The relatively high rainfall on the elevated flanks of the Rift ensures there is no shortage of meteoric recharge in the area; at the same time petrographic evidence suggests that many of the eruptive products had significant volatile contents, so that ongoing de-gassing of cooling plutons could well be resulting in significant steam transfers to deep circulation systems.
By application of noble gas isotopic techniques, petrographic work on cuttings from Cluff Geothermal's drilling activities, integration within a structural geological framework and application of the latest geothermal reservoir modelling algorithms (building on recent work at Las Tres Virgenes in Mexico, see below) we aim to develop a robust conceptual hydrogeothermal model for these important energy resources, allowing objective evaluation of their long-term reliability and guiding decision-making in reservoir engineering.
Three dimensional modelling of the emplacement and cooling of two Quaternary plutons in this volcanic system associated with the southern extension of the world-famous San Andreas Fault system in southern Baja California, Mexico, has yielded a robust assessment of the current (10 MWe) and potential future geothermal power yield.
The study involved development of new reservoir modelling code that takes into account geologically recent subsurface and topographic changes, as extra lines of evidence in constraining reservoir geometries and hydraulics. (See: Verma, S.P., and Guerrero-Martínez, F.J., 2013, Three dimensional temperature simulation from cooling of two magma chambers in the Las Tres Vírgenes geothermal field, Baja California Sur, Mexico. Energy, 52: 110–118).
A hydrogeothermal walkover survey on the western flanks of the actively-erupting Soufrière Hills Volcano identified ongoing discharge of neutral chloride waters, with chemical signatures (notably in B content) redolent of active interaction with superheated steam at depth. An area for further investigation was identified in a location relatively sheltered from further volcanic hazards. (See: Younger, P.L., 2010 Reconnaissance assessment of the prospects for development of high-enthalpy geothermal energy resources, Montserrat. Quarterly Journal of Engineering Geology and Hydrogeology 43: 11 – 22).
On this basis the UK government's Department for International Development commissioned an MT survey in the indicated location (undertaken by EGS Inc. of California), which produced signatures consistent with the presence of an active hydrothermal circulation system at depth, probably fault-controlled. The first of several deep boreholes above this structure has recently been completed by Iceland Drilling, thoroughly vindicating the predictions of our original conceptual model.