Download Tapoban Geothermal Field, Alaknanda Valley, Chamoli, Uttarakhand

Geological Survey of India
Tapoban Geothermal Field, Alaknanda Valley, Chamoli, Uttarakhand
Thermal springs along Alaknanda Valley (Chamoli district, Uttarakhand) is spread over 35
km stretch and the main spring localities are Badrinath 56°C, Ghorshali 25°C, Loani 62°C, Kanakar
58°C, Gulabkoti 49°C, Langsi, Gari 65°C, Bhapkund 31°C, Juma 65°C, Tapoban 65°C, Paiyan
54°C and Kharao 66 °C.
The most promising locations for geothermal investigation were found to be around
Tapoban and Badrinath, which are on the way from Joshimath to Malari and Mana respectively at
15 km and 25 km away from Josimath. The geothermal exploration started in the in the year 1974
with
geological
and
geochemical
mapping,
geophysical
investigation,
thermal
gradient
measurement besides slim hole drilling. The investigation lasted up to the year 1989.
Geology: Regionally the rocks in the area belongs to two tectonic units trending almost E-W and
divisible in Central Crystalline and Garhwal Groups. The Central Crystalline rocks are highly
metamorphosed in compare to Garhwal. The groups are separated by a tectonic plane locally
called Main Central Thrust. The Central Crystalline constitutes the rocks like biotite/augen gneiss
chlorite/mica schist with quartzite and marble, while Garhwal contains slate, phyllite, quartzite,
dolomite with lenses of basics.
Thermal springs have been reported in Central as well as in Garhwal Group of rocks but
the Central Crystalline have thermal springs with higher temperature in compare to Garhwal
Group. The discharge is low to moderate and rarely exceed 500 liter/min in the area. Secondary
deposits around spring have been reported as carbonate and sulphur with weak gas emanation.
Geophysical Survey: 5 shallow drill holes have been drilled in Tapoban area for thermal gradient
measurement in depth range 50m to 52m. In addition to the above 5 holes deep drill holes are in
the range of 100.10m to 728.20m to examine the geothermal condition at depth. The maximum
recorded subsurface temperature in shallow hole is 57°C with sub-artisan condition. While deep
exploratory drill hole shows maximum recorded subsurface temperature around 107°C.
Electrical resistivity sounding using Schlumberger configuration with maximum AB/2 varying
from 150m to 400m have been carried out in area of thermal manifestations. Conductive layer at a
shallow depth has been reported followed by a high resistive zone. At Badrinath lower order
resistivity is in the range of 60 to 250 Ohm-m with thickness ranging from 20 to 250 m. At Tapoban
a shallow conductive layer of the order 90 Ohm m at the depth 20 to 100m has been envisaged.
The low conducting layer has been attributed to fractured rocks of gneiss or quartzite, in which
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Geological Survey of India
thermal fluid may be existing. Resistivity data indicates a shallow thermal zone in the area but the
data are insufficient to prove or disprove any deeper thermal (conductive) zone. The S.P. and
magnetic survey show 30 mv. to -30 mv. and 100 gammas to -100 gammas respectively, however
no significant anomalies were indicated by this method.
Exploratory Drill: 5 thermal gradient drill holes and 5 exploratory holes were carried out, in the
entire Alaknanda valley. Out of these five exploratory holes one is at Badranath and rest are
around Tapoban. At Badrinath the drill depth is about 100m. The hole recorded temperature a
15°C at a depth 38m. Thus the observed thermal gradient was average and secondly because of
sensitivity of the area the geothermal work was shifted to Tapoban. At Tapoban the drill hole depth
varies from 292m to 728m and thermal artisan condition was encountered in all the holes in the
depth range between 79.6m to 515.7m. Artisan condition has been reported mainly in quartzite of
Central Crystalline. During drilling a strong blow out was recorded in one of the hole at 427m depth
with discharge 800 l/m and temperature 90°C (at surface). The pressure in the dill hole was
measured up to 7 kg/cm2.
Geochemistry: Thermal Spring and drill hole discharge were collected and analysed for HCO3,
CO3, Cl, SO4, F, Ca, Mg, K besides pH B, SiO2 and specific conductance and total dissolved solids.
The chemical analysis from thermal springs and drill holes flowing under thermal artisan condition
are shown below.
600
500
400
300
200
100
0
HCO3
mg/l
Cl
mg/l
SO4
mg/l
Ca
mg/l
Mg
mg/l
Na
mg/l
K
mg/l
SiO2
mg/l
TDS
mg/l
The springs and drill holes water are of low TDS, Cl and SiO2 and hardly exceed 570 mg/l,
10 mg/l and 120 mg/l respectively. On the other hand the hot water is high in HCO3.content in the
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Geological Survey of India
TDS. The atomic ratio Cl/HCO3/Cl in thermal water are low for (<1) and Na/K ratio <6 or >18, such
water do not indicates high subsurface temperature. Moreover the the type of thermal water on
Giggenbach diagram Cl-HCO3-SO4 is bicarbonate, such water indicate shallow underground
circulation and do not attain equilibrium with rock water interaction at higher temperatures. The
geo-thermometer, are empirical equation, based on thermodynamics of water chemistry and
indicates subsurface temperature. Different empirical Geothermometers have been used in the
area for evaluating subsurface temperature and Quartz, Chalcedony and K-Mg geothermometer
are in agreement to each other. Evaluated sub-surface/reservoir temperature comes out around
100+10°C at the subsurface.
Different empirical Geothermometers used in the area for evaluating subsurface
temperature area given below.
Geothermometer
Concentrations
Quartz = [1309/(5.19-log S)]-273.15
S= SiO2 in mg/l
Fournier (1977)
Chalcedony=[1032/(4.69-log S)]-273.15
S= SiO2 in mg/l
Fournier (1977)
K-Mg =[ 4410/(14.0-log K2/ Mg)]-273.15
K and Mg in mg/l
Giggenbach (1988)
The thermal fluid of the area is of low enthalpy and economically can be utilized for direct
applications, such as spa, greenhouse farming, space heating and for tourist attraction.
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Geological Survey of India
Thermal Spring at Tapoban, Chamoli, Uttarakhand
Thermal water under artesian condition from Drill Hole at Tapoban
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Geological Survey of India
Drilling Activity at Tapoban Geothermal Field
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