AN ASSESSMENT OF THE GEOTHERMAL ... - Orkustofnun

Report 5 15 Akbar
4.2 Northwest stable shelf part of Bangladesh
The northwest stable shelf area is
characterized by limited to
moderate thickness of sediments
above the Precambrian igneous
and metamorphic basements
(Figure 10). This unit is
geologically stable in relative
terms and has not been affected by
post collision fold movement.
Interpretation of an aeromagnetic
map of Bangladesh revealed the
existence of a number of welldefined
faults in the stable
platform (Hunting Geology and
Geophysics Ltd., England, 1980).
These faults are thought to be
basement controlled with an
associated fracture system
development mechanism for
transferring heat to the overlying
rocks. Some of these faults,
bounded by intracratonic grabens,
contain Gondwana coal. The area
has a minimum sedimentary
thickness of as little as 130 m
(Figure 11). Temperature data
from the deep hydrocarbon
exploratory wells as well as many
shallow wells helped to identify four
prominent zones including three very
high thermal anomalous zones in the
Stable zone; these zones are
discussed below.
FIGURE 10: Geotectonic map of northwest Bangladesh
(after Guha et al., 2010)
Bogra shelf
The Bogra shelf (Bogra slope)
represents the southern slope of the
Rangpur Saddle which is a regional
monocline plunging gently to the
southeast to the Hinge zone (see
Figure 1). This zone marks the
transition between the Rangpur
saddle and the Bengal Foredeep from
a depositional as well as a structural
point of view. The width of the
Bogra shelf varies from 60 to 125 km
up to the Hinge zone and the
thickness of the sedimentary
sequence increases to the southeast.
FIGURE 11: Generalised NW-SE across the crystalline
basement rise of the Rangpur saddle (Guha, 2010)
Four deep wells have been drilled in the Bogra slope, namely the Singra 1, Bogra 1 and 2 and Kuchma
1 with the highest drilling depth of 4100 m at Singra 1 in the northwest region. The Singra-Kuchma-