Explorationstrategy 1 indus basin (The belt of depressions)

The belt of depressions comprises six petroleum zones, they are: Potwar (B,), Kohat (BJ, Sulaiman(Bj), Sibi(B„), Kirthar(B5) andKarachi(B6)depressions.
Kohat-Potwar Province
termed here Petroleum Zone B, and B2 comprises the two depressions. Potwar and Kohat respectively. The province is bounded in the north by Parachinar-Kala Chitta fold belt through a system of faults. The Salt Range thrust marks its southern limit. South-westward, it is separated from the Sulaiman depression by the Pezu uplift. Its western and eastern limits are marked by the Kurram and Jehhim faultsrespectively. The main sediments supply during Tertiary appears to be derived from the rising Himalayas with uplift ending during the Late Pleistocene. However, in past, especially in Eocene the source of sediments was also from the west (see paleogeography  section).
Potwar Depression: The zone B, is'a major oil producing province of the country with production from Jurassic, Paleocene and Eocene rocks. Some discoveries have also been made in Cambrian and Permian. Whereas Kohat depression, the zone B2, still remains an under explored area and holds good prospects for oil and gas. Recent discoveries in this area confirm the occurrence of hydrocarbons. Palaeozoic, Mesozoic and Tertiary hydrocarbon plays merit investigation and estimation in both the depressions.
Sulaiman Depression: This depression corresponds to Petroleum Zone B3 of Raza et al. (1989).
This is a large down warp and is contemporary with the Potwar-Kohat depression. The sediment fill
is of Palaeozoic, Mesozoic and Cenozoic age and covered by Quaternary alluvium and Neogene
molasses. Decrease in the thickness of various rock units towards east is noted from subsurface data.
Simple structure like antiform with pinch-outs and unconformities in the eastern side, offer good
prospects for petroleum
Sibi Depression: Forms Petroleum Zone B4: The Sibi Depression is a narrow, triangular depression
sandwiched between the Sulaiman and Kirthar ranges. Continental molasses with huge thickness
serves as cover on the Paleogene rocks. According to Raza et al. (1989), the fold on the flanks have
some prospects in Eocene carbonates and Cretaceouss ands.Ahmed et al. (1992) made detailed study
of Sibi Forland basin, then presented few concepts and hypothesises based on structural
interpretation, surface geological expression and world analog. According to them two regimes are
present. They are: (1) Wrench associated and (2) up thrust fault bounded regimes. The structural
traps within these together with source and reservoir rocks indicate good prospects for oil and gas.
They added that these types of structural traps have often produced oil and gas in several sedimentary
basins of the world.
Kirthar Depression conforms to Petroleum Zone B3: This zone is a north-south trending down warp
south of Sibi Depression. Its western limit is marked by Sanni and Mazarani folded zones. It has
faulted eastern boundary with the Sindh Monocline. The molasse here is quite thick as in other
depressions. Apparently, the area seems nearly flat, but the possibility of some structural traps
developed due to basement flexures can not be ruled out. There are various possibilities of
development of stratigraphic traps in Paleogene sediments.
Karachi Depression named as Petroleum Zone B6: The Karachi depression is an embayment
opening up into Arabian Sea. The northern part of the depression is raised while the southern part is
submerged under the sea. Mesozoic rocks overlain by thick marine sediments of Paleogene and
Neogene are present. Few gas fields have been encountered in Paleogene carbonate reservoirs and
prospects of oil and gas in other rocks are there, in other words Cretaceous and Tertiary plays need to
be investigated.