explorationstrategy indus basin (Inner Folded Zones)

Inner Folded Zones (Tectonic Feature C,):According to Raza et al. (1989), the western flanks of
the Sulaiman and Kirthar depressions are bounded by uplifted and folded zones comprising
Zindapir, Mari-Bugti, Sanni and Mazarani zones. Parachinar-Kala Chitta fault-fold zone bounding
Kohat-Potwar depression in the north is for the time being excluded because of our poor knowledge
of the subsurface picture beneath this complex zone. These zones also represent deformation. Here
the uplift has brought prospective reservoirs higher in trap conditions, thus enhancing oil and gas prospects.Theanticlines are in the form of box-like folded zones forming pronounced ridges passing
into wide synclincs. There is large numberof gas fields in these zones. At least four petroleum zones
can be delineated,and areasfollows:
Zindapir Folded Zone (Petroleum Zone C,): This zone is a north-south elongated narrow region
flanking the Sulaiman depression in the east and is comprised of the Zindapir, Afiband, Rodho,
Dhodak and Domanda anticlines all of which have steep eastern limbs and gentle western flanks.
This chain of ridge-forming anticlines turns westwards in the south and seems to merge with the
Mari-Bugti folded zone. Condensate from Dhodak and gas from Rodho structures have been
discovered in Cretaceoussandstone reservoir.
Mari-Bugti Folded Zone (Petroleum Zone C2): The Mari-Bugti area comprises three chains of
anticlines with intervening synclines. The folds are sub-latitude arranged and increase in amplitude
and deformation northwards. The chains are: (1) Sui-Uch, (2) Giandari-Loti-Zin and (3)ShamkalikPirkoh-Bambor. Neogene molasses cover the Sui-Uch sub zone, whereas various horizons of
Paleogene form the central parts of the Giandari-Loti-Zin and Shamkalik-Pirkoh-Bambor sub¬ zones. The area is mainly gas prone and contains many gas fields including the giant Sui field, but
some oil shows are present in its northwestern edge. The Cretaceous and Eocene plays need to be
furtherevaluated.
Sanni Folded Zone (Petroleum Zones C3): The Sanni is a narrow folded zone flanking the Kirthar
depression in the east. The zone islongitudinally orientedand comprises Sanni and Bannh anticlinal
sub-zones, which expose marine Eocene and continental Oligocene sediments in the central parts of
theanticlines. Thezone isdown warpingnortheastwards. Oil seepages are present in thezone.
Mazarani Folded Zone (Petroleum Zone C4): The Mazarani zone is the southern extension of zone
C3 west of the Kirthar depression. Like Sanni Zone (C3), it also has a longitudinal orientation. The
zone comprises a northern anticlinal uplift (Mazarani anticline, which contains gas condensate in
Lower Eocene carbonates) and a southern up dipsloping towards the Kirthar depression. Eocene and
Cretaceous play meritinvestigation.
Outer Folded Zones (Tectonic Feature- D):The depressions are succeeded in the north and west by a
mountain belt comprising Parachinar-Kala-Chitta, Sulaiman and Kirthar ranges. These ranges were
produced during the Tertiary by collision and coalescence of the Indian and Eurasian plates. Here
only Sulaiman and Kirthar ranges are discussed because the Parachinar-Kala Chitta ranges,
according to our present level of information, hold some hydrocarbon potential in the sub thrust
zones,where trapdelineation can only be done throughintensiveseismic survey.
Sulaiman and Kirthar Ranges (Petroleum zones D, and D2): As discussed earlier, these zones
represent the deformed and uplifted areas of the Indus basin because of their position near the
collision front.
The Sulaiman range swings from northsouth to eastwest formingan arcuate chain. Western
part of the chain is formed of Fort Sandeman-Loralai sub zone. Older rocks (mainly Mesozoic) areexposed in sharp folds often complicated by faults. The part close to Zindapir and Mari-Bugti folded zones contains some interesting anticlinal folds, which can be considered as potential exploration   targets. A gas field (Jandran) in the Cretaceous reservoir and a number of oil seepages in the eastern part of the zone prompt'investigation and evaluation of the Cretaceous. The Kirthar Range is a north-south oriented tectonic feature. The inner or western Fort Sandeman-Loralai sub zones extend southward into Kirthar Range and are represented by Quetta and Mor sub zones. The eastern or outer part of the Kirthar Range containing Bolan and Gaj anticlinal sub zones having Mesozoic-Neogene sediments. This part may have potential for hydrocarbon in Jurassic and Paleogene plays as indicated by the occurrence of oil seepages at Hernia, Bambina, and Gourd. r Rear Depression (Tectonic Feature - E): It occurs in between the Chaman Fault and the obducted ophiolitic margin of the Indianplate.The boundary of there depression follows the patterns of Sulaiman and Kirthar ranges, although sediments infill and tectonics are not identical. Turbiditic sequence from Oligocene Miocene pile up in the basin with sporadic exposuresof Eocene carbonates. Tight anticlines, broad synclines and northwardly dipping thrusts are characteristic features. Dark shales associated with turbidites are considered as potential source rock. There is no dearth of structures with large closures.Pishin Depression (Petroleum Zone- E): This depression is filled with fine elastics of Cenozoic age underlain by Eocene carbonates. The sediments have been strongly deformed, sheared, folded,faulted and refolded. The synclines have occupied high relief position and anticlines have slipped in depression. The complicated structural geology demands careful evaluation of the zone. Ahmed et al.(1991)stated that the thickness and lithology of the sedimentary fill and reporting of seepage indicate some potential for the occurrence of hydrocarbon in the basin. However, considering the tectonic setting and sedimentary pattern, it is more gas prone than oil.