Tectono-Stratigraphic Model for Ghazij Formation and its Implication on Hydrocarbon Exploration in Kirthar Foldbelt, Pakistan

Ahmad, Abrar; Ali, Moshin; Hussain, Abid; Sardar, Naeem
Exploration, Pakistan Petroleum Ltd, Karachi, Pakistan.

An abrupt change in lithology and thickness of Ghazij Formation of Late Paleocene - Early Eocene and its isochronological units, from east to west within short distance along depositional strike, has been observed in Kirthar Foldbelt, Lower Indus Basin Pakistan. These changes are attributed to shelf break controlled by Kirthar Basement Fault (KBF) that was active during the deposition of Ghazij Formation. Surface and subsurface data provides an excellent opportunity for understanding the influence of this tectonics event on sedimentation and paleogeography at this rock unit. Gross lithofacies distribution maps also advocate the deposition of Ghazij Formation in tectonically active basin.

In the present study seismic, stratigraphic transects and gross depositional environment (GDE) mapping used to explain the lithofacies variation of Ghazij Formation in the area.

Kirthar Basement Fault is considered a normal fault created by the breakdown of Gondwana and reactivated during Late Paleocene - Early Eocene time due to collision of North Western Indian Plate with Kabul block. KBF is possibly present between the Tangna Pusht Nala section and Tangna Pusht - X1 well and played a critical role in controlling the physiography of the basin and consequently on the thickness and lithofacies of Ghazij Formation. across the basin. Similar variations are also observed across depositional strike along three other sections and on seismic lines. Ghazij Formation has its time equivalent lithofacies of dominantly limestone to the east of KBF, where carbonate production was able to keep pace with the rate of sea level rise with limited clastic supply whereas thick basinal shales were deposited to the west of KBF. The presence of Marap Conglomerates and marginal marine facies in the upper part of Ghazij Formation, towards the western side of KBF, suggest some uplifted areas within basinal settings.

Common Risk Segment (CRS) map of Ghazij Formation as a seal based on regional lithofacies model help in explaining the possibilities of failure and working of Dunghan Play in the Kirthar Foldbelt. The absence/thinning and presence of effective regional seal over Dunghan carbonates decrease the prospectivity in the eastern and increase in the western part of Kirthar Foldbelt respectively.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012