STRUCTURAL DEVELOPMENT, STYLES AND HYDROCARBON POTENTIAL OF THE KARACHI ARC
Muhammad Imran and Khan Arshad
Eni Pakistan Limited, Karachi
Karachi Arc is located in the South-Eastern part of the Kirthar Fold Belt. It is an arcuate structural feature, verging towards eastward in a Thin Skin fashion. Sedimentary rocks ranges from Palaeocene to Recent age are exposed in the area. Counter clockwise movement of the Khuzdar Block in the Kirthar Fold Belt during late Oligo/ Miocene time, after the Collision of the Indian plate with the Eurasian (Afghan Block) has resulted in the opening of the Porali Trough in the South Western part and development of the Karachi Arc in the South Eastern part. Two main detachment horizons, the older one lies in early Cretaceous Semabr formation, while the younger one lies in Eocene age Ghazij formation has identified in the area. Presence of detachments and thin skin movement in the Karachi Arc is also supported by the presence of A-Symmetric nature of Anticlines together with flate ramp geometries and Fault Induced folding. Movement of the Karachi Arc in a thin skinned fashion has resulted in the development of number of strike slip faults in the area, acting as lateral ramps, which fascinating the thin skin movement of the cover sequence on the frontal ramps. Main Structural style of the area is proposed as a thin skinned, however some thick skinned deformation has also been reported in the area.
Satellite image interpretation of the Karachi Arc indicates NNW-SSE trends of the anticlinal axis in the northern part, Nearly N-S in central part and NNE-SSW in southern part. This change in the anticlinal trends from north to south in the Karachi Arc has been proposed by the presence of major strike slip faults movements in the northern and southern parts of the Arc.
Karachi Arc exhibit a good hydrocarbon plays potential ranges from Cretaceous to Palaeocene age; some has been already proven by the hydrocarbon discoveries in the area. However a number of structures are still undiscovered and contains a hydrocarbon potential of several TCF of gas in place, which needs to be explored in the context of regional structure and tectonics of the area. Geo-Chemical data on the main source rock including Semabr formation indicates that most of the area is within the gas generation window at the present day condition.
The south-eastern part of the Karachi Arc has a good exposure of the different members of Nari (Oligocene-age) and Gaj (Miocene-age) formations. These formations contains a good reservoir potential within the sandstone and reefal carbonates members, and it can be used as an analogue for the Indus off-shore exploration, where these are the main objectives.
This paper will helps in understanding the structural development, structural styles and remaining hydrocarbon potential of the Karachi Arc in detail, together with regional structure and tectonics, and also as an analogue for Indus off-shore exploration (i.e. South-Eastern part of the Karachi Arc area).
AAPG Search and Discovery Article #90160©2012 PAPG/SPE Annual Technical Conference, 3-5 December 2012, Islamabad, Pakistan.