Abstract:
Balkassar Oil Field discovered in 1945 by the Attock oil company of Pakistan,
it is one of the oldest known Oil Fields of Pakistan. It lies in the Central Potwar on the
southern flank of Soan Syncline. This seismic survey was carried out in 1981 to
discover the potential of the sedimentary sequences ofChorgali Formation of Eocene
age and Khewra Sandstoneof Early Cambrian age. The surface geological information
does not reflect the subsurface geometry of the Balkassar Anticline.
The already interpreted 2-D seismic data, consisting of seismic lines PBJ-02,
PBJ-03, PBJ-04, PBJ-05 and PBJ-10 is re-interpreted. The major aim of interpretation
is to reveal as clearly as possible the subsurface structure of the Balkassar Anticline
and to deduce the possibility of hydrocarbon occurrence in deeper horizons of the
sedimentary sequence. The well data of Balkassar Oxy # 1 was used to confirm the
reflectors depth. The interpretation includes the construction of time and depth
contour maps of Chorgali, Sakesar, Lockhart, Tobra and Khewra horizons. Time
contour maps of the reflectors were produced using two way time of the reflectors.
Velocity analysis was done to find out velocity values at every shot point, these
velocities were used to find the depths of the formations for the seismic
section.Petrophysical analysis helped to find out the zone of interest within the
formations and volumetric evaluation gave the information about the estimated
reserve in the formations. The interpretation of Geo-seismic section showed that the
area was structurally deformed due to salt decollement and compressional tectonic
movements. The Balkassar Structure is a long, northeast southwest trending double
plunging anticline. The structure is bounded by tear and reverse faults. The
northwestern flank of the structure is steeply dipping and is terminated by southeast
dipping reverse fault. Estimated horizontal closure of Balkassar Anticline is 80 sq.km
and the vertical closure is 365 meter. Two decollment surfaces are present, one in the
Pre-Cambrian Salt, the other in Neogene Sediments. The compressional tectonic of
the structure is obvious from the reverse faults that bound the plunge of the structure.
The Geoseismic section of PBJ-04 shows a salt-cored Pop-Up structure, which is one
of the most favorable structures for oil and gas accumulation. Allen diagram was
made to do the fault seal analysis with in the subsurface.
