2D Seismic Interpretation, Petrophysical and Fault Seal Analysis, Volumetric Evaluation of Balkassar Field, Upper Indus Basin, Pakistan (P-1158) (MFN 4880)

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.