Abstract:
The Balkassar field is located in southern Potwar Basin which is a sub basin of Upper Indus Basin,
Pakistan. Tectonically, the study area lies in a compressional regime where reverse faults are observed
which make pop up structures. To reduce the risk and problems during drilling a well, the evaluation of
reservoir properties is very important 3D seismic cube were interpreted by correlating with well data of
Balkassar OXY-01. It appears probable the early Eocene age Chorgali Formation could offer commercial
production with lower water cuts from the eastern lobe (yet untapped) of the structure that may have at
least 30 million barrels of unrecovered oil. Four horizons in 3D seismic data were marked and pointed
out. Two prominent faults were identified and interpreted on the seismic sections. The contours of the
horizons (Chorgali, Sakesar and Patala and Khewra formations) are trending north-east to south-west. The
contours in the region of the faults illustrate reverse faults forming pop-up structure i.e. north-west and
south-east dips and north-east and south-west strike. 3D depth surface models were generated which
indicates that the major structure has lower pull out in the course of north-east to south-west with sinking
along south-east and north-west directions.
The Chorgali Formation (2425m-2490m) were marked and encountered lithologies are composed of
limestone and dolomite. The values of GR-log (Gamma Ray Log) shows high values which indicate that
the Patala Formation (2605m-2625m) is mostly consist of shale. The Khewra Formation (3050m-3125m)
values were relatively ~50% sandstone, ~10% sandy limestone while rest of the formation is shale (high
GR-Log values). The targeted reservoirs in Balkassar oil field are Chorgali and Sakesar Formations in
well BLK-OXY-01. The overall depth range of the reservoirs zone were marked is in between 2420m to
3100. The reservoir area has a seismic reversal, where the low impedance area indicates the presence of
limestone opposite the shale. Now, using an impedance graph model from the well data, an initial map is
developed in the time interval between 1300 ms and 1450 ms in which interest is generated.
The seismic interpretation and modeling alongside the petrophysical analysis were then quality
checked via qualitative rock physics analysis. From the Kdry/Porosity plot, the limestones were
generally observed to lie within the 2420-2580m which indicates a high level of compaction.
From high impedance values can be observed on a seismic cube of 2600 m, and these values
decrease slightly as you go up. This shows that we have Patala shale at 2,600m and as we go up
we are approaching the reservoir area at 2,400-2,580m.
