RESERVOIR EVALUATION THROUGH COMPARATIVE INVERSION TECHNIQUES, GAMBAT BLOCK, LOWER INDUS BASIN, PAKISTAN

Abstract

Geologically Tajjal Gas Field (Gambat Block) lies in Lower Indus Basin -a proven Geological Province in the Islamic Republic of Pakistan. The field was discovered by OMV Pakistan and is one of the productive fields. The dominant structural styles in Lower Indus basin is normal faulting due to its extensional tectonic regime. The stratigraphic sequence is composed of Jurassic to most recent age rock formation. Based on the synthetic seismogram two horizons Top Lower Goru and B-interval are marked. Time and depth maps define the dip of the area. Faults marked at the reservoir level B-interval has less dip as compared to fault marked on the Top lower Goru. Structural interpretation carried out, is confirmed through post stack seismic attributes. Reservoir properties are estimated through Petrophysical analysis using borehole log data. B-interval sands are clean and show good porosity at the well location. Petrophysical properties namely Porosity and volume of shale are also computed at the seismic level, through post stack seismic inversion using Model based inversion and Band limited inversion. The aim of post stack inversion is to evaluate the sands of B-interval in terms of its porosity and volume of shale distribution. An inversion result proves that there is presence of Shaly sands and porosity also tends to decrease in the south east direction. The average porosity value evaluated with model based inversion and band limited inversion is 8% and 7%.