INTEGRATED STUDY FOR RESERVOIR CHARTERIZATION USING GEOPHYSICAL METHODS FOR MEHAR BLOCK, CENTRAL INDUS BASIN, PAKISTAN

Abstract

Mehar gas field is a recently developed gas field of the Central Indus Basin. The objective of this research was to identify the subsurface structure of the area and to characterize reservoir potential of the Pab Sandstone which is the main producing reservoir for Mehar block. First, for the delineation of the subsurface structure, seismic interpretation was done over the 3D seismic data cube which showed the presence of a large fault-bounded anticline and a north-south trending reverse fault. This research also utilizes the advanced seismic techniques like seismic inversion and seismic attribute analysis along with petrophysical analysis of Mehar-02 well. Seismic inversion helps to determine the acoustic impedance for the main reservoir of the area. Inversion results shows high impedance zone towards west of the area due to compaction of Pab Sandstone, but these impedance values decrease on the east because of the presence of a large reverse fault. Porosity computation is also done over inverted data of Mehar block which shows that the sand of Pab Sandstone are very much compacted and most of the porosity is secondary. Porosity computed by this techniques was almost equal to the results obtained by petrophysical analysis and lies in between the range of 7% to 7.4%. Four different attributes were applied over Pab sandstone including instantenous frequency, instantaneous phase, relative acoustic impedance and trace envelop attribute. .Attribute analysis for Pab Sandstone show very little variation on the west side because of compacted sandstone for all applied attributes but variation for these attributes were seen towards the east near to the fault. Large number of fractures are observed near fault which cause decrease in values for mentioned attributes. Petrophysical analysis of Mehar-02 well showed only two small zones of 1.5-meter near the formation top and a 3-meter zone at the depth of 4011 meters having 6% to 7% porosity and around 60% hydrocarbon saturation.