2-D Seismic Interpretation of Line PBJ-10 & Analysis of Shear Wave Velocity Estimation Techniques Along with Reservoir Zone Identification Using Well Log Attributes.

Abstract

Seismic line PBJ-10 was given by the department of Earth Sciences, QAU Islamabad for interpretation which comprises of 102 vibrating pOints from COP 99-200. To investigate the lateral and vertical variations of velocity, average velocity and Iso-velocity maps were generated. Total seven reflectors and one thrust fau lt are marked. Reflectors were given names by using the data of OXY-1 well. To see reflector position time and depth sections were prepared. Time and depth contour maps of Chorgali Formation were generated by using the 'SURFER' software. These show anticlinal structure of the Chorgali Formation in the Balkassar area, so this may act as trap for hydrocarbons. Different shear wave velocity estimation techniques were compared and it was found that Krief's Relation is better among the Krief's Relation and Normal Castagna's Equation but when the Normal Castagna's Equation is compensated for volume of shale it gives best results, it was also confirmed by generating synthetic seismograms. Corrected Castagna's synthetics give best results as they give good amplitude and no significant noise. These results were used for the calculation of Vs used in the rock physics parameters.Joyamair-4 was used for this purpose. Corrected shear wave velocities produced the best results and the reservoir zone was marked from 2046-2054m in the Chorgali Formation. As volume of shale is less in this zone, porosity is high, density is less, P and S-Wave impedance have less value, VpNs have value in the range 1.8-2, Poisson's ratio and Poisson's Impedance have high value in the reservoir portion. All these results are confirmed by the Poisson's Damping Factor whose value also lies in the range for limestone reservoir. So all these attributes confirm the presence of hydrocarbons bearing zone in the Chorgali Formation. It is also confirmed by the cross plot of GR vs PDF which separates hydrocarbons bearing carbonates from shale and carbonates.