Imaging the Varied Lithology by Using Converted Shear Waves – a Case Study

Abstract

 Seismic velocities have long been used to determine the structural and stratigraphy traps suitable for the accumulation of hydrocarbon. In the present study an attempt has been made to differentiate between such subsurface rocks, bearing significant potential of hydrocarbon, using shear wave velocities. Six seismic lines and Gujwaro well, located in the Lower Indus Basin, have been used to investigate the Lower Goru Formation, which make its presence within time interval of 2000 to 2400 msec.
Seismic parameters such as poisson’s ratio (б), primary and secondary wave velocity (Vp/Vs) ratio, and reflectivities are used to determine the reservoir characteristics. Rock model is prepared for the study area on the basis of these properties, which indicate the existence of soft, intermediate and hard rocks. As the Poisson’s ratio being a function of Vp and Vs is relatively low in shales and high in calcareous sand where as its values varies from 0.23 to 0.25 for Gas sands. Similarly for gas sand the value of Vp/Vs falls in the range 1.68 to 1.74. From the findings of the study it is inferred that gasproducing zones lie in the intermediate rocks. The interpreted subsurface lithologies consist of pure sands, gas sands, shales and calcareous sands