Abstract

Gravity-Magnetic exploration was first carried out in Cambay Basin in 1956-58 and the first 2D seismic survey in this basin was done in 1957-58. Since 1957 till date, ONGC has made large strides from single fold to multifold, from 24 to 4000 recording channels in 2D, 3D, 4D, and 3D-3C seismic data acquisition. Understanding of near surface is an important aspect for getting good quality seismic data, which results in better sub-surface imaging. Weathering and sub-weathering layer thicknesses, velocities and lithology play a vital role in determining good shooting media to get good quality seismic data. Seismic crews conduct close grid uphole surveys combined with pulse data for fine tuning to understand the near surface parameters and in selecting the proper shooting medium