Analytical Velocity Modeling in High Pore-Pressure Environment, Offshore East Coast of India

A reliable time-to-depth conversion becomes quite challenging in a complex high pore-pressure depositional environment. This study examines various relations between depth and interval velocity to ascertain plausible models to be used for conversion from time to depth when processing surface seismic data. Sonic data from two wells each from the Mahanadi basin, the Krishna-Godavari basin and the Cauvery-Palar basin in the offshore east coast of India have been used for analysis. Four time-depth models have been tested on selected data set. The first is a linear interval velocity model in depth; the second, the linear interval velocity in time; the third, the average velocity in time and the fourth, the exponential interval velocity in time. The results from time-depth modeling suggest that the average velocity model in time is the most plausible model among all the models analyzed here. This model can be used for time to depth conversion of surface seismic data in the high pore-pressure zones of Mahanadi Basin. This study suggests that the testing of various analytical velocity models is extremely important before utilization of well velocities for the prediction of pore-pressure at any new drilling location.