BACKGROUND RESISTIVITY ESTIMATION FROM SEISMIC VELOCITIES

Abstract

Interpretation of Electromagnetic data requires solving a forward problem wherein a model of earth is required with assumed values of electrical resistivity. This earth model is invariably a layered earth model. The resistivity values that must be assigned to the different layers of the layered earth model can be obtained from seismic velocity data obtained from seismic reflection surveys carried out in the area. Although there is not much that is common among seismic and electromagnetic prospecting except that both make use of waves, attempts have been made to extract resistivity from seismic wave velocities. In this connection work done by Faust (1953) is important who developed an empirical relation between P-wave velocity and electrical resistivity. There are many different rock-physics models to relate velocity to porosity and porosity to resistivity. Some are based on theoretical assumptions, whereas others are derived empirically. It is proposed to study these relationships and derive a suitable resistivity-velocity transform, i.e., a relation that gives resistivity from knowledge of P-wave velocity in a porous medium saturated with a given fluid.