Lithology substitution in fluvial sand

Dichotomy in geophysical remote sensing is both relative and absolute: while the seismic reflection relates to the impedance contrast, the reservoir properties, such as porosity, relate to the absolute value of the impedance. One way of interpreting the relative in terms of the absolute is to perturb the absolute and calculate the corresponding relative. To accomplish this task in geophysics, the velocity and density curves from an existing prototype well are perturbed according to a likely situation at a different location. A new pseudowell thus created is used to generate synthetic full-waveform seismograms which are then compared to real data at the location, with the expectation that the similarity in the seismic response reflects the similarity in the reservoir properties.