Quantification of 4D signal and generating density change maps: An East Coast Canada case study

This abstract describes how an East Coast Canada 4D data set was calibrated for quantitative analysis.We found a linear relationship between 4D amplitude change seen in the 4D seismic at well locations, to the modeled acoustic impedance change from the rock physics relationships to known saturation and pressure changes. From this linear relationship we converted the 4D amplitude change cube into a % impedance change cube. The range of the scatter to the best fit line is the seismic-to-model uncertainty +/- 1%: the noise floor.Through our rock physics relationships, the seismic-to-model noise floor is translated into something more practical. Defining expectations of what the 4D can and cannot see in terms of pressure or saturation change.By differentiating the acoustic impedance equation, we show how a density change map was made by subtracting a velocity change map from its equivalent impedance change map. The 4D velocity change cube is generated from the time alignment process of base line to monitor.A density change map is not subject to the impact of pressure changes of a standard 4D amplitude change analysis. It directly shows sweep in the reservoir. Shortcomings of the density map generation is the low resolution (~60m) of the velocity change seismic cube.