Introduction

Seismic reservoir monitoring is a new technology that uses multiple 3D seismic surveys to directly image fluid movements, pressure/temperature fronts or other effects of production in the subsurface Lumley (1995). Unfortunately, different generations of 3D seismic can have many small differences due to the complexity and non-repeatability of seismic acquisition and processing. The aim of cross-equalization is to remove processing and acquisition differences between surveys, so comparison between them can be interpreted in terms of genuine fluid-related changes.

Cross-equalization of post-stack seismic datasets, typically includes the following elements:

1.

Survey realignment to a common grid.

2.

Amplitude balancing to scale the data to the same level.

3.

Bandwidth equalization due to different source wavelets.

4.

Phase matching to correct residual phase differences.

5.

Spatial and temporal re-registration due to geometry errors, different static solutions or velocities used for NMO or migration.

In a previous SEP report, Rickett (1997) discussed the use of L2 match-filtering to simultaneously correct bandwidth, phase and static shifts between surveys. Unfortunately, the amplitudes of the L2 filters are biased by the presence of uncorrelated differences between the surveys, and the amplitude of coherent events is not be equalized correctly.

Similarly, any scheme that is based on equalizing the energy in the two surveys, implicitly assumes that their random noise levels are equal, which may or may not be the case.

We present an approach that scales the amplitudes based on the relative signal-to-noise levels, and test the approach on a synthetic example that has many features observed on 4D field datasets.