Introduction

Seismic reservoir monitoring aims to use multiple 3D seismic surveys acquired at different calendar times to directly image fluid movements, pressure/temperature fronts or other effects of production in the subsurface (e.g. Lumley, 1995). Unfortunately, different generations of 3D seismic can exhibit seismic differences unrelated to reservoir production, caused by different (or non-repeatable) seismic acquisition and processing artifacts. The aim of cross-equalization is to remove processing and acquisition differences between time-lapse seismic surveys, so comparison between them can be interpreted in terms of genuine fluid-related changes.

Since reservoir monitoring is a relatively new technology and individual case studies tend to vary significantly, the industry has not developed a standard 4-D processing flow. However, cross-equalization of post-stack seismic datasets typically includes the following generic elements:

1.

Survey realignment to a common grid, including spatial and temporal re-registration to correct the effects of geometry errors, differential statics, or different velocity functions used for NMO and migration.

2.

Bandwidth and phase equalization to compensate for different source wavelets, for example.

3.

Amplitude balancing to scale the data to the same amplitude (or energy) level.

3-D seismic surveys are often repeated for purposes other than reservoir monitoring (improvements in acquisition technology, imaging different targets etc.). In these cases, additional processes may need to be considered to balance spatial frequency or dip-content, for example.