Improving Recovery and Insight by Improving 4-D Seismic Resolution

Rodney Calvert and Andrey Bakulin
Shell Intl. E and P Inc, Houston, TX

The benefits of field monitoring and seeing what is changing in a producing reservoir has been well demonstrated by several examples using repeated 3D surveys. This however is just a beginning to 4D monitoring and reservoir management. By using new higher resolution approaches we can measure smaller reservoir changes that enable diagnosis over a smaller time interval and thus earlier results. Improved sensitivity gives an improved ability to distinguish between saturation, pressure, compaction and temperature changes associated with production.

Sensitive monitoring depends upon an ability to exactly repeat measurements to determine small accurate differences. By using a new Virtual Source approach to imaging with permanent buried or sea bottom receivers we can exactly repeat the geometry and waveform of seismic measurements even when the sea state, or near surface and physical sources change. This results in better, faster and cheaper repeat surveys and enables a capability for better resolving small changes, better resolving thin beds and locating changes within a reservoir and better resolving the rates of change by more frequent and affordable surveys.

The Virtual Source approach uses rather conventional acquisition but uses computer processing to simulate a point source at each of the fixed receivers. This simulated source may be designed to correct for near surface time shifts and transmission distortion to radiate downwards with a known designed waveform using all the bandwidth available without any knowledge of the overburden or the source waveforms or their exact positioning.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005