The Seismic Progress Ladder — Where Are You On It?

Ian Jack
Consultant, Sandy, United Kingdom

Nobody would dispute the value of 3D seismic data. Equally, nobody would agree that current 3D seismic images possess the resolution and signal-to-noise ratios that we need to establish the reservoir architecture and its characterisation to a satisfactory degree.

But the seismic method continues to progress. Time-lapse (4D) seismic data routinely demonstrate the ability to resolve ambiguities and uncertainties in architecture and reservoir quality, in addition to seeing fluid movements and sometimes pressure changes.

The value of full-azimuth seismic data, intuitively obvious, is now being demonstrated thanks to the higher oil price and to some increased initiative and risk-taking (in a normally risk-averse industry). New anagrams such as MAZ and WAZ have appeared referring to multi- and wide-azimuth data, some examples of which will be shown and are impressive.

The current focus is on how to acquire these data sets cost-effectively, and one way is to move to the sea-floor with ocean-bottom cables. Historically, OBC data have been five times the unit cost of towed-cable data, but equipment and techniques have improved, and meanwhile the cost of towed cable data has at least doubled. An additional attraction of ocean-bottom methods is the physics which is so much better that it could justifiably be called irresistible. The result is better resolution, sharper seismic pictures, the ability to see properly under platforms, and, occasionally, the additional benefits of shear-wave data. Again, examples of these will be shown.

At the top of the ladder we have emplaced sea-bed detector systems which have all the above advantages and which additionally allow cheap and frequent "on demand" seismic data to be obtained. These allow movies to be made of fluid and geomechanical changes, and provide detailed insights into reservoir depletion mechanisms.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery