Inversion of Thin-Bedded Multi-Lithology Settings: What are the Critical Requirements for a Successful Seismic Inversion?

Seismic inversion of thin-bedded multi-lithology stratigraphic systems suffers from problems of nonuniqueness despite significant advances in acquisition and data processing. The Cambo Discovery (West of Shetlands, UKCS) provides a good case study comprising stacked sub-seismic sand reservoirs interbedded with thin coals and shales. Appraisal wells drilled on 1990’s vintage conventional streamer data have proved areas of thicker (but still sub-seismic) sand bodies away from the crestal discovery well. These data were considered too poor quality to confidently define and map sand bodies using quantitative interpretation techniques. The elastic rock physical properties of brine sands and shale overlap at log-scale on rock physics templates and at seismic scale the hydrocarbonbearing sands can also overlap with variable coals.

Nevertheless, over the past 5-6 years our confidence in quantitative interpretation techniques has significantly improved. Broadband dual azimuth streamer data acquired in 2011 and 2014 provide high quality data. Developments in seismic inversion techniques, specifically direct probabilistic inversion, have allowed more confident lithology prediction. We share results of both deterministic simultaneous AVO inversions and a recent direct probabilistic inversion to lithology. The results of the latter show a significant improvement in prediction of sand distribution.