Are PSDM Depth Interpretations Reliable?

PSDM velocities underlying PSDM depth interpretations are optimized for depth imaging, not for depth conversion.

PSDM velocities must then be analyzed in space for the consistency of their lateral variations before being considered for depth interpretation. Moreover they require spatial conditioning to extract their contributing part to the depth conversion.

Spatial quality assessment and conditioning of PSDM velocity data makes use of stochastic modelling (or geostatistics) for “best estimating” the spatial components of the PSDM velocity data that contribute to depth conversion and interpretation, and about “filtering-out” the spatial components that are considered as non contributing.

As a result from a stochastic model, conditioned PSDM velocities are systematically associated with reliable confidence intervals, enabling geophysicists to optimize their contribution before engaging in depth conversion and interpretation.

A North Sea case study illustrates the topic and shows how spatial quality assessment and conditioning of PSDM velocity helped to anticipate a 200m depth error on a new exploration well with deep sub salt target, and reduced it to a less than 40m error, in line with the +/- 100m depth confidence interval computed from the stochastic model.