Pitfalls in Seismic Time to Depth Conversion for Geological Modelling

The objective of geological modelling is to build a realistic image of the subsurface by representing both the structural features and the lithological properties of the units. Geological model building is the basic step of basin and reservoir modelling studies. In this frame, the main input information are usually derived from seismic interpretation : e.g. horizon maps (top and base of geological units), thickness maps, facies maps… Various techniques are available to convert these information from time to depth, their accuracy strongly depends on the complexity of structural and stratigraphic variations. This paper aims at illustrating that accurate time to depth conversion of seismic results can reduce the propagation of uncertainties from geophysical to geological interpretations, limiting the ambiguities in further modelling studies. Three major pitfalls induced by inadequate time to depth conversion and giving drastic misfits in estimation of reservoir volume, connectivity network or facies distribution, are presented (geometrical issues, fault characteristics, well to surface data calibration).