Abstract: Time to Depth Conversion: Relating Seismic Data to the Real Earth

LITTMAN, MARK, and ALEX LITVIN

There are two main depthing challenges: accurate Time to Depth conversion of interpreted time arrivals and interpretation of depth images in structurally complex areas where conventional time migration techniques fail to allow reliable interpretation. Both these goals can only be achieved by deriving a reliable velocity depth model. It will be shown how seismic velocities can be integrated with well velocity data to produce the robust Earth Model necessary for success in sub-surface prediction.

Seismic velocities and well velocities are complementary data types. Well velocity is reliable but sparsely and irregularly distributed, only sampling particular geological regimes. While seismic derived velocities tend to be less reliable but more dense and regularly distributed, filling in the gaps between well locations.

Using real data examples the main technologies for extracting seismic velocities will be described. It will be shown how cross plot interpretation can be used for extracting additional geological information as well as conditioning and calibration of the seismic velocity data.

Seismic velocities can be used to aid interpolation between well data. Due to anisotropy and other factors seismic velocities can differ from well velocities. However, seismic velocities show regional trends between well locations and these trends can then be calibrated to the available well information using cross plotting techniques.

Seismic velocities can be used for depth imaging in order to provide round for reliable interpretation when time imaging fails. To achieve well consistent depth results the depth images have to be re-scaled with a layer velocity field integrating well and seismic data.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria