Depth Conversion: Application and Verification of Depth Conversion of 3D and 2D Seismic Data - Case Histories

LaFRENIER, JON E., and JIM DUNKELBERG

A standard process for successful depth conversion and verification of depth conversion requires close interaction between the geologist and geophysicist. The process involves:

1. detailed interpretation of geologically significant time horizons on migrated and stacked time volumes. (The horizons, such as sequence boundaries, unconformities, and faults may be interpreted on 3D and/or 2D seismic data), and

2. iterative map migration and detailed interval velocity analysis, and

3. three dimensional forward modeling and comparison of 3D synthetic volumes to actual 3D seismic data (including amplitude and phase effects).

Interpreted time horizons are converted to depth starting with the shallowest interpreted time horizon. Three dimensional raypath bending is controlled by the dual effects of structural complexity and velocity changes at interfaces (horizons). The horizon's position in depth, its lateral position, structural and stratigraphic reflection geometries and interval velocity is verified via forward modeling using 3D ray-tracing methods. This process is repeated for the total number of horizons to be mapped and on progressively deeper geologic horizons.

The final result -- a validated geologic model -- may be used as input to subsequent pre-stack, model driven depth migration routines for seismic volumes.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.