Integrating Surface Seismic Velocity into Subsurface Interpretation
Speaker: Carlos E. Guzman
Geophysicist
LLOG Exploration
Metairie
Louisiana
Biography:
Carlos worked for Shell Exploration and Production Company as a Geophysicist from 1977 to 2007 after attending the University of New Orleans, and Purdue University where he studied Physics and Mathematics. His experience as a Shell Geophysicist included assignments in seismic acquisition, processing and interpretation, onshore and offshore, Gulf of Mexico.
He dedicated considerable effort to the study of seismic velocities and their interpretation. Several articles, written in collaboration with colleagues who shared a similar passion for this subject, have been published. He is also interested in the use of non-seismic methods in prospecting.
Carlos currently works as a Consultant for LLOG Exploration Co., a sponsor of this meeting.
Abstract:
The role played by accurate seismic velocity measurements in imaging is well known. Image quality is degraded when sub optimal velocity measurements are used in stacking the data; accurate seismic interval velocity models are critical for pre-stack depth imaging. In both processing strategies, flat offset gathers are used to validate the velocity used.
The seismic velocities are not just for imaging and processing, however. Surface seismic velocity measurements yield sub surface velocity trends that can be calibrated with well or ground velocities to generate pore pressure, stress, and fracture pressure volumes for well planning and interpretation.
The talk begins with calibrations of seismic and ground velocity trends, and presents examples to illustrate that seismic velocity trends are an essential component of the overall interpretation.
Seismic velocities discussed in this presentation are measured using the standard semblance method on pre stack time migrated data, and interval velocities are computed using the Dix formula. Dense sampling of the semblances, implemented using an auto volume measurement process, gives the best results. When coarser sampling is used, the measurements are made by the interpreter to improve their quality.
Seismic velocity-based attribute volumes, built from densely sampled semblance measurements, are powerful diagnostics that need to be available early in the interpretation process. Interpreter input is needed to insure proper conditioning of the pre stack data, careful attention to sampling and smoothing of the velocity measurements, and calibration to well velocities.