SWLGS Luncheon Topics
Updated Apr. 5, 2009
April 14, 2009
Surface Seismic Velocity Trends in Subsurface Interpretation- Examples
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.
Carlos Guzman 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 Math. Carlos’ experience as a Shell geophysicist included assignments in seismic acquisition, processing and interpretation.
Several articles on seismic velocity interpretation, written in collaboration with colleagues who shared a similar passion for this subject, have been published. Carlos is interested in the use of non-seismic methods in prospecting.