Seismic Modeling Uses & Methods

    Uses of Modeling
    Seismic Modeling can be used to:

    • Certify interpretation is consistent, plausible, and agrees with recorded seismic data

    • Calculate CRP fold and amplitude maps to clarify subsurface coverage and amplitudes in difficult to image areas such as sub-salt plays

    • Decide if prospect is seismically visible and the extent of seismic distortion

    • Determine Amplitude Versus Offset (AVO) response & thin bed tuning effects from logs

    • Show distortion of AVO and Amplitude versus Angle (AVA) effects caused by overlying structure and velocity variations.  Note AVO change caused by salt peak in the simple model below.

    • Ascertain best acquisition parameters

    • Determine velocity field from seismic data by inverse raytracing

    • Convert maps or models from time to depth using inverse raytracing

    •  Investigate seismic processing algorithms and parameters

    Modeling Methods

      Models with enough detail and with correct rock properties are crucial for reliable results. Interpreted horizons from seismic data create the structure of the models. P-wave velocities are derived from seismic data and calibrated to well logs. Density and shear velocity are obtained from well logs or approximated.  Raytracing requires that time models be converted to depth.  Inverse raytracing can be used to create a more accurate model than a vertical shift. In illumination studies, a constant rock property contrast on the reflecting horizon is created that isolates the effects of the overlying structure and velocity variations.

      Raytracing in complex geology, such as subsalt illumination studies, requires offset raytracing that simulates actual shooting geometry.  3-D raytracing is usually required in complex areas.  2-D models can be valuable in understanding effects of variations in individual structure or velocity features (refer to 2-D results above).  Rays are sorted CRP gathers to simulate a 3-D PreSDM process. Results include division into offset bans to assist in AVO analysis and calculation of reflection angles.

Copyright 2002 by Emerald Geoscience Research Corporation