Porosity and Formation Pressure Prediction from Seismic Data

Ruben D. Martinez

Seismic porosity and formation pressure logs are derived from seismic data exploiting novel characteristics of wavelet deconvolution and seismic inversion by modeling.

In the first stage of wavelet deconvolution, the system wavelet is removed, and data are migrated to their true position. Thereafter, postmigration processing is performed in a deterministic manner using constraints derived from seismic and well data. The final result is the band-limited version of the reflectivity function. Subsequently, seismic inversion by modeling is accomplished iteratively, using the recursion expression that relates the acoustic impedance with the reflection coefficient. Missing frequencies between the high-frequency cut of the low-frequency acoustic impedance model and the low-frequency cut of the seismic data are also recovered iteratively. This feature provides better resolution through the acoustic impedance logs in time and depth. Velocity and pseudodensit logs are then derived using a relationship between densities and sonic velocities.

Seismic porosity and formation pressure are computed against depth using the velocity and pseudodensity logs. Seismic porosities are calculated using bulk pseudodensities. Appropriate depth-variant constraints (matrix and fluid densities, shaliness factors) are generated from well-log data and gridded to produce constraint profiles in common-depth-point depth space. Formation pressure logs are calculated assuming that compressional velocity, density, and depth are proportional to formation pressure. The seismic porosity and formation pressure logs may be then interpreted to delineate reservoirs and to detect abnormally pressured zones. An example using real data illustrates the complete procedure followed for seismic porosity and formation log calculations.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.