ABSTRACT: An integrated approach to pressure prediction from 3D seismic data

French, Mike¹, and Dr. Nader Dutta²
(1) Baker Hughes, Western Geophysical, Middlesex, United Kingdom
(2) Baker Hughes, Houston, TX

The capability of predicting subsurface pressure regimes prior to drilling can significantly influence a drilling program from safety issues to well planning and control. In rapid sedimentation areas the prime mechanism for developing overpressure is disequilibrium compaction. This overpressure class influences seismic velocity and density by differences in porosity between normal and overpressured shales and is acoustically measurable. Traditionally pressure prediction is attempted utilising seismic NMO velocities. Seismic NMO velocities suffer from poor temporal resolution and are optimised for stacking. Dix Interval velocity conversion does not correctly handle lateral velocity variations. However, picking velocities with criterion other than stacking can yield valuable low frequency trends. These trends have been found useful for pressure prediction purpose. Seismic data, however, contains two sources of velocity information, reflector traveltime and reflector amplitudes. The procedure described utilises high quality seismic processing to both correctly image reflectors and preserve amplitudes. This enables the use of poststack and prestack seismic inversion techniques so both sources of velocity information can be fully integrated to derive a detailed 3D interval velocity field suitable for pressure prediction work. Calibration from velocity to effective stress and pore pressure is derived by detailed geostatistical analysis of well logs and seismic pseudo-logs. The relationships are then applied to the inverted seismic data to derive a 'volume' of predicted pressure from 3D seismic data. The procedure also has the benefit that the pressure 'volume' can be recalibrated and updated in 'near time' as future wells are drilled and new logging information becomes available.