Geologically Driven Pore Pressure Prediction from Seismic Velocity Data - Theory

Swarbrick, Richard ¹; Lahann, Rick ²; O'Connor, Stephen ¹; Hoskin, Ed ¹; Green, Sam ¹
(1) GeoPressure Technology, Durham, United Kingdom. (2) Indiana University, Bloomington, IN.

Seismic velocity data is frequently used world-wide to predict pore (or fluid) pressures. The advantage is that these data may be all that are available in frontier areas, where there are no well penetrations, or drilling is to be deeper than existing wells. However, there is a common misconception that pore pressures derived in this manner can yield accurate results for all basins and geological scenarios. Seismically-derived velocity data will gives accurate results in areas where sedimentation rates are high, temperatures are low and lithology is shale-dominated, typically Tertiary Delta such as the Pliocene in the Nile Delta and the Agbada Formation in the Niger Delta. In such areas, velocity data are utilized to detect porosity anomalies related to pressure using standard techniques and relationships derived during successive exploration phases of the Gulf of Mexico. Pore pressure prediction will not, however, be reliable using these techniques in basins where pressures are generated by mechanisms other than disequilibrium compaction, basins other than extensional, where temperatures exceed approximately 100 - 120oC, and where lithologies are non-clastic; in these environments, errors can be of the magnitude of 1000’s psi and result in loss of well control and serious drilling problems and safety.

In this paper we review those areas where seismic-based pore pressure prediction is likely to be reliable and where application of standard techniques will be suspect. We will discuss those processes that may result in additional pressure generation such as load transfer, and offer solutions for a range of scenarios.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.