Philip D. Heppard¹, Martin L. Albertin¹, Bruce E. Wagner¹, Deedee J. Bettencourtt¹
(1) BP Amoco, Houston, TX

Abstract: Difficulties in Pressure Prediction Using Seismic Velocities Due to Anisotropy, Velocity Insensitivity, and Inadequate Geologic Prediction

Pore pressure prediction is a significant tool for reducing cost and improving safety in exploratory drilling, and in finding viable hydrocarbon seals. Using seismically derived interval velocity for predicting pressure away from well control depend on both the accuracy of the interval velocities, and an understanding of the geologic conditions of the area. The accuracy of seismic derived interval velocities depends on acquisition design, geologic complexity, data quality, anisotropy, the depth and scale of investigation, seismic processing, and the skill and experience of the seismic processor. Three examples illustrate some of the difficulties in pressure prediction. At the King area, deep water Gulf of Mexico, seismic anisotropy in the shallow Micoene section caused us to overestimate interval velocities and underpredict pore pressure. Lack of velocity sensitivity prohibited us from detecting a rapid velocity decrease in the deep, highly overpressured lower Miocene through Cretaceous section. In deep water Trinidad, uncertainty as to the pressure implications of slow Pleistocene clastic sediments led to two predictions. In the Nile Delta, Egypt, the fast velocity trend of the sand dominated shallowest section is could be misleading. An additional complexity is the presence of thin sandstone reservoirs with variable lateral continuity and structural relief. The pressure in these porous and permeable reservoirs must be estimated by redistributing the overpressure observed in the bounding shales throughout their entire areal extent.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana