A New Approach to Pore Pressure Predictions: Generation, Expulsion, and Retention Trio—Case Histories from the Gulf of Mexico

Abstract

A comprehensive framework and fresh perspective to pore pressure prediction methods and algorithms based on the established geological building blocks is presented. Applying the suggested four subsurface zones is the backbone of this pore pressure prediction approach. Determining the boundary of the four subsurface zones utilizing seismic data is crucial for selecting the appropriate method and algorithms for pressure prediction.

This approach divides the previously so-called normally pressured upper section into two zones: namely, hydrostatic and hydrodynamic. Consequently, data in the hydrodynamic section is used to establish the compaction trend and not the entire section above the top of geopressure. The section below the top of geopressure is divided into transition and geopressured zones. This method calculates the compaction trend, rather than graphically displaying it for calibration purposes. Moreover, it eliminates the confusion of extrapolating the predicted effective stress values above the top of geopressure.

In this paper, entrapment represents the main cause of overpressure buildup. Fluid pressure inflation due to stress, aqua-thermal and dewatering processes is the genesis and not the outcome. The effective seal is the main mechanism for creating excess pressure. Investigating possible breach of the seal due to subsurface structural failure is a key objective for pore pressure prediction.

The subsurface hydrogeological zoning greatly impacts the velocity, resistivity and density profiles. Seismic velocity to pore pressure transformation modeling foresees the trio process from generation to expulsion to entrapment before drilling the prospect. The newly introduced subsurface partitions, trio concept, algorithms, and predictive modeling incorporated with the geological setting are supported by case histories from the Gulf of Mexico.

AAPG Datapages/Search and Discovery Article #90219 © 2015 GCAGS, Houston, Texas, September 20-22, 2015