Abstract

Permeability and geologic time are the primary controlling factors for the generation and dissipation of overpressures. With respect to increasing depth, pressure gradients within any layer may increase, decrease, or remain essentially constant. Pore pressure gradients also vary laterally as a response to changes in permeability, which do not always correspond to seismic or correlation surfaces. In some cases, pressure may not respond at all to the presence of a fault, indicating that the fault zone is permeable and that either vertical or lateral fluid flow has allowed pressure to equilibrate across the fault zone. Some faults act as pressure barriers where an overpressured seal does not allow for fluid flow across the fault zone. Barostratigraphy objectively describes the present-day results of the subsurface processes that create overpressures and those that allow abnormal pressures to be maintained and dissipate. Additionally, barostratigraphy provides a formal method to better categorize pressure compartmentalization by providing a framework for the analysis of the stratigraphic nature of subsurface pressure compartments. It is a classification that systematically arranges and partitions subsurface units based on their inherent properties and pressure attributes. These units are identifiable based on observable criteria. They are correlatable, mappable, and useful in identifying the current pressure conditions in all or part of a basin. The prediction of pore pressure at proposed well locations can be optimized by the use of barostratigraphy, which aids in the analysis of subsurface pressure magnitudes and variation, and in basin modeling. Additionally, an understanding of the hydrocarbon distribution in an area (and prospect risking) is enhanced, as is the analysis of seismic velocities and their impact on imaging due to the close relationship between velocity and effective stress.

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