Relationships between Pore Pressure and Stress in Different Tectonic Settings

摘要

This chapter discusses the effect of different overpressure mechanisms and tectonic settings on the pore-pressure-stress relationship. We demonstrate that the two are intrinsically linked and that a change of one affects the other. Vertical and horizontal stress increases result in overpressuring in normally consolidated low-permeability sediments; overpressuring due to tectonic stresses can be far higher than that generated by rapid sedimentary loading. Pore-pressure increase, however, causes a change in the stresses and fracture gradient if deformation is constrained in any direction. We present a theoretical model, based on field observations, which suggests that overpressuring by a fluid source tends to render the stresses more isotropic. The variability of porosity and pore-pressure-stress relationships for different overpressure mechanisms and tectonic settings means that methods that consider risk and uncertainty in pressure-fracture gradient prediction need to be developed for geologically complex areas.