Porepresset

Porepresset refers to the pressure exerted by fluids within the pore spaces of a rock or soil. In geoscience and related fields it is more commonly called pore pressure. It characterizes the hydraulic state inside a geological formation and affects the mechanical behavior of the rock or soil through its influence on effective stress.

In terms of mechanics, the effective stress is the total stress minus the pore pressure (sigma prime = sigma - p). Higher pore pressure lowers the effective stress and can reduce strength, promote deformation, or trigger failure. Pore pressure is often discussed in relation to hydrostatic (normal) conditions, overpressure (abnormal) conditions, and, less commonly, underpressure. Overpressure occurs when fluid generation, rapid sedimentation, or restricted drainage prevent fluids from escaping, leading to elevated pore pressures relative to depth.

Measurement and estimation methods vary. Direct measurements are obtained from downhole pressure sensors in boreholes. Indirect estimates use well logs, seismic velocity data, and regional geology. Common predictive approaches include empirical correlations that compare shale sonic or density trends with normal compaction, such as Eaton-type methods, which help anticipate geopressure zones to guide safe mud-weight design during drilling.

Pore pressure is significant in petroleum engineering, geothermal and groundwater hydrology, and geotechnical engineering. In drilling, accurate estimates reduce the risk of kicks and blowouts. In soils and rocks, elevated pore pressure weakens shear strength and can influence slope stability, liquefaction potential, and consolidation behavior.