Pore water pressure

About: Pore water pressure is a research topic. Over the lifetime, 11455 publications have been published within this topic receiving 247670 citations. The topic is also known as: pwp.

Generation and maintenance of pore pressure excess in a dehydrating system 2. Theoretical analysis

Abstract: Fluid is released by dehydration reactions during prograde metamorphism. If the dilation of the pore space is insufficient to provide storage for all the released fluid, then pore pressure excess is generated. Whether the excess can be maintained over long duration hinges on the hydraulic transport properties of the rock. Motivated by recent experimental and microstructural observations, we developed a theoretical model which incorporates dehydration and porosity production rates as source terms in the hydraulic diffusion equation. The permeability was assumed to be sensitively dependent on the porosity. The finite difference technique was used to analyze the generation and maintenance of pore pressure excess for several types of boundary conditions of importance in laboratory and crustal scales. Analytic estimates of the pore pressure anomaly were also obtained. The model is in reasonable agreement with experimental observations on dehydration-induced weakening and transient buildup of pore pressure in a nominally drained sample. It provides hydrogeological constraints on the development of pore pressure excess in metamorphic and tectonic settings. The maintenance of a nearly lithostatic pore pressure requires the permeability to be below a critical value which increases with increasing dehydration rate and thickness of the dehydrating layer, and with decreasing porosity production rate. If these constraints are not met, the pore pressure excess can only occur as a transient pulse, the amplitude of which may approach lithostatic for sufficiently large dehydration rate and layer thickness, or sufficiently low permeability.

Hydrological modeling of the Martian crust with application to the pressurization of aquifers

Abstract: [1] We develop a hydrological model of the Martian crust, including both ancient heavily cratered terrains and younger basaltic and sedimentary terrains. The porosity, permeability, and compressibility are represented as interdependent functions of the effective stress state of the aquifer, as determined by the combination of the lithostatic pressure and the fluid pore pressure. In the megaregolith aquifer model, the crust is modeled as a 2 km thick megaregolith, composed of lithified and fractured impact ejecta, overlying the impact-fractured and partially brecciated basement rock. The hydraulic properties depend primarily upon the abundance of breccia and the compressional state of the fractures. The porosity ranges from approximately 0.16 at the surface to 0.04 at a depth of 10 km, with a sharp discontinuity at the base of the regolith. Thepermeability variesfromapproximately10 � 11 m 2 atthesurfaceto10 � 15 m 2 atdepthsof 5 km or more and is strongly dependent upon the fluid pore pressure. The hydrologic properties of basaltic and sedimentary aquifers are also considered. These parameters are used to model the fluid pressures generated beneath a thickening cryosphere during a postulated dramatic cooling of the climate at the end of the Noachian. As a result of a negative feedback between the fluid pore pressure and the permeability, it is more difficult thanpreviouslythoughttogenerateporepressuresinexcessofthelithostaticpressurebythis mechanism.Theproductionoftheoutflowchannelsastheresultofsuchaclimaticchangeis deemed unlikely.