Effective porosity

About: Effective porosity is a research topic. Over the lifetime, 1199 publications have been published within this topic receiving 26511 citations.

Porosity and permeability development in mechanically compacted silt‐kaolinite mixtures

Abstract: Summary Prediction of porosity and permeability in mudstones are challenging because of the uncertainties associated with textural and mineralogical composition. This study investigates the development of porosity and permeability in thirteen mechanically compacted brine-saturated synthetic mudstones consisting of silt and kaolinite mixtures. The drained uniaxial mechanical compaction tests were performed under room temperature and atmospheric pressure. Total porosity and vertical permeability (parallel to the direction of applied stress) were measured continuously for each sample under increasing effective stress up to 50 MPa. Results show that mineralogy is a dominant factor controlling the development of porosity and permeability in silt-clay mixtures. Kaolinite-dominated samples have much lower porosity and permeability compared to silt-dominated samples. At 20 MPa effective stress that corresponds to about 2 km depth of burial of normally compacted basin, the pure kaolinite sample was compacted to about 20% porosity whereas the pure silt sample had retained 35% porosity. The permeability of pure kaolinite and silt samples were about 0.003 and 0.2 mD respectively at the same effective stress. The porosity and permeability reduction were not systematic with increasing kaolinite content in silt aggregates or vice versa. The porosity and permeability difference between pure silt and pure kaolinite aggregates were relatively less at low effective stresses but increased significantly with increasing effective stress. At high effective stresses the permeability was 2-3 orders of magnitude lower in pure kaolinite than in pure silt. Calculating permeability in mudstones from porosity without considering mineralogy will therefore introduce significant error in permeability estimation. Our experimental results provide valuable constraints on porosity-stress/depth, permeability-stress/depth and porosity-permeability relationships for shallow mudstones that will have practical use for basin modelling, pore pressure prediction and fluid flow modelling in shallower part of the basins (<80-100 0 C) where mechanical compaction is the dominant process.

The Effect of Zones of High Porosity and Permeability on the Configuration of the Saline-Freshwater Mixing Zone

Abstract: Coastal karst aquifers have highly variable distributions of porosity and permeability. The ability to assess the volume of aquifer occupied by freshwater in coastal karst aquifers is limited by both the lack of understanding of the effect that regions of cavernous porosity and permeability have on the configuration of the saline-freshwater mixing zone and by the limited knowledge of the location of the cavernous regions. A dual-density ground-water flow and solute transport model was used to explore the effect that the depth, lateral extent, and proximity to the coast of zones of high porosity and permeability has on the configuration of the saline-freshwater mixing zone. These aquifer heterogeneities tend to shift the mixing zone upward relative to the position it would have in aquifers with homogeneous porosity and permeability. Zones of high porosity and permeability located at positions shallow in the aquifer or nearer to the coast had the greatest effect. In fact, for the conditions modeled, position was more important in modifying the configuration of the mixing zone than was changing the ratio of the intrinsic permeability of the cavernous zone to the aquifer matrix from 100 to 1000. Modeling results show that ground-water flow is concentrated into the zones of high porosity and permeability and that flow configuration results in steep salinity gradients with depth. Field observations of the location of the halocline and of step changes in ground-water composition coincident with regions of cavernous porosity in coastal karst aquifers corroborate the model results. In a coastal setting with saline water intruding into an aquifer, the effect of cavernous porosity and associated high permeability is to decrease the volume of aquifer in which freshwater occurs by a greater degree than would occur in an aquifer with homogeneous porosity and permeability.

Pore Pressure Diffusion and the Hydrologic Response of Nearly Saturated, Thin Landslide Deposits to Rainfall

Abstract: Previous workers have correlated slope failures during rainstorms with rainfall intensity, rainfall duration, and seasonal antecedent rainfall. This note shows how such relationships can be interpreted using a periodic steady-state solution to the well-known linear pressure diffusion equation. Normalization of the governing equation yields a characteristic response time that is a function of soil thickness, saturated hydraulic conductivity, and pre-storm effective porosity, and which is analogous to the travel time of a piston wetting front. The effects of storm frequency and magnitude are also successfully quantified using dimensionless attenuation factors and lag times.