Effective porosity

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

A Method for Estimating Effective Porosity and Ground‐Water Velocity

Abstract: Estimates of ground-water velocity, based either on Darcy's law or on the single-well drift and pumpback tracer method, require prior knowledge of effective porosity. That is, after field data have been collected, the equation for ground-water velocity, using either method, still contains the two unknowns, velocity and porosity. If the local hydraulic gradient is known and if a drift and pumpback tracer test is conducted at a well whose hydraulic conductivity has been determined, two independent functional relationships between velocity and porosity are established. By treating these functions as nonlinear simultaneous equations, a unique solution for the local velocity and porosity can be obtained.

Lithology Dependence of Porosity in Slope and Deep Marine Sediments

Abstract: Compilation of porosity data from 11 Ocean Drilling Program legs and 53 sites show that compaction in deep marine to upper-slope sediments is, at least in part, a function of both burial depth and lithology. Overall porosities range from 4 to 94%. Despite the broad range of porosities, there is an exponential trend toward decreasing porosity with depth. Comparison among samples dominated (90 to 100%) by each of six lithologies, based on grain size and composition, reveals the lithology dependence of compaction, except for biogenic silt-size sediments and clastic sands. In the former case, this may, in part, be due to mixing of calcareous and siliceous nannofossils. Clay-size clastic sediments show a clear change from rapid porosity reduction in the top 172 meters (porosity = 82.7 e−depth/430) to less pronounced loss of porosity below (porosity = 61.4 e−depth/1671). The remainder of the lithologies, silt (porosity = 75.5 e−depth/1091), biogenic sand (porosity = 88.5 e−depth/1338) and micrite (porosity = 69.5 e−depth/1235) show a good to strong exponential reduction of porosity with depth. These relations compare well with literature studies, taking into account the less pure nature of the lithologies used in this work. The silt compaction curve is unique; no previous studies of porosity separated silt from other grain sizes. Most sediment samples are of mixed grain sizes and types. The lithology-based porosity-depth relations were used to test four approaches to decompaction in mixed-lithology sediment used in backstripping. All methods generated porosity estimates that correlated strongly to the observed values, with correlation coefficients ranging from 0.629 to 0.686. These methods that have been used for years are, for the first time, shown to be valid.

Porosity and Permeability in Sediment Mixtures

Abstract: Porosity in sediments that contain a mix of coarser- and finer-grained components varies as a function of the porosity and volume fraction of each component. We considered sediment mixtures representing poorly sorted sands and gravely sands. We expanded an existing fractional-packing model for porosity to represent mixtures in which finer grains approach the size of the pores that would exist among the coarser grains alone. The model well represents the porosity measured in laboratory experiments in which grain sizes and volume fractions were systematically changed within sediment mixtures. Permeability values were determined for these sediment mixtures using a model based on grain-size statistics and the expanded fractional-packing porosity model. The permeability model well represents permeability measured in laboratory experiments using air- and water-based permeametry on the model sediment mixtures.

Geomechanical and geochemical effects on sandstones caused by the reaction with supercritical CO 2 : an experimental approach to in situ conditions in deep geological reservoirs

Abstract: The geochemical and geomechanical behaviour of reservoir rocks from deep saline aquifers during the injection and geological storage of CO2 is studied in laboratory experiments. A combination of geochemical and geomechanical studies was carried out on various sandstones from the North German Basin. After the mineralogical, geochemical and petrophysical characterization, a set of sandstone samples was exposed to supercritical (sc)CO2 and brine for 2–4 weeks in an autoclave system. One sample was mineralogically and geochemically characterised and then loaded in a triaxial cell under in situ pressure and temperature conditions to study the changes of the geomechanical rock properties. After treatment in the autoclaves, geochemical alterations mainly in the carbonate, but also in the sheet silicate cements as well as in single minerals of the sandstones were observed, affecting the rocks granular structure. In addition to partial solution effects during the geochemical experiments, small grains of secondary carbonate and other mineral precipitations were observed within the pore space of the treated sandstones. Results of additional geomechanical experiments with untreated samples show that the rock strength is influenced by the saturation degree, the confining pressure, the pore fluid pressure and temperature. The exposure to pure scCO2 in the autoclave system induces reduced strength parameters, modified elastic deformation behaviour and changes of the effective porosity in comparison to untreated sandstone samples. Experimental results show that the volume of pore fluid fluxing into the pore space of the sandstones clearly depends on the saturation level of the sample.