Effective porosity

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

Bacteriophage Transport in Sandy Soil and Fractured Tuff.

Abstract: Bacteriophage transport was investigated in laboratory column experiments using sandy soil, a controlled field study in a sandy wash, and laboratory experiments using fractured rock. In the soil columns, the phage MS-2 exhibited significant dispersion and was excluded from 35 to 40% of the void volume but did not adsorb. Dispersion in the field was similiar to that observed in the laboratory. The phage f2 was largely excluded from the porous matrix of the two fractured-rock cores studied, coming through 1.2 and 2.0 times later than predicted on the basis of fracture flow alone. Because of matrix diffusion, nonsorbing solutes were retarded by over a factor of three relative to fracture flow. The time for a solute tracer to equilibrate with the porous matrix of 6.5-cm-diameter by 25-cm-long cores was measured in days. Results of both granular-medium and fractured-rock experiments illustrate the inability of a solute tracer to provide estimates for dispersion and effective porosity that are applicable to a colloid. Bacteriophage can be used to better estimate the maximum subsurface transport rate of colloidal contaminants through a porous formation.

Diagenesis and Preservation of Porosity in Norphlet Formation (Upper Jurassic), Southern Alabama

Abstract: Sandstones of the Norphlet Formation (Upper Jurassic) in the vicinity of Lower Mobile Bay, Alabama, have porosities greater than 20% and permeabilities up to about 1 darcy at depths of more than 20,000 ft (6,096 m). Typically, pre-Tertiary sandstones buried to such depths have approximately 6% (±2%) porosity; thus, deep Norphlet sandstones contain up to 14% "excess" porosity. This porosity is largely intergranular and appears to be preserved primary porosity. When the diagenetic scenario for the Norphlet is reconstructed in a time-temperature framework, it is apparent that porosity preservation is not the result of any single diagenetic event, but is due to a continuous series of diagenetic conditions that overlapped in time. The most important of these circumstances were the following. (1) The lack of pervasive early calcite or anhydrite cements found in the large eolian dunes (10-300 ft or 3-91 m high) that comprise the best Norphlet reservoirs. This lack of cement may have set the stage for subsequent events by keeping open pathways through which fluids were later able to efficiently contact the sandstone. (2) Early grain-coating clay/iron oxide rims reacted to form chlorite in the 176°-248°F (80°-120°C) thermal wind w. The grain-rimming chlorite may have inhibited subsequent quartz cementation. Up to 10.5% porosity may be due to the porosity preserving effect of chlorite. (3) Migration of hydrocarbons and development of geopressures, beginning at temperatures as low as 230°F (110°C), retarded further cementation. Up to 4.5% porosity may be due to the combined effects of hydrocarbons and geopressures. (4) A series of CO2-generating reactions occurred, including decarboxylation of organic acids, thermal cracking of liquid hydrocarbons, and thermochemical sulfate reduction. As a result of these reactions, late carbonate cements were not abundant. Thermochemical sulfate reduction (275°-356°+F or 135°-180°+C) has been of particular importance in the deep Norphlet. Reaction of hydrocarbons with anhydrite has resulted in the local removal of nodular anhydrite and has also affected gas quality (i.e., H2S content). The preserved porosity in Norphlet sandstones is the result of a combination of circumstances. The fact that these conditions overlapped in time-temperature space may be as important as any single factor.

Critical porosity; the key to relating physical properties to porosity in rocks

Abstract: Many classes of rock such as sandstones, dolomites, chalks, and cracked igneous rocks have each a distinct characteristic porosity above which the material behaves as s suspension. The porosity at which this system changes, or transforms from isostress to solid load-bearing is defined here as the critical porosity {phi}{sub c}. It is easy to envision that at {phi}{sub c} not only the mechanical moduli, but also other properties such as strength and electrical conductivity, may also undergo transformations. Consequently, the critical porosity must be a fundamental property of a given porous system, not just of one of its physical properties. The observed values of {phi}{sub c} range from .005 for cracked granites to .30 or .40 for limestones, dolomites and sandstones, .60 for chalks and .90 for volcanic glasses. The data suggest that (1) A critical porosity value {phi}{sub c} exists which is typical of a given class of porous materials. Each class is defined on the basis of its common mineralogy or diagenetic porosity reduction processes. (2) Given {phi}{sub c} it may be possible to closely approximate the relation between porosity and velocity, over the entire range of porosity, with a modified mixture relation, in which the mixed componentsmore » are the pure solid on one end, and a critical suspension on the other. (3) Without {phi}{sub c}, theory cannot yield reliable or useful velocity-porosity relations.« less