Effective porosity

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

Design and analysis of tracer tests to determine effective porosity and dispersivity in fractured sedimentary rocks, Newark Basin, New Jersey

Abstract: Investigations of the transport and fate of contaminants in fractured-rock aquifers require knowledge of aquifer hydraulic and transport characteristics to improve prediction of the rate and direction of movement of contaminated ground water. This report describes an approach to estimating hydraulic and transport properties in fractured-rock aquifers; demonstrates the approach at a sedimentary fractured-rock site in the Newark Basin, N.J.; and provides values for hydraulic and transport properties at the site. The approach has three components: (1) characterization of the hydrogeologic framework of ground-water flow within the rock-fracture network, (2) estimation of the distribution of hydraulic properties (hydraulic conductivity and storage coefficient) within that framework, and (3) estimation of transport properties (effective porosity and dispersivity). The approach includes alternatives with increasingly complex data-collection and analysis techniques.

Influences of Sedimentary History on the Mechanical Properties and Microscopic Structure Change of Horonobe Siliceous Rocks

Abstract: As part of the research and development program on geological disposal of high-level radioactive waste Japan Atomic Energy Agency is implementing the Horonobe URL Project. This paper shows the results obtained from the laboratory tests carried out to understand mechanical properties of Horonobe siliceous rocks for site characterization. Accordingly, the relationship among microscopic observation, sedimentary history and mechanical properties of Horonobe siliceous rocks was discussed in this paper. Such laboratory tests as uniaxial compression test, triaxial compression test, isotropic consolidation test were carried out. Uniaxial compression tests were carried out for specimen sampled at about 50 m interval of eleven deep boreholes more than 500 m deep from the ground surface. Triaxial compression tests including isotropic consolidation test were also carried out using cores of the boreholes. The triaxial tests were carried out under drained and undrained conditions since change in pore structure was expected for the sedimentary soft rocks with large effective porosity. Physical and mechanical properties showed significant variations along the burying depth due to dissolution of the minute porosity in diatom occured from increasing of overburden, temperature etc. The consolidated undrained and drained triaxial compression tests showed different behaviors of strain-softening, pore pressure and dilatancy between diatomaceous and siliceous mudstones. Stress-strain behavior changed from strain-softening to ductile behavior under high confining pressure and pore pressure increased gradually even after peak strength for diatomaceous mudstone. On the other hand, for siliceous mudstone strain-softening behavior was observed and pore pressure decreased rapidly after peak stress regardless of confining pressure value. Diatomaceous mudstone yielded under hydrostatic pressure of 10 MPa in isotropic consolidation test. This yielding was regarded as pore collapse based on the variation of hydraulic conductivity which was estimated from variation of volumetric strain in isotropic consolidation test, effective porosity and microscopic observation before and after the yielding.

Chapter 7 Carbonate Oil Reservoir Rocks

Abstract: Summary Half or more of the world's petroleum is produced from carbonate reservoir rocks. The oil-reservoir characteristics of carbonate rocks are largely functions of porosity and relative permeability, which, in turn, have been affected by initial composition of the rocks and their subsequent history. Porosity of carbonate rocks may be arbitrarily divided into (1) primary porosity (formed during deposition), (2) secondary porosity (formed by solution, fracturing or other changes after deposition), and (3) sucrose dolomite porosity (resulting from replacement of calcite by dolomite). Primary porosity may in turn be subdivided into (a) framework porosity resulting from pores that remained as a result of the “sheltering” effect of rigid or loosely-aggregated frameworks, (b) mud porosity, consisting mostly of minute pores that remained in partly compacted carbonate mud that was subsequently lithified, and (c) sand porosity consisting of voids between sorted sand and gravel-sized carbonate particles. Most primary pores have been modified by solution (and cementation). Consequently, there is no sharp dividing line between primary porosity and secondary porosity resulting from solution. Sucrose dolomite porosity is important in many oil reservoirs. In these rocks, porosity and permeability have been strongly influenced by composition of the original carbonate sediment and the degree to which the rock has been replaced by sucrose dolomite. For example, in certain Devonian rocks in west Texas, which originally consisted of varying proportions of lime mud and of crinoid-stem fragments, the greatest porosity occurs in rocks that have been most highly dolomitized. Here, the percentage of dolomite tends to be greatest in rocks which originally contained about 45% lime mud and 55 % crinoid-stem fragments. The performance of carbonate reservoirs depends to a substantial degree on shapes and dimensions of pores and their geometric arrangement with respect to each other. Under oil-reservoir conditions, pores in rocks are generally occupied by either water or oil. Ordinarily, the reservoir rock is water wet, that is, each rock grain is surrounded by a thin film of water, and oil is generally the non-wetting phase. Isolated oil globules ordinarily will not migrate through the rock because the interfacial tension between water and oil is so high that the globules will not pass through the throats of pore interconnections. Before the oil can move as a separate phase, the displacement pressure between the oil-water interface must exceed the entry pressure of the pore interconnections. The displacement pressure is influenced principally by buoyancy, whereas entry pressure depends on the interfacial tension between water and oil, and on pore geometry. The minimum height of an oil column necessary for buoyant rise through a water-wet carbonate rock thus partly depends on the diameters of throats of pores and diameters of the interiors of pores. The reservoir performance of carbonate rocks may be predicted by injecting mercury into cores from reservoirs. Mercury, a non-wetting fluid, is forced into the core sample under increasing pressure. A graph of the data, showing injection pressure, versus cumulative volume of mercury injected, is an effective guide to the conditions required for oil to move in the rock. Ancient depositional environments exert strong influence on carbonate deposits formed in them, and, in turn, have subsequent effect on oil-reservoir conditions in carbonate rocks. Many examples could be cited. In Mississippian carbonate reservoirs in southeastern Saskatchewan, oolitic and pseudo-oolitic limestones interpreted to have been formed through chemical precipitation in a barrier bank environment, serve Iocally as excellent, highly permeable oil reservoirs. In west Texas, the Pennsylvanian-Permian Horseshoe atoll is a horseshoe-shaped mass of limestone about 90miles across in an east-west direction and 70 miles from north to south. It is interpreted to be analogous to modern reef atolls of the East Indies. In the Paradox Basin of southeastern Utah, limestone lenses composed largely of leaflike calcareous Algae serve as oil reservoirs. In Alberta, much oil is produced from Devonian rocks in which favorable reservoir conditions are closely associated with stromatoporoids and calcareous Algae. The geographic outlines of certain oil fields in Alberta, such as Red-water field, are essentially parallel to the trends of ancient organism communities. Thus, there is strong incentive to interpret ancient carbonate environments and organism communities, and to understand their effects on oil-reservoir properties.