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Effective porosity

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


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TL;DR: In this article, a mathematical model for predicting porosity histories due to quartz overgrowth in quartz-rich sandstone reservoirs has been developed, which is based on fluid flow through initially porous, unlithified sands in which the fluid phase is saturated with Si(OH)4 and is always in equilibrium with quartz.
Abstract: A mathematical model for predicting porosity histories due to quartz overgrowth in quartz-rich sandstone reservoirs has been developed. The model neglects secondary dissolution porosity and other diagenetic processes such as compaction and precipitation of carbonate and clay minerals. Nevertheless, the model is straightforward and easy to use to calculate porosity. The calculated porosity corresponds to measured porosity of simple quartz-cemented sandstones in 27 wells in North and South America. The model is based on fluid flow through initially porous, unlithified sands in which the fluid phase is saturated with Si(OH)4 and is always in equilibrium with quartz. As the continuously circulating fluid migrates updip toward the basin edge, it cools, and quartz precipitates into the pore spaces causing a loss of porosity. Basinal fluid velocities may be calculated assuming (1) thermal convection and (2) hydrostatic pressure due to recharge at the edge of the basin. Porosity diagrams relating porosity to geothermal gradient, burial rate, and depth of burial are compared to thermal maturation models of source rocks, fluid flow history, and grain-size distribution. The rate of porosity reduction depends on the following variables in decreasing order of significance: buria rate, age, initial porosity, basin size (dip angle), fluid dynamics, initial permeability, and geothermal gradient.

53 citations

Journal ArticleDOI
TL;DR: In this article, the influence of matrix diffusion on the trapping mechanisms relevant for the long-term fate of CO2 injected in fissured rocks was studied. And the simulations showed that dissolution trapping and hydrodynamic trapping are more effective in double porosity aquifers than in an equivalent porous media.

53 citations

Journal ArticleDOI
TL;DR: In this paper, the authors measured the porosity of the Biscayne aquifer and found that the relative ease of contaminant movement to municipal supply wells is much greater than previously considered.
Abstract: Proposed expansion of extractive lime-rock mines near the Miami–Dade County Northwest well field and Everglades wetland areas has garnered intense scrutiny by government, public, environmental stakeholders, and the media because of concern that mining will increase the risk of pathogen contamination. Rock mines are excavated to the same depth as the well field's primary producing zone. The underlying karst Biscayne aquifer is a triple-porosity system characterized by (1) a matrix of interparticle porosity and separate vug porosity; (2) touching-vug porosity that forms preferred, stratiform passageways; and, less commonly, (3) conduit porosity formed by thin solution pipes, bedding-plane vugs, and cavernous vugs. Existing ground-water flow and particle tracking models do not provide adequate information regarding the ability of the aquifer to limit the advective movement of pathogens and other contaminants. Chemical transport and colloidal mobility properties have been delineated using conservative and microsphere-surrogate tracers for Cryptosporidium parvum . Forced-gradient tests were executed by introducing conservative tracers into injection wells located 100 m (328 ft) from a municipal-supply well. Apparent mean advective velocity between the wells is one to two orders of magnitude greater than previously measured. Touching-vug, stratiform flow zones are efficient pathways for tracer movement at the well field. The effective porosity for a continuum model between the point of injection and tracer recovery ranges from 2 to 4 percent and is an order of magnitude smaller than previously assumed. Existing well-field protection zones were established using porosity estimates based on specific yield. The effective, or kinematic, porosity of a Biscayne aquifer continuum model is lower than the total porosity, because high velocities occur along preferential flow paths that result in faster times of travel than can be represented with the ground-water flow equation. Tracer tests indicate that the relative ease of contaminant movement to municipal supply wells is much greater than previously considered.

52 citations

Journal Article
TL;DR: In this article, a triple porosity model for vuggy and fractured reservoirs was proposed and a new technique was presented for these-types of reservoirs that is shown to hold for all combinations of matrix, fracture and non-connected vug porosities.
Abstract: The analysis of vuggy and fractured reservoirs has been an area of significant interest in the past few years. Several researchers have studied the characterization of these reservoirs using dual porosity models and have looked for means of estimating values of the dual porosity exponent m for use in calculations of water saturation. There are instances where the reservoir is composed mainly of matrix, fractures and non-connected vugs. In these cases a triple porosity model appears more suitable for petrophysical evaluation of the reservoir. A new technique is presented for these- types of reservoirs that is shown to hold for all combinations of matrix, fracture, and non-connected vug porosities. At low porosities, the fractures dominate and the m values of the composite system tend to be smaller than the porosity exponent of the matrix (m b ). As the total porosity increases, however, the effect of the non-connected vugs becomes more important and m of the triple porosity system can become larger than m b . To the best of our knowledge a solution to the problem associated with the triple porosity exponent has not been addressed previously in the petrophysical literature. This research is inspired by the availability of modem magnetic resonance, micro-resistivity and sonic image tools that permit reasonable characterization of complex reservoirs. The use of the triple porosity model is illustrated with an example.

52 citations

Journal ArticleDOI
TL;DR: In this paper, porosity was calculated by a downhole resistivity log of a nearby borehole close to Munich for comparison and the attempt of transferability of the data set to other locations within the Central Molasse Basin.
Abstract: For the successful realization and productivity prediction of new hydrothermal projects in the South German Molasse Basin, the hydraulic matrix properties of the Upper Jurassic Malm reservoir have to be determined as accurately as possible. To obtain specific information on the distribution of the petrophysical parameters (e.g., rock density, porosity, and permeability) 363 samples of rare drilling cores from the reservoir northeast of Munich (wells Moosburg SC4 and Dingolfing FB) were investigated using different experimental methods. Additionally, porosity was calculated by a downhole resistivity log of a nearby borehole close to Munich for comparison and the attempt of transferability of the data set to other locations within the Central Molasse Basin. Core data were divided into groups of different stratigraphic and petrographic units to cover the heterogeneity of the carbonate aquifer and provide data ranges to improve reservoir and prediction models. Data for effective porosity show a high variance from 0.3 to 19.2% throughout this heterogeneous aquifer. Permeability measured on core samples is scattered over several orders of magnitude (10−4–102 mD). Permeability models based on the porosity–permeability relationship were used to estimate permeability for the whole aquifer section and identify possible flow zones. A newly developed empirical model based on distinct lithofacies types allows a permeability estimation with a deviation < 10 mD. However, fractured, karstified, and vuggy zones occurring in this typically karstified, fractured, and porous reservoir cannot yet be taken into account by the model and result in an underestimation of permeability on reservoir scale. Overall, the dominant permeability trends can be mapped well using this model. For the regional transfer and the correlation of the results, a core-related porosity/permeability log for the reservoir was compiled for a well close to Munich showing similarities to the core investigations. The validation of the regional transferability of the parameter set to other locations in the Molasse Basin was carried out by correlation with the interpreted log data of a well near Munich.

52 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20236
202232
202162
202065
201971
201847