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Title: Pore Space Connectivity and the Transport Properties of Rocks

Abstract

Pore connectivity is likely one of the most important factors affecting the permeability of reservoir rocks. Furthermore, connectivity effects are not restricted to materials approaching a percolation transition but can continuously and gradually occur in rocks undergoing geological processes such as mechanical and chemical diagenesis. Here, we compiled sets of published measurements of porosity, permeability and formation factor, performed in samples of unconsolidated granular aggregates, in which connectivity does not change, and in two other materials, sintered glass beads and Fontainebleau sandstone, in which connectivity does change. We compared these data to the predictions of a Kozeny-Carman model of permeability, which does not account for variations in connectivity, and to those of Bernabé et al. (2010, 2011) model, which does [Bernabé Y., Li M., Maineult A. (2010) Permeability and pore connectivity: a new model based on network simulations, J. Geophys. Res. 115, B10203; Bernabé Y., Zamora M., Li M., Maineult A., Tang Y.B. (2011) Pore connectivity, permeability and electrical formation factor: a new model and comparison to experimental data, J. Geophys. Res. 116, B11204]. Both models agreed equally well with experimental data obtained in unconsolidated granular media. But, in the other materials, especially in the low porosity samples that hadmore » undergone the greatest amount of sintering or diagenesis, only Bernabé et al. model matched the experimental data satisfactorily. In comparison, predictions of the Kozeny-Carman model differed by orders of magnitude. The advantage of the Bernabé et al. model was its ability to account for a continuous, gradual reduction in pore connectivity during sintering or diagenesis. Though we can only speculate at this juncture about the mechanisms responsible for the connectivity reduction, we propose two possible mechanisms, likely to be active at different stages of sintering and diagenesis, and thus allowing the gradual evolution observed experimentally.« less

Authors:
 [1];  [2];  [2];  [1]
  1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Earth Atmospheric and Planetary Sciences Dept.
  2. Southwest Petroleum Univ., Chengdu (China). State Key Lab. of Oil and Gas Reservoir Geology and Exploitation
Publication Date:
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1395332
Grant/Contract Number:
FG09-97ER14760; FG02-97ER14760
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Oil and Gas Science and Technology
Additional Journal Information:
Journal Volume: 71; Journal Issue: 4; Journal ID: ISSN 1294-4475
Publisher:
IFPEN
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES

Citation Formats

Bernabé, Yves, Li, Min, Tang, Yan-Bing, and Evans, Brian. Pore Space Connectivity and the Transport Properties of Rocks. United States: N. p., 2016. Web. doi:10.2516/ogst/2015037.
Bernabé, Yves, Li, Min, Tang, Yan-Bing, & Evans, Brian. Pore Space Connectivity and the Transport Properties of Rocks. United States. doi:10.2516/ogst/2015037.
Bernabé, Yves, Li, Min, Tang, Yan-Bing, and Evans, Brian. 2016. "Pore Space Connectivity and the Transport Properties of Rocks". United States. doi:10.2516/ogst/2015037. https://www.osti.gov/servlets/purl/1395332.
@article{osti_1395332,
title = {Pore Space Connectivity and the Transport Properties of Rocks},
author = {Bernabé, Yves and Li, Min and Tang, Yan-Bing and Evans, Brian},
abstractNote = {Pore connectivity is likely one of the most important factors affecting the permeability of reservoir rocks. Furthermore, connectivity effects are not restricted to materials approaching a percolation transition but can continuously and gradually occur in rocks undergoing geological processes such as mechanical and chemical diagenesis. Here, we compiled sets of published measurements of porosity, permeability and formation factor, performed in samples of unconsolidated granular aggregates, in which connectivity does not change, and in two other materials, sintered glass beads and Fontainebleau sandstone, in which connectivity does change. We compared these data to the predictions of a Kozeny-Carman model of permeability, which does not account for variations in connectivity, and to those of Bernabé et al. (2010, 2011) model, which does [Bernabé Y., Li M., Maineult A. (2010) Permeability and pore connectivity: a new model based on network simulations, J. Geophys. Res. 115, B10203; Bernabé Y., Zamora M., Li M., Maineult A., Tang Y.B. (2011) Pore connectivity, permeability and electrical formation factor: a new model and comparison to experimental data, J. Geophys. Res. 116, B11204]. Both models agreed equally well with experimental data obtained in unconsolidated granular media. But, in the other materials, especially in the low porosity samples that had undergone the greatest amount of sintering or diagenesis, only Bernabé et al. model matched the experimental data satisfactorily. In comparison, predictions of the Kozeny-Carman model differed by orders of magnitude. The advantage of the Bernabé et al. model was its ability to account for a continuous, gradual reduction in pore connectivity during sintering or diagenesis. Though we can only speculate at this juncture about the mechanisms responsible for the connectivity reduction, we propose two possible mechanisms, likely to be active at different stages of sintering and diagenesis, and thus allowing the gradual evolution observed experimentally.},
doi = {10.2516/ogst/2015037},
journal = {Oil and Gas Science and Technology},
number = 4,
volume = 71,
place = {United States},
year = 2016,
month = 6
}

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  • The authors construct model systems to study pore scale conductivity, by making the models from an array of spheres, tubes, and cracks with different dimensions. They vary the conductivity of this system by changing the sizes and distributions of the different pore elements. To determine the transport properties of this model system, they equated the sum of the energy lost at each pore junction, to the total energy lost in the array, for either fluid or electrical conduction through the array. The authors argue that this model conduction system should be applicable to study conductivity through rock, and allow onemore » to learn more about transport properties of rock.« less
  • Petrographic and electron-microscopic study of Tertiary clays and argillaceous rocks lifted from deep drillholes of Azerbaidzhan reveals their porometric characteristics. It is established that these rocks are incompletely consolidated and it is inferred that there is a connection between such a structure or pore space in argillaceous rocks and the development in them of abnormally high pressures of pore fluids, and that these factors affect the screening off properties of argillaceous seals, the mechanism of folding, clay diapirism and earthquakes.
  • Retardation of nuclear contaminants in rock matrices can lead to long retention times, allowing substantial radionuclide decay prior to eventual release. Imbibition and diffusion into the rock matrix can move contaminants away from an active fracture, thereby contributing to their retardation. However, diffusive transport in some rocks may behave anomalously because of their sparsely connected porespace, in contrast to diffusion in rocks with denser pore connections. We examined imbibition of weakly sorbing tracers into welded tuff and Indiana sandstone, and water imbibition into metagraywacke and Berea sandstone. Tuff samples were initially equilibrated to 12% and 76% water (v/v) within controlledmore » humidity chambers, while the other rocks were air-dried. For imbibition, one face was exposed to water, with or without tracer, and uptake was measured over time. Following imbibition, tracer concentration measurements were made at fine (1 mm) increments. Three anomalous results were observed: (1) Indiana sandstone and metagraywacke showed mass of imbibed water scaling as time{sup 0.26}, while tuff and Berea sandstone showed the more classical scaling with time{sup 0.5}; (2) tracer movement into dry (2% initial saturation) Indiana sandstone showed a dispersion pattern similar to that expected during tracer movement into moist (76% initial saturation) tuff; and (3) tracer concentrations at the inlet face of the tuff sample were approximately twice those deeper inside the sample. The experiment was then modeled using random walk methods on a 3-D lattice with different values of pore coordination. Network model simulations that used a pore coordination of 1.49 for Indiana sandstone and 1.56 for metagraywacke showed similar temporal scaling, a result of their porespace being close to the percolation threshold. Tracer concentration profiles in Indiana sandstone and tuff were closely matched by simulations that used pore coordinations of 1.49 and 1.68, respectively, because of how low connectivity alters the accessible porosity in the vicinity of the inlet face. The study supports pore connectivity as a coherent explanation for the observed anomalies and demonstrates the utility of pore-scale modeling in elucidating mechanisms critical to radionuclide retardation in geological repositories.« less
  • Retardation of nuclear contaminants in rock matrices can lead to long retention times, allowing substantial radionuclide decay prior to eventual release. Imbibition and diffusion into the rock matrix can move contaminants away from an active fracture, thereby contributing to their retardation. However, diffusive transport in some rocks may behave anomalously because of their sparsely connected porespace, in contrast to diffusion in rocks with denser pore connections. We examined imbibition of weakly sorbing tracers into welded tuff and Indiana sandstone, and water imbibition into metagraywacke and Berea sandstone. Tuff samples were initially equilibrated to 12% and 76% water (v/v) within controlledmore » humidity chambers, while the other rocks were air-dried. For imbibition, one face was exposed to water, with or without tracer, and uptake was measured over time. Following imbibition, tracer concentration measurements were made at fine (1 mm) increments. Three anomalous results were observed: (1) Indiana sandstone and metagraywacke showed mass of imbibed water scaling as time{sup 0.26}, while tuff and Berea sandstone showed the more classical scaling with time{sup 0.05}; (2) tracer movement into dry (2% initial saturation) Indiana sandstone showed a dispersion pattern similar to that expected during tracer movement into moist (76% initial saturation) tuft and (3) tracer concentrations at the inlet face of the tuff sample were approximately twice those deeper inside the sample. The experiment was then modeled using random walk methods on a 3-D lattice with different values of pore coordination. Network model simulations that used a pore coordination of 1.49 for Indiana sandstone and 1.56 for metagraywacke showed similar temporal scaling, a result of their porespace being close to the percolation threshold. Tracer concentration profiles in Indiana sandstone and tuff were closely matched by simulations that used pore coordinations of 1.49 and 1.68, respectively, because of how low connectivity alters the accessible porosity in the vicinity of the inlet face. The study supports pore connectivity as a coherent explanation for the observed anomalies and demonstrates the utility of pore-scale modeling in elucidating mechanisms critical to radionuclide retardation in geological repositories.« less
  • The permeability, capillary properties, and m values of carbonate rocks are related to the particle size, amount of interparticle porosity, amount of separate vug porosity, and the presence or absence of touching vugs. Particle size, percent separate vug porosity, and the presence or absence of touching vugs usually can be determined visually. The amount of interparticle porosity is more difficult to determine visually and is done best by subtracting the visual estimate of separate vug porosity from the measure of total porosity obtained from wireline porosity logs or laboratory measurements. In the absence of touching vugs, the permeability, m values,more » and capillary properties can be estimated if the particle size, percent separate vug porosity, and total porosity are known. No acceptable method has been developed to estimate visually the permeability of touching vugs. A classification of carbonate porosity is proposed based on the data presented. This classification is intended to be used in the field or for routine laboratory description. Interparticle porosity is classified according to particle size and the dense or porous appearance of the interparticle area. Vuggy porosity is classified according to type of interconnection. Separate vugs are connected through the interparticle pore space and classified by percent porosity. Touching vugs are connected to each other and classified by presence or absence.« less