Low pore connectivity in natural rock.

As repositories for CO(2) and radioactive waste, as oil and gas reservoirs, and as contaminated sites needing remediation, rock formations play a central role in energy and environmental management. The connectivity of the rock's porespace strongly affects fluid flow and solute transport. This work examines pore connectivity and its implications for fluid flow and chemical transport. Three experimental approaches (imbibition, tracer concentration profiles, and imaging) were used in combination with network modeling. In the imbibition results, three types of imbibition slope [log (cumulative imbibition) vs. log (imbibition time)] were found: the classical 0.5, plus 0.26, and 0.26 transitioning to 0.5. The imbibition slope of 0.26 seen in Indiana sandstone, metagraywacke, and Barnett shale indicates low pore connectivity, in contrast to the slope of 0.5 seen in the well-connected Berea sandstone. In the tracer profile work, rocks exhibited different distances to the plateau porosity, consistent with the pore connectivity from the imbibition tests. Injection of a molten metal into connected pore spaces, followed by 2-D imaging of the solidified alloy in polished thin sections, allowed direct assessment of pore structure and lateral connection in the rock samples. Pore-scale network modeling gave results consistent with measurements, confirming pore connectivity as the underlying cause of both anomalous behaviors: imbibition slope not having the classical value of 0.5, and accessible porosity being a function of distance from the edge. A poorly connected porespace will exhibit anomalous behavior in fluid flow and chemical transport, such as a lower imbibition slope (in air-water system) and diffusion rate than expected from classical behavior.

[1]  J. Bear.  Dynamics of Fluids in Porous Media , 1975 .

[2]  Marcel G. Schaap,et al.  Percolation Theory for Flow in Porous Media , 2006 .

[3]  Yves Guéguen,et al.  Percolation networks and fluid transport in the crust , 1991 .

[4]  R. R. Bruce,et al.  The Measurement of Soil Moisture Diffusivity 1 , 1956 .

[5]  Peter Persoff,et al.  Laboratory measurement of water imbibition into low-permeability welded tuff , 2001 .

[6]  Gary Mavko,et al.  The effect of a percolation threshold in the Kozeny‐Carman relation , 1997 .

[7]  John King Vennard,et al.  Elementary Fluid Mechanics , 1940 .

[8]  Joanne T. Fredrich,et al.  Predicting macroscopic transport properties using microscopic image data , 2005 .

[9]  Allen G. Hunt,et al.  Percolative transport in fractal porous media , 2004 .

[10]  Seungoh Ryu,et al.  Determining multiple length scales in rocks , 2000, Nature.

[11]  J. Kaufmann.  Characterization of Pore Space of Cement‐Based Materials by Combined Mercury and Wood's Metal Intrusion , 2009 .

[12]  Peter Persoff,et al.  Hydrologic characterization of reservoir metagraywacke from shallow and deep levels of The Geysers vapor-dominated geothermal system, California, USA , 2001 .

[13]  J. Philip,et al.  THE THEORY OF INFILTRATION: 4. SORPTIVITY AND ALGEBRAIC INFILTRATION EQUATIONS , 1957 .

[14]  R. Ewing,et al.  Scale dependence of intragranular porosity, tortuosity, and diffusivity , 2010 .

[15]  J. Philip,et al.  The Theory of Infiltration , 1958 .

[16]  T. Reuschlé,et al.  Direct Assessment of Wood’s Metal Wettability on Quartz , 1999 .

[17]  R. Horton,et al.  Diffusion in sparsely connected pore spaces: Temporal and spatial scaling , 2002 .

[18]  S. Dultz,et al.  DETERMINATION OF POROSITY AND PORE CONNECTIVITY IN FELDSPARS FROM SOILS OF GRANITE AND SAPROLITE , 2006 .

[19]  R. Sigal,et al.  Examination of the Importance of Self Diffusion in the Transportation of Gas in Shale Gas Reservoirs , 2008 .

[20]  Ivars Neretnieks,et al.  Diffusion in the rock matrix: An important factor in radionuclide retardation? , 1980 .

[21]  S. Redner,et al.  Introduction To Percolation Theory , 2018 .

[22]  K. Bowker.  Barnett Shale gas production, Fort Worth Basin: Issues and discussion , 2007 .

[23]  Wilkinson,et al.  Transport and dispersion in random networks with percolation disorder. , 1988, Physical review. A, General physics.

[24]  A. Hildenbrand,et al.  Investigation of the morphology of pore space in mudstones—first results , 2003 .

[25]  E. W. Washburn.  Note on a Method of Determining the Distribution of Pore Sizes in a Porous Material. , 1921, Proceedings of the National Academy of Sciences of the United States of America.

[26]  F. Dullien,et al.  Wood's metal porosimetry and its relation to mercury porosimetry , 1981 .

[27]  B. F. Swanson.  Visualizing Pores and Nonwetting Phase in Porous Rock , 1979 .

[28]  A. Möri,et al.  Radionuclide transport in fractured granite interface zones , 2007 .

[29]  Timothy J Kneafsey,et al.  Tracer Penetration into Welded Tuff Matrix from Flowing Fractures , 2002 .

[30]  J. Kaufmann.  Pore space analysis of cement-based materials by combined Nitrogen sorption – Wood’s metal impregnation and multi-cycle mercury intrusion , 2010 .

[31]  M. Sahini,et al.  Applications of Percolation Theory , 2023, Applied Mathematical Sciences.

[32]  T. Madden,et al.  Microcrack connectivity in rocks: A renormalization group approach to the critical phenomena of conduction and failure in crystalline rocks , 1983 .

[33]  Wilkinson,et al.  Percolation effects in immiscible displacement. , 1986, Physical review. A, General physics.

[34]  Alexis Maineult,et al.  Permeability and pore connectivity: A new model based on network simulations , 2010 .

[35]  D. Boutt,et al.  Systematic diagenetic changes in the grain-scale morphology and permeability of a quartz-cemented quartz arenite , 2011 .