skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Carbon-enhanced electrical conductivity during fracture of rocks

Abstract

Changes in electrical resistance during rock fracture in the presence of a carbonaceous atmosphere have been investigated using Nugget sandstone and Westerly granite. The experiments were performed in an internally heated, gas-pressure vessel with a load train that produced strain rates between 10{sup {minus}6} and 10{sup {minus}5}; s{sup {minus}1}. Samples were deformed at temperatures of 354{degree} to 502; {degree}C and pressures of 100 to 170 MPa in atmospheres of Ar or mixtures of 95{percent} CO{sub 2} with 5{percent} CO or 5{percent} CH{sub 4}, compositions that are well within the field of graphite stability at the run conditions. In experiments using Nugget sandstone, resistance reached a minimum value when the maximum temperature was achieved and good electrode contact was made. The resistance then increased as the experiment continued, probably due to dry out of the sample, a change in the oxidation state of the Fe-oxide associated with the cement, or destruction of current-bearing pathways. At approximately 200-MPa end load, the rock sample failed. Plots of load and resistance versus time show several interesting features. In one experiment, for example, as the end load reached about 175 MPa, resistance stopped increasing and remained fairly constant for a period of approximately 0.5 hour.more » During loading, the end load displayed small decreases that were simultaneous with small decreases in resistance; when the end load (and the displacement) indicated rock failure, resistance decreased dramatically, from {approximately}150 M{Omega} to 100 M{Omega}. In a single experiment, the Westerly granite also showed a decrease in resistance during dilatancy. The nature and distribution of carbon in the run products were studied by electron microprobe and time-of-flight secondary-ion mass spectroscopy (TOF-SIMS). Carbon observed by mapping with the former is clearly observed on microcracks that, based on the microtexture, are interpreted to have formed during the deformation. The TOF-SIMS data confirm the electron-probe observations that carbon is present on fracture surfaces. These observations and experimental results lead to the hypothesis that as microfractures open in the time leading up to failure along a fracture, carbon is deposited as a continuous film on the new, reactive mineral surfaces, and this produces a decrease in resistance. Subsequent changes in resistance occur as connectivity of the initial fracture network is altered by continued deformation. Such a process may explain some electromagnetic effects associated with earthquakes. {copyright} 1999 American Geophysical Union« less

Authors:
;  [1]; ;  [2];  [3]
  1. Geosciences and Global Security Program, Lawrence Livermore National Laboratory, Livermore, California (United States)
  2. Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York (United States)
  3. Earth and Environmental Science Division, Los Alamos National Laboratory, Los Alamos, New Mexico (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
OSTI Identifier:
328583
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Journal Article
Journal Name:
Journal of Geophysical Research
Additional Journal Information:
Journal Volume: 104; Journal Issue: B1; Other Information: PBD: Jan 1999
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; ELECTRIC CONDUCTIVITY; CARBON COMPOUNDS; OXYGEN COMPOUNDS; HYDROGEN COMPOUNDS; ROCKS; FRACTURE PROPERTIES; EARTHQUAKES; GEOLOGIC FAULTS; STRAIN RATE; CARBON DIOXIDE; CARBON MONOXIDE; METHANE; GEOCHEMISTRY; EARTH CRUST; TIME DEPENDENCE; TEMPERATURE RANGE 0400-1000 K; VERY HIGH PRESSURE

Citation Formats

Roberts, J J, Duba, A G, Mathez, E A, Kinzler, R, and Shankland, T J. Carbon-enhanced electrical conductivity during fracture of rocks. United States: N. p., 1999. Web. doi:10.1029/1998JB900032.
Roberts, J J, Duba, A G, Mathez, E A, Kinzler, R, & Shankland, T J. Carbon-enhanced electrical conductivity during fracture of rocks. United States. https://doi.org/10.1029/1998JB900032
Roberts, J J, Duba, A G, Mathez, E A, Kinzler, R, and Shankland, T J. Fri . "Carbon-enhanced electrical conductivity during fracture of rocks". United States. https://doi.org/10.1029/1998JB900032.
@article{osti_328583,
title = {Carbon-enhanced electrical conductivity during fracture of rocks},
author = {Roberts, J J and Duba, A G and Mathez, E A and Kinzler, R and Shankland, T J},
abstractNote = {Changes in electrical resistance during rock fracture in the presence of a carbonaceous atmosphere have been investigated using Nugget sandstone and Westerly granite. The experiments were performed in an internally heated, gas-pressure vessel with a load train that produced strain rates between 10{sup {minus}6} and 10{sup {minus}5}; s{sup {minus}1}. Samples were deformed at temperatures of 354{degree} to 502; {degree}C and pressures of 100 to 170 MPa in atmospheres of Ar or mixtures of 95{percent} CO{sub 2} with 5{percent} CO or 5{percent} CH{sub 4}, compositions that are well within the field of graphite stability at the run conditions. In experiments using Nugget sandstone, resistance reached a minimum value when the maximum temperature was achieved and good electrode contact was made. The resistance then increased as the experiment continued, probably due to dry out of the sample, a change in the oxidation state of the Fe-oxide associated with the cement, or destruction of current-bearing pathways. At approximately 200-MPa end load, the rock sample failed. Plots of load and resistance versus time show several interesting features. In one experiment, for example, as the end load reached about 175 MPa, resistance stopped increasing and remained fairly constant for a period of approximately 0.5 hour. During loading, the end load displayed small decreases that were simultaneous with small decreases in resistance; when the end load (and the displacement) indicated rock failure, resistance decreased dramatically, from {approximately}150 M{Omega} to 100 M{Omega}. In a single experiment, the Westerly granite also showed a decrease in resistance during dilatancy. The nature and distribution of carbon in the run products were studied by electron microprobe and time-of-flight secondary-ion mass spectroscopy (TOF-SIMS). Carbon observed by mapping with the former is clearly observed on microcracks that, based on the microtexture, are interpreted to have formed during the deformation. The TOF-SIMS data confirm the electron-probe observations that carbon is present on fracture surfaces. These observations and experimental results lead to the hypothesis that as microfractures open in the time leading up to failure along a fracture, carbon is deposited as a continuous film on the new, reactive mineral surfaces, and this produces a decrease in resistance. Subsequent changes in resistance occur as connectivity of the initial fracture network is altered by continued deformation. Such a process may explain some electromagnetic effects associated with earthquakes. {copyright} 1999 American Geophysical Union},
doi = {10.1029/1998JB900032},
url = {https://www.osti.gov/biblio/328583}, journal = {Journal of Geophysical Research},
number = B1,
volume = 104,
place = {United States},
year = {1999},
month = {1}
}