TY - GEN
T1 - The effect of inhomogeneous surface relaxivity on nuclear magnetic resonance relaxation rates
AU - Keating, Kristina
PY - 2010/1/1
Y1 - 2010/1/1
N2 - Proton nuclear magnetic resonance relaxation (NMR) relaxation rates can be used in geophysics to estimate the pore-size distribution and permeability of water saturated geologic material. The interpretation of NMR data to this end relies on the assumption that the surface relaxivity, an important NMR parameter, is uniform and constant in the measured volume. However, when more than one mineral type is present in a measured volume, the surface relaxivity can be inhomogeneous. This laboratory study was designed to explore the effect of inhomogeneous surface relaxivity on NMR relaxation rates. NMR measurements were collected on water saturated mixtures of quartz sand coated with the iron hydroxide mineral ferrihydrite (Fe(OH)3 H2O). The iron-coated quartz sand was mixed with pure quartz sand at seven concentrations: 1%, 2%, 5%, 10%, 25%, 50%, and 75%. NMR measurements were also collected on samples containing pure quartz sand and 100% iron-coated sand. Four NMR relaxation rates (mean log, bulk fluid, diffusion and surface relaxation rates) were calculated from the NMR data. The surface relaxation rates and measured surface areas were used to calculate the average surface relaxivity of each sample and to estimate the surface relaxivity corresponding to the iron-coated sand in each sample. The surface relaxivity corresponding to the iron-coated sand was then compared with the known surface relaxivity for the iron-coated sand determined from the 100% iron-coated sand sample. For samples with iron-coated sand concentrations 25% the ironcoated sand surface relaxivity was constant with concentration. For the samples with iron-coated sand concentrations <25% the surface relaxivity was not constant with concentration. We conclude that the relationship between the surface relaxivity and the relaxation rate depends on the concentration of ironcoated sand.
AB - Proton nuclear magnetic resonance relaxation (NMR) relaxation rates can be used in geophysics to estimate the pore-size distribution and permeability of water saturated geologic material. The interpretation of NMR data to this end relies on the assumption that the surface relaxivity, an important NMR parameter, is uniform and constant in the measured volume. However, when more than one mineral type is present in a measured volume, the surface relaxivity can be inhomogeneous. This laboratory study was designed to explore the effect of inhomogeneous surface relaxivity on NMR relaxation rates. NMR measurements were collected on water saturated mixtures of quartz sand coated with the iron hydroxide mineral ferrihydrite (Fe(OH)3 H2O). The iron-coated quartz sand was mixed with pure quartz sand at seven concentrations: 1%, 2%, 5%, 10%, 25%, 50%, and 75%. NMR measurements were also collected on samples containing pure quartz sand and 100% iron-coated sand. Four NMR relaxation rates (mean log, bulk fluid, diffusion and surface relaxation rates) were calculated from the NMR data. The surface relaxation rates and measured surface areas were used to calculate the average surface relaxivity of each sample and to estimate the surface relaxivity corresponding to the iron-coated sand in each sample. The surface relaxivity corresponding to the iron-coated sand was then compared with the known surface relaxivity for the iron-coated sand determined from the 100% iron-coated sand sample. For samples with iron-coated sand concentrations 25% the ironcoated sand surface relaxivity was constant with concentration. For the samples with iron-coated sand concentrations <25% the surface relaxivity was not constant with concentration. We conclude that the relationship between the surface relaxivity and the relaxation rate depends on the concentration of ironcoated sand.
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U2 - 10.1190/1.3513674
DO - 10.1190/1.3513674
M3 - Conference contribution
SN - 9781617389801
T3 - Society of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010
SP - 3946
EP - 3950
BT - Society of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010
PB - Society of Exploration Geophysicists
T2 - Society of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010
Y2 - 17 October 2010 through 22 October 2010
ER -