2012-395

The Impact of Surface Charge on the Mechanical Behavior 3 of High-Porosity Chalk

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Title:The Impact of Surface Charge on the Mechanical Behavior 3 of High-Porosity Chalk

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Articles (Tidsskriftartikler)
Authors:Megawati, M.
Hiorth, A.
Madland, M.V.
Research group:Økt utvinning (Improved Oil Recovery)
Distribution restriction:Open
Published by:Springer Vienna, http://rd.springer.com/journal/603
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Additional information:
Rock Mechanics and Rock Engineering, ISSN: 0723-2632 (Print)1434-453X (Online), DOI 10.1007/s00603-012-0317-z 2012;Published by: Springer Vienna, http://rd.springer.com/journal/603;

Abstract:
We present rock mechanical test results and analytical calculations which ;demonstrate that a negative surface charge, resulting from sulfate adsorption ;from the pore water, impacts the rock mechanical behavior of high-porosity ;chalk. Na2SO4 brine flooded into chalk cores at 130 °C results in significantly ;reduced bulk modulus and yield point compared with that of NaCl brine at the ;same conditions. The experimental results have been interpreted using a surface ;complexation model combined with the Gouy-Chapman theory to describe the double ;layer. The calculated sulfate adsorption agrees well with the measured data. A ;sulfate adsorption of about 0.3 μmol/m2 and 0.7–1 μmol/m2 was measured at 50 ;and 130 °C, respectively. Relative to a total sites of 5 sites/nm2 these values ;correspond to an occupation of 4 % and 8–13 % which sufficiently explains the ;negative charging of the calcite surfaces. The interaction between charged ;surfaces specifically in the weak overlaps of electrical double layer gives ;rise to the total disjoining pressure in granular contacts. The net repulsive ;forces act as normal forces in the grains vicinity, counteracting the cohesive ;forces and enhance pore collapse failure during isotropic loading, which we ;argue to account for the reduced yield and bulk modulus of chalk cores. The ;effect of disjoining pressure is also assessed at different sulfate ;concentrations in aqueous solution, temperatures, as well as ionic strength of ;solution; all together remarkably reproduce similar trends as observed in the ;mechanical properties.;;;;;;;;;;;;;

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International Research Institute of Stavanger
Mailing address:
Visiting address:
P.O. Box 8046, N-4068 Stavanger, Norway
Prof. Olav Hanssensvei 15, 4021 Stavanger


Phone:
Fax:

+47 51 87 50 00
+47 51 87 52 00

General email address: firmapost@iris.no