The effects of water fluid at temperatures up to 850°C and pressure of 300 MPa on porosity and permeability of amphibolite

Details The effects of water fluid at temperatures up to 850°C and pressure of 300 MPa on porosity and permeability of amphibolite The effects of water fluid at temperatures up to 850°C and pressure of 300 MPa on porosity and permeability of amphibolite

Mar 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993pepi...76..219z&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 76, Issue 3-4, p. 219-227.

Physics

4

Scientific paper

Compressional wave velocities were measured in amphibolite under gas and water fluid pressure of 300 MPa and at temperatures up to 850°C. Fluid and confining pressures were equal during the experiments. The data obtained under water pressure differ from those for gas pressure by the reversion of the Vp temperature trend: on heating under gas pressure Vp decreases throughout the temperature range, whereas on heating under water pressure Vp decreases at first, reaches a minimum value at approximately 650°C and then increases. A similar Vp trend was determined for quenched samples. For initial and quenched amphibolite samples, porosity, permeability and pore size distribution were measured and the microstructure was examined. It was found that changes in the elastic properties of rock with temperature rise are determined by the transformation of its microstructure. The temperature trends of porosity and permeability are in negative correlation with the Vp temperature trends. The increase of effective porosity is caused by initiation of new microcracks and the opening of pre-existing microcracks. The decrease of effective porosity is caused by the sealing of microcracks (mostly thin ones). Two types of processes are responsible for the transformation of pore structure: phase transitions within a narrow temperature range (the high-low quartz transition at T ~ 650°C, P = 300 MPa, and the partial melting of amphibolite at T = 740-760°C, P = 300 MPa) and processes that take place throughout the temperature range. These latter processes are caused by thermal stress accumulation and relaxation. Under gas pressure, thermally induced microcracking leads to porosity increase and Vp decrease. Under water pressure, the processes of microcrack generation and sealing develop simultaneously. At temperatures below 650°C the processes leading to microcrack generation and porosity increase prevail and, as a result, Vp decreases. At temperatures over 650°C the processes leading to microcrack sealing and porosity decrease prevail, with a concomitant Vp increase.

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