Experimental Permeability Studies at Elevated Temperature and Pressure of Granitic Rocks.

摘要

Permeability of quartz monzonite from the Los Alamos hot-dry-rock geothermal well GT-2was experimentally measured as a function of pressure and temperature. Permeability of the GT-2rocks from depths of 8580ft and 9522ft behaves like Westerly granite for changes in effective confining pressure. However,permeability of these rocks behaves much differently with increasing temperature. As temperature is increased,the permeability of Westerly granite passes through a slight minimum and then increases exponentially above 100exp 0 C. Upon cooling the permeability shows a permanent increase of up to four times its original value. The permeability of GT-2-9522',on the other hand,drops off exponentially with increasing temperature,reaching a minimum near 140exp 0 C;above 150exp 0 C,permeability rises slowly. These changes in permeability with temperature are postulated to be caused by differential thermal expansion (DTE), a phenomena related to the anisotropic and inhomogeneous coefficients of thermal expansion of the mineral grains in the rock. Scanning electron photomicrographs of unheated and heated samples of Westerly and GT-2rocks support the DTE hypothesis. Differences in the behavior of these rocks with temperature are believed to be due to the respective temperature and pressure environments in which they became equilibrated,since both GT-2rocks had existed at moderately high temperatures and pressures for some time. Temperature disequilibrium of the GT-2rocks in their present in situ environments is believed to have caused the differences in the behavior between the two samples and may provide a method for determining the pre-intrusion geothermal gradient of the Jemez area. Flow channels were observed in GT-2samples using radioactive tracer techniques. Several radioactive isotopes were tried in these experiments,including exp 22Na,exp 63Ni,and exp 35 S. (ERA citation 03:049857)