Permeability changes during the flow of water through westerly granite at temperatures of 100°–400°C

Abstract

Changes in permeability have been studied during the flow of water through granite for periods of time up to 17 days at temperatures of 100°, 200°, 300°, and 400°C with a constant confining pressure of 500 bars, differential stresses of 0–3500 bars, inlet pore pressure of 275 bars, and outlet pressure of 1 bar. In all cases the initial permeability at elevated temperatures was found to be higher by 1–2 orders of magnitude than the permeability at room temperature, perhaps because of thermal stress cracking. The high initial permeability did not persist with time and in nearly all cases decreased significantly during the first ½ day of water flow. Dissolution of plagioclase and quartz was concentrated near the inlet, where the pore pressure was highest. Precipitation occurred throughout the samples because of oversaturation as the pore pressure dropped, causing significant reduction in permeability. The final permeability after 10 days was less at 300°C than at lower temperatures, and measurable flow stopped in most of the 400°C samples.

Thermal decompaction of rocks

“…More recently, the geometry of the additional pore space set up in rocks after heating has been studied with optical microscopy, scanning electron microscopy and other methods (Bauer and Johnson, 1979;Zaraisky and Balashov, 1981;Fredrich and Wong, 1986;Gerand and Gaviglio, 1990). The effect of temperature on permeability of rocks in situ and after cooling is considered in experimental studies of Zaraisky and Balashov (1978), Summers et al (1978), Morrow et al (1981), Vitovtova and Shmonov (1982), Shmonov and Vitovtova (1992), Heard and Page (1982), Nur (1982), Zonov et al (1989), and others.…”

Permeability of rocks at elevated temperatures and pressures

“…As the apparatus was set up and calibrated, a number of related investigations at elevated temperatures and pressures appeared. Notable among these are the studies on thermal decompaction of rocks to 700°C by Zaraisky and Balashov (1978) (see also Chapter 10, this volume), permeability measurements on granites, gneisses, and albites to 350°C and 50 MPa by Nikolaenko and Indutyi (1978), results on crack healing to an axial stress of 350 MPa, confining pressure of 50 MPa and temperatures of 400°C by Summers et al (1978), investigations of the permeability of limestone and sandstone in a different direction with respect to the maximum load by Marmorshtein (1981), as well as permeability measurements on granites in temperature gradient fields of up to 300°C along the sample, under a confining pressure to 60 MPa by Moore et al (1983) and Morrow et al (1981).…”

Summaries of technical reports; Volume IX, National earthquake hazards reduction program

“…However, rock strengthening can result if corrosive agents are driven off by the increase in temperature (Wu and Thomsen, 1975). In the presence of H 2 o at elevated temperature, permeability may decrease by dissolution of minerals in localized areas of high pore pressure and precipation of these in over-saturated regions of low pore pressure (Summers et al, 1978). There must also exist physical conditions at which corrosive and embrittling effects of H 2 o give way to ductile effects by facilitating the motion of slip dislocations and diffusion (Carter and Kirby, 1978).…”