ＡＳＲ法による岩手県湯ノ森地域の三次元地圧計測

Abstract

The ASR (Anelastic Strain Recovery) method for measuring three-dimensional in-situ stresses, which had been developed by one of the authors, was successfully applied at Yunomori geothermal field, Japan for seven cores collected from the depths of up to about 1, 500m of two wells. The rocks were tuffs, a shale and an andesite. Temperatures of the cores were from 100 to 210°Cbefore drilling. From the data of anelastic normal strains measured with strain gauges in six independent directions, both principal stress directions and the ratios of principal stress deviations were determined without knowing the anelastic strain recovery characteristics of the rocks. The results were consistent with the orientation of the maximum principal stress estimated from borehole breakouts observed in the wells and also consistent with the direction of the maximum horizontal compression observed by surface survey. Furthermore, for one of the cores, magnitudes of principal stresses were determined by calibrating the anelastic strain recovery compliances of both shear and volumetric modes in the laboratory under the conditions of drained triaxial compression. The results were compared with those obtained by DSCA and the combined AE and DRA methods carried out by NEDO. The results of the ASR method were consistent with those of DSCA.