Shear-wave splitting of acoustic emissions (AE) was analyzed to obtain a description and evaluation of subsurface cracks in a natural geothermal reservoir. During shutdown operations of production wells in 1984-1986 at the Kakkonda (Takinoue) geothermal power plant, Japan, several thousand AE events were located with a downhole tri-axial AE sonde. A total of 145 of these events showed shear-wave splitting and they were used to estimate depth and crack density of multiple layers in the reservoir. The shear-wave polarization was used to determine the orientation of the cracks, and crack density was calculated from delays between shear-wave polarization-anomalies. The reservoir was divided into three zones based on observed characteristics of the shear wave splitting. These zones are identified as the injection, production and intermediate zones.
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