Borehole induced structures in image logs of wells from the Coso Geothermal Field (CGF), CA record variation in the azimuth of principal stress. Image logs of these structures from five wells were analyzed to quantify the stress heterogeneity for three geologically distinct locations: two wells within the CGF (one in an actively produced volume), two on the margin of the CGF and outside the production area, and a control well several tens of kilometers south of the CGF. Average directions of Shmin and its standard deviation are similar along the eastern portion of the geothermal field at ~106±28°, but this is distinct from the western portion which has an azimuth of 081±18° and distinct from outside the geothermal field where the average azimuth is 092±47°. Spectral analysis was applied to the depth variation of stress direction and demonstrates that: (1) the data set contains distinct wavelengths of stress rotation, (2) that the relative power of these wavelengths in the total distribution of stress directions is fractally distributed and (3) in a manner consistent with earthquakes causing the stress rotations. The slope of the power spectrum quantifies the length-scale dependence of stress rotations for the volume of the brittle crust penetrated by each well. While the vertically averaged Shmin orientation for the three eastern wells inside the field varied by as little as 1˚, the spectral slopes inside the field varied by 0.4 log(deg2*m)(m), from the inside to the margin unproduced areas of the CGF.

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