Analysis of macroscopic fractures in the Cajon Pass Scientific Drillhole: Over the interval 1829-2115 meters



The orientation, distribution and apparent aperture of natural fractures intersecting the Cajon Pass research well were determined through analysis of borehole televiewer (BHTV) data over the interval 1829 to 2115 meters. Large open fractures have shallow inclinations and tend to be aligned striking roughly N15°E. There is no apparent relationship between these fractures and the current stress state, as measured by the analysis of wellbore breakouts and hydraulic fracturing experiments in the Cajon Pass well and as observed in other studies in the region. Temperature anomalies due to fluid flow into the well detected during a long-term permeability experiment occur at several of these fractures. Compressional, shear and Stoneley guided wave velocities are within the expected range for crystalline rocks and elastic-wave anomalies are associated with the larger fractures. Stoneley wave coherence is reduced where the fractures are hydraulically conductive.