Combined Structural Analysis of Core and Image Log of Well 76-31 East of Mt Baker, Washington State

Despite active volcanism, few geothermal energy resources have been developed in the Cascades region of the Pacific Northwest. Washington Geological Survey, in partnership with AltaRock Energy, Cyrq Energy, the Department of Energy, the U.S. Geological Survey, and Temple University have been searching for zones where fractures provide fluid conduits that transport deep volcanic heat to shallow depths and could supply the state with carbon neutral energy. Guided by a Play Fairway assessment (PFA) of resource potential, a temperature core hole was drilled in 2019 at Little Park Creek, 11 km west-southwest of the summit of Mount Baker Volcano. Rock core, repeat temperature logs, and a geophysical image log were obtained to ~440 m depth to probe for heat and fluid flow in fracture systems. The core was mapped by hand on acetate, digitized and then correlated with the image and temperature logs. The core analysis reveals complex, steeply dipping networks of fractures and brecciation along slickensided strike slip faults. The majority of fractures are thoroughly healed by layers of chlorite and calcite; preservation of pyrite indicates anoxic conditions. The combination of complex, non-planar fracture zones and healing promote misinterpretation of natural fracture attitude and density in the image log. The healing and anoxic conditions are consistent with the conductive temperature gradient measured in the well below a shallow isothermal zone, although, several fractures are open and resulted in fluid entries into the well. The equilibrated measured temperature gradient of 64ºC/km and calculated heat flow of 145 mW/m^2 is more than twice the regional average, indicating local influence of the Mt Baker magmatic system at the Little Park Creek TCH site. Further analysis of the PFA geophysical and geological data sets is ongoing in order to identify additional exploratory drilling sites.