Rocky Mountain Section - 72nd Annual Meeting - 2020

Paper No. 18-4
Presentation Time: 8:30 AM-4:30 PM


SMITH, Connor J., LACHMAR, Thomas E., SHERVAIS, John W., EVANS, James P. and NEWELL, Dennis L., Department of Geosciences, Utah State University, 4505 Old Main Hill, Logan, UT 84322-4505

Recent exploration for geothermal resources in the Snake River Plain (SRP) used a Play Fairway Analysis (PFA) approach. PFA integrates geophysical, geological, and geochemical data into a statistical framework to locate regions with high geothermal potential. The three parameters indicating geothermal potential reviewed in this assessment were heat source, permeable reservoir, and a cap or seal. The PFA revealed an area in the Camas Prairie (CP), ID exhibiting favorability in these three parameters. High heat flow, the presence of relatively young volcanic vents, warm springs, and anomalously high helium isotopic signatures in water samples suggest that the CP has a magmatic heat source. Complex fault systems documented by potential field geophysics and seismic surveys imply zones of high permeability at depth. The presence of a clay seal overlying one zone of complex fault intersections is indicated by magnetotelluric data. To validate this geothermal assessment, the CP was selected for drilling.

An exploration borehole was advanced using rotary methods to ~1,608’ (490 m) below ground surface (bgs) in October 2018. In the fall of 2019, the hole was extended and cored to a total depth of ~2,028.5’ (618 m) bgs.

The maximum groundwater temperature measured was ~80o C at ~1,200 ft (366 m) bgs. The artesian flow rate calculated in July was ~11 gpm. Soon thereafter the head declined to a level below the surface. A permeable zone was encountered at a depth of ~1,160 feet (354 m) with inflow of hot water. The transmissivity of the permeable zone was ~4 Darcy-meters. Water samples collected under artesian conditions exhibit lower values of δ18O and δ2H than local waters sampled at higher elevations in the Mount Bennet Hills. This shows that the groundwater is influenced by meteoric waters and is consistent with local trends in δ18O and δ2H established by spring and well samples tested previously. Based on these data, as well as the temperatures and depths of other wells in the vicinity, it appears as if the geothermal fluids may rise from depth at a yet unknown location and then flow horizontally at relatively shallow depths.