Geologic and geophysical data for wells drilled at Raft River Valley, Cassia County, Idaho, in 1977-1978 and data for wells drilled previously

In order to better define the size of the thermal anomaly in the Raft River Valley, Idaho, the U.S. Geological Survey drilled a series of intermediate-depth (nominal 500-ft depth) wells in 1977 and 1978.  This report presents geologic, geophysical, and temperature data for these drill holes, along with data for five wells drilled by the Idaho National Engineering Laboratory with U.S. Department of Energy Funding.  Data previously reported for other drill holes are also included in order to make them available as digital files.

For purposes of defining the thermal anomaly for the geothermal system, temperature gradients are calculated over long depth intervals on the basis of the appearance of reasonable linear segments on a temperature versus plot depth.  Temperature versus depth data for some drill holes can be represented by a single gradient, whereas others require multiple gradients to match the data.  Data for some drill holes clearly reflect vertical flows of water in the formation surrounding the drill holes, and water velocities are calculated for these drill holes.  Within The Narrows area, temperature versus depth data show reversals at different depth in different drill holes.  In the main thermal area, temperatures in intermediate-depth drill holes vary approximately linearly but with very high values of temperature gradient.  Temperature gradients on a map of the area can be reasonable divided into a large area of regional gradients and smaller areas defining the thermal anomalies.