Helium Isotopes Helium gas is a trace constituent of groundwater and thermal fluids, and the ratio of 3He to 4He can be measured with a high-precision mass spectrometer to determine whether...

Hot Dry Rock Hot crystalline rock with essentially no porosity and lacking producible hot water. Geothermal production from hot dry rock reservoirs is the primary goal of EGS (enhanced...

Hydraulic Fracture A rock-hosted tensile fracture that is created by injection of fluid under high pressure.