Adularia Hydrothermal potassium bearing feldspar that forms in volcanic hosted geothermal reservoirs and is a favorable indicator of boiling and permeable conditions.

Aquifer Porous and permeable rock unit or unconsolidated layer in the subsurface in which all the pores and voids are filled with water. Water supply for wells comes from aquifers.

Basalt Dark grey fine grained volcanic rock composed of plagioclase, pyroxene and olivine, with relatively low silica (45-52 wt %). The composition reflects an upper mantle origin. Basalt is the most common type of volcanic rock on Earth, and it erupts from mid-ocean...

BHA Refers to Bottom Hole Assembly, which is the system of tools at the bottom of the drill string that is used for drilling directional wells. The BHA includes the drill bit, mud motor, drill collar, and any tools that are used for making measurements while...

Binary Cycle Power Plant A power plant in which the produced geothermal fluid passes through a heat exchanger and heats a low boiling point liquid, commonly an organic compound such as pentane, to vaporize and condense as it passes through a turbine and generate...

Breccia Angular to sub-angular fragments of broken rock that are cemented together that are highly permeable and form on the surface due to sedimentary or igneous processes or in fault zones.

Brine In producing geothermal fields, this term refers to the hot water that is produced from wells. It is rarely as salty as implied. Instead, the salinities of most natural hot waters are commonly less than seawater, but they contain a wide range of rock-forming...

Cap Rock A poorly permeable or impermeable layer that overlies a geothermal reservoir. The term is borrowed from the oil industry and was once considered an essential feature of a producing geothermal resource in confining the flow and pressure of hot water....

Casing Shoe In geothermal wells, this is the bottom of the cemented casing string. Below the casing shoe, the well may be unprotected and open to the surrounding rock or lined with a slotted liner. The depth of the casing shoe generally coincides with the top of the...

Cement Bond Log A geophysical well log that is obtained using a sonic-type tool on a wireline. The result helps to confirm the integrity of the hardened cement that was injected to form a bond between well casing and the adjacent rock formation.

Chemical Geothermometer A temperature that is calculated based on the chemical composition of a hydrothermal fluid and involves knowing a ratio (e.g., Na/K) or knowing the absolute concentration of a species (e.g., SiO2). Temperature is computed using a simple...

Chlorite A micaceous mineral that is commonly green-colored, composed of iron and/or magnesium, and forms due to hydrothermal alteration of amphiboles, pyroxenes, and feldspars.