Glossary

Acidization: Pressing an acid mixture (e.g. hydrochloric acid) into the uncased borehole to increase the yield by chemical reaction in the case of carbonate rock.
Aquifer: Any rock or material that yields water readily enough to be significant as a source of supply.
Carbonates: Rock, mostly created by deposition, which consist mainly of carbonate materials. They include limestone, dolomites, magnesites etc.
Cement bridge: Section of the borehole that is filled with cement and mostly serves to block off or stabilize a borehole.
Cretaceous: Age in the geological cycle (135-65 million years).
Deflexion drilling: Deflected/"steered" drillings are very complex since not only very high precision is required but they also make special demands on borehole stability.
Directional drilling (deflected/steered drilling): Directional drillings are not sunk vertically in a straight line from top to bottom but are deflected from a certain depth.
Doublet: On a geothermal doublet the thermal water is extracted from the one borehole, used for heat/energy production, and returned cooled through the other borehole.
Drilling progress: The rate at which the drill is driven forward; mostly stated in meters per hour.
Fault: Fracture in rock where there has been a displacement between the two faces (overlap or offset).
Fissure: Closed or open fracture in rock in which little movement has taken place.
Fluid loss: Penetration and loss of drilling fluid in highly permeable rock.
Fraccing (hydraulic fracturing): Method where water is pressed into rock to widen a borehole or create new fissures in the rock.
Hot-Dry-Rock (HDR) process: In order to be able to use a hot rock as a petrothermal system, the rock has to be prepared by fraccing so that it can serve as a heat exchanger. As a rule, cold water is injected as a heat transfer medium. This flows through the hot rock and the thermal energy which it contains is then brought to the surface.
Hydrothermal sources: Natural reservoirs of hot water at great depths, so-called hot water aquifers. They can be used for heat or power generation depending on temperature.
Kalina system: As with the ORC process, the Kalina system operates with a turbine with two circuits. The medium used is a mixture of water and ammonia, which already evaporates at very low temperatures.
Karst formation: Natural chemical erosion and decomposition processes in rock that can be attacked by water (e. g. limestone, dolomite, rock salt, gypsum, etc.).
Lithology (petrography): Area of science concerned with the character of rock.
Malm: Part of the Jura age in the geological cycle (163-135 million years), also known as White Jura.
Mammoth pump: Production device through which air is pumped at high pressure in the borehole and flushes up the water.
Molasse Basin: Along the northern edge of the Alps, extending from the Rhone Valley through Switzerland, Southern Germany to Austria.
ORC system (Organic Rankine Cycle): This is a turbine with two circuits (binary machine). The turbine is driven by a medium which already evaporates at low temperatures. This medium absorbs energy, e.g. from thermal water, through a heat exchanger. The thermal water does not enter the turbine.
Permeability (hydraulic conductivity): The ease with which water moves through a rock or another material.
Petrothermal systems: Rock at greater depths possesses high temperatures. If this rock is virtually water free, the energy it contains can be exploited for heat or power generation using the HDR process.
Pressing: Targeted injection of mostly fluid substances into the rock under pressure.
Re-injection: Returning the water extracted from the ground to the source of supply (for instance an aquifer).
Round trip (extending the drilling rod): When drilling to great depths the drilling rod has to be continuously extended, with new, usually alloy steel, sections.
Sedimentary rock: Rock strata created by deposition or precipitation.
Strike risk: In geothermal drillings strike risk is the risk that a geothermal reservoir cannot be tapped in sufficient quantity or quality with one (or more) drilling(s).
Triplet: A triplet consists of three, as a rule deep, drillings which are mostly deflected in different directions.
Whip-stock: Drilling aid with a sloping surface along which the drill bit is deflected into a preset direction.
Workover: When a drilling has been completed, the borehole is measured and cleaned, and pumping and production tests are carried out to determine the hydrothermal and hydraulic characteristics.