ASTM E957-03(2011)e1

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Designation: E957 − 03 (Reapproved 2011)
Standard Terminology Relating to
Geothermal Energy
This standard is issued under the fixed designation E957; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—Typographical errors were corrected editorially in September 2011.
aquifer, n—a water-bearing, permeable body of rock or granu- geothermal energy, n—the thermal energy contained in the
lar material below the surface of the earth. rocks and fluids of the earth.
binary cycle plant, n—a facility that generates electric power geothermal facility,n—thephysicalcomponentsnecessaryfor
by transferring heat from produced geothermal fluids to a the utilization of geothermal energy, including the reservoir,
non-aqueous working fluid that vaporizes and causes a production and injection wells, pipelines, and the power
turbine to rotate the shaft of a generator. plant or direct-use facility.
brine,n—ingeothermal,fluidsinaliquidphasethathavebeen
geothermal fluid, n—water in a vapor or liquid phase or in a
producedfromgeothermalwellsorfromhotspringsandthat mixtureofthesephasesthatexistswithinorhasbeenemitted
contain appreciable amounts of sodium chloride and other
from a geothermal reservoir, together with any entrained or
salts. dissolved substances.
capacity, n—the power which a component of a geothermal geothermal gradient, n—the change in temperature of the
facility (e.g., a well, a reservoir, a power plant, or a
earth with depth, expressed either in degrees of temperature
direct-use facility) is capable of supplying at a point in time, per unit depth, or units of depth per degree.
assuming that other required components of the geothermal
geothermal power plant, n—a facility for the production of
facilityareavailable.Capacityisexpressedinunitsofpower
electricity using geothermal energy, typically including a
(e.g., Megawatts, kilowatts).
turbine, a generator, and associated surface equipment.
direct-use facility, n—a facility which uses geothermal energy
geothermal heat pump, n—a heat pump that transfers energy
for purposes other than the generation of electricity (e.g.,
to or from the earth.
space heating, greenhouses, bathing, and industrial pro-
cesses).
geothermal reserves, n—the amount of energy anticipated to
beeconomicallyrecoverablefromageothermalfacilityover
fumarole, n—a vent at the earth’s surface that emits steam or
a specified time period (e.g., the project life) using existing
gaseous vapor.
technology. Geothermal reserves are expressed in units of
DISCUSSION—Such vents are usually found in volcanic areas.
energy (e.g., terajoules in SI units), which are dimensionally
geochemistry, n—the study of the chemistry of the rocks and
equivalenttounitsofpowermultipliedbyunitsoftime(e.g.,
fluids of the earth for the purpose of understanding their
Megawatt-years or kilowatt-hours). Geothermal reserves
composition, their temperature, and their origin.
may also be expressed as an equivalent amount of another
energy source (e.g., barrels of oil equivalent).
geothermal, adj—relating to or derived from the natural heat
DISCUSSION—Geothermal reserves can also be characterized as to the
of the earth.
degree of certainty of recovery. By analogy to usage in the mining and
petroleum industries, reserves may be qualified as proven, probable, or
geothermal anomaly, n—a conspicuous deviation of the
possible.
earth’s temperature, geothermal gradient, or heat flow from
Example of Usage:
average values; an area where such a deviation exists.
This facility has geothermal reserves of 4,000 Megawatt-
years, recoverable over a project life of 30 years.
This terminology is under the jurisdiction of ASTM Committee E44 on Solar,
geothermal reservoir, n—an aquifer of sufficient temperature
GeothermalandOtherAlternativeEnergySourcesandisthedirectresponsibilityof
and permeability to support the economic use of geothermal
Subcommittee E44.01 on Terminology and Editorial.
energy.
Current edition approved Sept. 1, 2011. Published September 2011. Originally
DISCUSSION—The extent of a geothermal reservoir is determined by
approved in 1983. Last previous edition approved in 2003 as E957–03. DOI:
10.1520/E0957-03R11E01. the degree of hydrologic interconnection. When an aquifer contains
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E957 − 03 (2011)
bothhotportionsandportionsthataretoocoolforeconomicuse,those
porosity, n—the ratio of the aggregate volume of interstices in
portions that are sufficiently interconnected to have a significant
a rock or soil to its total volume, usually stated as a percent.
hydrologic or thermal impact on each other are considered part of the
same geothermal reservoir.
project life, n—the time period over which the economic
viability of a geothermal facility is evaluated.
geothermal steam, n—a geothermal fluid in the vapor phase.
reinjection/injection, n—theprocessofconveyinggeothermal
geothermometer, n—a method of estimating the temperature
fluids to sub-surface formations through wells.
of a geothermal reservoir based on the minerals in the
DISCUSSION—After such fluids have been processed by a geothermal
reservoir rock or the concentration of chemical species in
power plant or its associated facilities, or both, this process is
geothermal fluids that have come from the reservoir.
sometimes referred to as “reinjection” when injected water circulates
back through the geothermal reservoir to the production wells.
geyser, n—a spring that intermittently blows forth hot water
and steam.
steam purity, n—the proportion by mass of pure vapor-and
liquid-phase water in a fluid mixture that consists primarily
heat flow, n—dissipation or transfer of heat coming from
of steam.
withintheearthbyconduction,convectionorradiationatthe
DISCUSSION—Geothermal steam may contain impurities, such as
surface; usually reported in units of energy per unit time per
silica, sodium, chloride, iron and solid particulates. Steam purity
unitarea,forexample,joulespersecondpersquaremetreor
expresses the proportion by mass of pure water (in both liquid and
watts per square metre.
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