A unit of volume. A U.S. gallon has 231 cubic inches or 3.785 liters. There are 42 gallons in a barrel of oil.

That state of matter which has neither independent shape nor volume. Gas expands to fill the entire container in which it is held. Gas is one of the three forms of matter: solid, liquid and gas.

Gas conditioning
The removal of objectionable constituents and addition of desirable constituents.

Gas field
A field containing natural gas, but no oil.

Gas governor station (see pressure regulating station)
Equipment installed for the purpose of automatically reducing and regulating the pressure in the downstream pipeline or main to which it is connected. Included are piping auxiliary devices such as valves, control instruments, control lines, the enclosures, and ventilating equipment.

Gas hydrates
A solid ice-like material resulting from the combination of a gas with water under pressure. Of natural gas constituents – methane, ethane, propane, isobutane, normal butane, and also hydrogen sulfide and carbon dioxide will form hydrates. The greater the pressure in the equipment, the higher the temperature at which the hydrate will form, usually well above freezing. Hydrates can cause restriction or stoppage of flow, and can be controlled by alcohol injection or by dehydration of the gas. Methane hydrates are found in some permafrost regions and beneath portions of the ocean floor and may eventually be a source of methane gas.

Gas transmission line
Pipeline transporting natural gas from principal supply areas to distribution centers, large volume customers or other transmission lines. Transmission lines generally have a linear configuration, may be quite large in diameter, operate at relatively high pressure, and traverse long distances.

Gaseous effluent
Gaseous waste from an economic processing or production structure (plant, waste treatment station, etc. ), which is a potential source of pollution harmful to the environment.

A process that exposes a solid fuel to heat in the presence of limited oxygen to produce a gaseous fuel. This fuel contains hydrogen but also other gases such as carbon monoxide, carbon dioxide, nitrogen, and methane. Under suitable circumstances, gasification can produce synthesis gas, a mixture of just hydrogen and carbon monoxide.

A liquid petroleum distillate having a viscosity intermediate between that of kerosene and lubricating oil. It derives its name from having originally been used in the manufacture of illuminating gas. It is now used to produce distillate fuel oils and gasoline.

A complex mixture of relatively volatile hydrocarbons, with or without additives, which have been blended to form a fuel suitable for use in internal combustion engines.

A machine that converts mechanical energy into electrical energy. Generally rated in terms of real power (megawatts) and reactive power (Megavars) output or in terms or real power output (megawatts) and power factor. Generators require a source of mechanical energy input (typically a turbine) and ancillary equipment to interface with the transmission network.

The study of the chemical composition of the earth’s crust and the changes which takes place within it.

Geographical Information System (GIS)
A computer system for capturing, checking, integrating, analyzing and displaying data related to positions on the earth’s surface. Typically, a Geographical Information System (or Spatial Information System) is used for handling maps of one kind or another. These might be represented as several different layers where each layer holds data about a particular kind of feature. Each feature is linked to a position on the graphical image of a map. Layers of data are organised to be studied and to perform statistical analysis.

Geologic map
A map showing the type and spatial distribution of rocks at the surface of the Earth. Rock formations are color-coded and symbols for geological structures are annotated, so age relationships are evident. Topographic contours and cultural features can also appear on geologic maps.

The science that deals with the study of the planet Earth, the materials of which it is made, the processes that act to change these materials from one form to another, and the history recorded by these materials; the forces acting to deform the outer layers of the Earth and create ocean basins and continents; the processes that modify the Earth’s surface; the application of geologic knowledge to the search for useful materials and the understanding of the relationship of geologic processes to people.

An essentially impermeable membrane used with soil, earth, rock and foundation as a requisite part of an engineered project. As thermoplastic solid sheet material it’s intended to block the passage of ground water. Geotextile, Textile made from synthetic fibers, usually nonbiodegradable. Geotextiles can be woven or nonwoven and have varying degrees of porosity. They are used as moisture barriers, for separation or reinforcement of soils, for filtration, and for drainage.

A device used in surface seismic acquisition, both onshore and on the seabed offshore, that detects ground velocity produced by seismic waves and transforms the motion into electrical impulses. Geophones detect motion in only one direction. Conventional seismic surveys on land use one geophone per receiver location to detect motion in the vertical direction. Three mutually orthogonal geophones are typically used in combination to collect 3C seismic data. Hydrophones, unlike geophones, detect changes in pressure rather than motion.

Geophysics is the study of Earth physics including the fields of meteorology, hydrology, oceanography, seismology, volcanology, magnetism, radioactivity and geodesy.

The application of scientific methods and engineering principles to the acquisition, interpretation and use of knowledge of materials of the Earth’s crust for the solution of engineering problems.

Geothermal energy
Energy from the internal heat of the Earth, which may be residual heat, friction heat, or a result of radioactive decay. The heat is found in rocks and fluids at various depths, and can be extracted by drilling and/or pumping.

Geothermal gradient
The rate of increase of temperature in the Earth with depth. The gradient near the surface of the Earth varies from place to place, depending on the heat flow in the region and on the thermal conductivity of the rock. Approximate average geothermal gradient in the Earth’s crust is about 25ºC/km.

A thermal spring that intermittently erupts steam and boiling water.

Giant’s kettle
In physical geography, the name applied to cavities or holes which appear to have been drilled in the surrounding rocks by eddying currents of water bearing stones, gravel and other detrital matter. The size varies from a few inches to several feet in depth and diameter. The commonest occurrence is in regions where glaciers exist or have existed; a famous locality is the Gletscher Garten of Lucerne, where there are 32 giant’s kettles, the largest being 26 ft. wide and 30 ft. deep; they are also common in Germany, Norway and in the United States. It appears that water, produced by the thawing of the ice and snow, forms streams on the surface of the glacier, which, having gathered into their courses a certain amount of morainic debris, are finally cast down a crevasse as a swirling cascade or moulin.

Respiratory organ of many aquatic animals; a filamentous outgrowth well supplied with blood vessels at which gas exchange between water and blood occurs.

(see Geographical Information System)

A moving body of ice that forms on land from the accumulation and compaction of snow, and that flows downslope or outward due to gravity and the pressure of its own weight.

(see Alcohols and Glicohols).

Global climate change
Gradual changing of global climates due to the buildup of carbon dioxide and other greenhouse gases in the earth’s atmosphere. Carbon dioxide produced by burning fossil fuels has reached levels greater than what can be absorbed by green plants and the seas.

Global Positioning System (GPS)
A technology that uses signals and data from multiple satellites to determine a location anywhere on Earth.

Sweet, syrupy alcohol that is naturally produced from vegetable oils, or produced synthetically from propylene alcohol. It is used in cosmetics as a solvent, plasticizer, emollient, and lubricant.

A narrow or deep ravine or canyon.

(see Global Positioning System).

The determination of the different grain size in a granular material.

Gravimeter, gravity meter
A highly sensitive weighing instrument that is used to measure variations in the magnitude of a gravitational field or the specific gravity of a substance.

Gravimetric surveys
A survey made to determine the acceleration of gravity at various places on the Earth’s surface.

The measurement, correction, mapping, and interpretation of the earth’s gravitational field by surface or borehole measurements.

Gravitational field
The area influenced by an object’s gravity.

Gravitational force
The attractive force between all masses in the universe. All objects that have mass possess a gravitational force that attracts all other masses. The more massive the object, the stronger the gravitational force. The closer objects are to each other, the stronger the gravitational attraction.

Greenhouse effect
The presence of trace atmospheric gases make the earth warmer than would direct sunlight alone. These gases (carbon dioxide [CO2], methane [CH4], nitrous oxide [N2O], tropospheric ozone [O3], and water vapor [H2O]) allow visible light and ultraviolet light (shortwave radiation) to pass through the atmosphere and heat the earth’s surface. This heat is re-radiated from the earth in form of infrared energy (longwave radiation). The greenhouse gases absorb part of that energy before it escapes into space. This process of trapping the longwave radiation is known as the greenhouse effect. In itself, the greenhouse effect is essential to the existence of life on earth. The phenomenon which represents an environmental problem is the accentuation of the natural greenhouse effect caused by certain atmospheric gases – referred to as greenhouse gases (see) – which prevent the escape of heat from the earth.

Greenhouse gases
Greenhouse gases cause and accelerate the greenhouse effect (see). Key gases are carbon dioxide (produced by combustion) and methane (often produced by anaerobic digestion such as occurs in landfill sites, and from the guts of cattle and termites), but also Nitrous Oxide (N2O) in vehicle exhaust fumes, PFCs (perfluorocarbons), SF6 (sulphur hexafluoride) and HFC (hydrofluorocarbons) in refrigerants.

Greenpeace is a non-profit organisation, with a presence in 40 countries across Europe, the Americas, Asia and the Pacific. Founded in Canada in 1971, it relies on contributions from individual supporters and foundation grants. As a global organisation, Greenpeace focuses on the most critical worldwide environmental issues such as: – Oceans and ancient forests protection; – Fossil fuel phase out and the promotion of renewable energies to stop climate change; – Nuclear disarmament and an end to nuclear contamination; – Elimination of toxic chemicals; – Preventing the release of genetically engineered organisms into nature.

Ground storage tanks
The storage of certain hazardous substances, above-ground or underground, presents a potential threat to public health and the environment (see groundwater).

Freshwater beneath the earth’s surface (usually in aquifers) supplying wells and springs. Because groundwater is a major source of drinking water, there is a growing concern over leaching of agricultural and industrial pollutants or substances from underground storage tanks (see).

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