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Glossary

Dam
A structure of earth, rock, or concrete designed to form a basin and hold water back to make a pond, lake, or reservoir. A barrier built, usually across a watercourse, for impounding or diverting the flow of water. General types of dams include: [1] Arch Dam—The arch curves toward the flow of water, and the main water load is distributed along the dam to the sidewalls of the narrow Valley or canyon in which some dams are built. [2] Buttress Dam—Has an upstream face or deck to support the impounded water, and a series of buttresses or triangular vertical walls built to support the deck and transmit the water load to the foundation. [3] Cofferdam—A temporary watertight enclosure that is pumped dry to expose the bottom of a body of water so that construction, as of piers, a dam, and bridge footings, may be undertaken. A “diversion cofferdam” prevents all downstream flow by diverting the flow of a river into a pipe, channel, or tunnel. [4] Crib Dam—A barrier or form of Gravity Dam constructed of timber forming bays, boxes, cribs, crossed timbers, gabions or cells that are filled with earth, stone or heavy material. [5] Embankment Dam—A dam structure constructed of fill material, usually earth or rock, placed with sloping sides and usually with a length greater than its height [6] Gravity Dam—Solid concrete structures with triangular cross sections; the dam is thick at the base and thinner toward the top. When viewed from above, they are either straight or only slightly curved; the upstream face is nearly vertical. [7] Masonry Dam—A dam constructed mainly of stone, brick, or concrete blocks that may or may not be joined with mortar. A dam having only a masonry facing should not be referred to as a masonry dam. [8] Weir—A dam in a river to stop and raise the water, for the purpose of conducting it to a mill, forming a fishpond, or the like. When uncontrolled, the weir is termed a fixed-crest weir. Other types of weirs include broad-crested, sharp-crested, drowned, and submerged. A dam across a water channel for diverting of for measuring the flow of water.

Deballasting
The discharging of unwanted water (see ballast) from the vessel in order to: free tanks to receive cargo; raise vessel out of water sufficiently to enable loading to begin.

Decarburization
The removal of carbon from the surface of steel as a result of heating in a medium that reacts with the carbon. Decarburization is usually present to a slight extent in steel forgings. Excessive decarburization can result in defective products.

Decibel (DB)
A tenth of a bel. A unit used to measure the volume of a sound, equal to ten times the common logarithm of the ratio of the intensity of the sound to the intensity of an arbitrarily chosen standard sound. The decibel also is used to measure relative strengths of antenna and amplified signals and always refers to a ratio or difference between two values.

Decommissioning
Activity that takes place after deactivation and includes surveillance and maintenance, decontamination, and/or dismantlement. These actions are taken to retire a facility from service while protecting workers, the public, and the environment.

Decomposer
Organisms that convert dead organic material into simpler forms that can be used as plant nutrients (bacteria and fungi).

Decomposition
The biochemical process where biological materials are broken down into smaller particles and eventually into basic chemical compounds and elements. See also decomposer.

Decompression
Decompression is the removal of pressure. (see Pressure regulating station)

Deforestation
Clearing of tree formations and their replacement by non-forest land uses.

Degradation
The breakdown of complex organic structures to simpler compounds by the influence of bacteria,usually accelerated by oxygen and sunlight.

Demersal
Organism living at or near the sea floor but having the capacity for active swimming.

Denitrification system
The anoxic (without oxygen) biological conversion of nitrate to nitrogen gas. It occurs naturally in surface waters low in oxygen, and it can be engineered in wastewater treatment systems.

Density
Matter measured as mass per unit volume expressed in pounds per gallon (lb/gal), pounds per cubic foot (lb/ft3), and kilograms per cubic meter (kg/m3). The mass of quantity of a substance per unit volume. (2) (Biology) The number per unit area of individuals of any given species at any given time. A term used synonymously with Population Density.

Densmore Amos, Hatch Charles P.
Charles P. Hatch of the Empire Transportation Company invented the rail tank car in 1865. It was a flat car with wooden banded tubes mounted on top, capable of carrying 3,500 gallons of crude oil on the Oil Creek and Warren and Franklin Railroads in Pennsylvania. Another inventor, Amos Densmore, built similar cars around the same time for the Atlantic & Great Western Railroad.

Denudation
Erosion by rain, frost, wind or water of the solid matter of the earth. The often implies the removal of soil down to the bedrock; removal, by natural or artificial means, of all vegetation and organic matter.” Source: United Nations, Glossary of Environment Statistics

Department Of Energy (DOE)
A federal government agency created in 1977, that is entrusted to contribute to the welfare of the United States by providing technical information, and a scientific and educational foundation for technology, policy and institutional leadership to achieve efficiency in energy use, diversity in energy sources, a more productive and competitive economy, improved environmental quality, and a secure national defense.

Depleted batteries
Lead-acid batteries should not be disposed of in landfill sites. Lead in batteries is present in a soluble form and can contaminate soil and water. Automotive lead-acid batteries can be recycled; the lead is re-refined and used to make more batteries and the plastic is recycled into more plastic casings for the batteries.

Depth of water table
Vertical distance between a point on the ground surface and the surface of the uppermost groundwater storey.

Derrick
Load-bearing towerlike framework over an oil/gas well which holds the hoisting and lowering equipment.

Desalinization
To remove salts and other chemicals, as from sea water or soil, for example. Usually used with respect to the salt contained in water. Also referred to as Desalting.

Desert
An area where evaporation exceeds precipitation, for whatever reason, with consequent lack of vegetation. Evaporation rates will vary, according to temperature, but less than 25 centimeters of rain annually will produce a desert in almost any temperature range.

Desertification
The transformation of arable or habitable land to desert, as by a change in climate or destructive land use. The term is generally applied to the production of artificial deserts where people have intensified the problems caused by droughts through overgrazing marginal land, repeated burning of natural vegetation, intensive farming of arid land, aggressive removal of trees, and prolonged irrigation of arid land for agricultural use.

Desulphurisation and hydrodesulphurisation
A process by which petroleum fractions are treated in order to reduce the content of sulphur in petroleum products. Treatment takes place in high-pressure and high-temperature plant in the presence of catalyst and hydrogen.

Detritivore
Organism that obtains most of its nutrients form debris of organic substances of vegetable or animal origin. Detritus, the dead organic matter, such as fallen leaves, twigs, and other plant and animal wastes, that exist in any ecosystem

Diagenesis
All of the changes that occur to a fossil (or more generally any sediment) after initial burial; includes changes that result from chemical, physical as well as biological processes. The study of diagenesis is part of taphonomy.

Dicotiledon
A subdivision of flowering plants whose members possess two embryonic seed leaves, or cotyledons.

Diesel engine
An internal combustion engine in which air is compressed to a temperature sufficiently high to ignite fuel injected into the cylinder where the combustion actuates a piston.

Diesel oil
Fuel for diesel engines obtained from the distillation of petroleum. It is composed chiefly of aliphatic hydrocarbons. Its volatility is similar to that of gas oil. Its efficiency is measured by cetane number.

Digester
Tank in which sludge is placed to allow decomposition by microorganisms. Digestion (see) may occur under anaerobic (most common) or aerobic conditions.

Digestion
The biochemical decomposition of organic matter, resulting in partial gasification, liquefaction, and mineralization of pollutants. In wastewater treatment, the biological decomposition of organic matter in sludge.

Dike
An embankment to confine or control water, and/or soil.

Dioxin
Any of a family of compounds known chemically as dibenzo-p-dioxins. Concern about them arises from their potential toxicity and contaminants in commercial products. Tests on laboratory animals indicate that it is one of the more toxic man-made chemicals known.

Directional drilling
The technique of drilling at an angle from the vertical by deflecting the drill bit. Directional wells are often drilled to reach an oil- or gas-bearing reservoir where drilling cannot be done, such as beneath a shipping lane in the ocean. Directional drilling is being used increasingly to intersect reservoirs at angles that exposes more of the rock to the wellbore and increases the amount of oil or gas that flows into the well.

Dispatching
A call for action to effectuate a transaction. For example, a request to the operator for a certain amount of gas to be delivered. Also, the resulting sendout of natural gas. More generally, the control of product flow in a system involving the assignment of load to the various sources of supply.

Distillation
The first step in the refining process. During distillation, crude oil is heated in the base of a distillation tower. As the temperature increases, the crude’s various compounds vaporize in succession at their various boiling points, then rise to prescribed levels within the tower according to their densities, condense in distillation trays, and are drawn off individually for further refining. Distillation is also used at other points in the refining process to remove impurities. (see Refining)

DOE
(see department of energy)

Dose
A specified quantity of a therapeutic agent, such as a drug or medicine, prescribed to be taken at one time or at stated intervals.

Downstream
The oil industry term used to refer to all petroleum activities from the processing of refining crude oil into petroleum products to the distribution, marketing, and shipping of the products. The opposite of downstream is upstream (see).

Drainage
Act, process or means of removing excess water from the surface.

Draining-off or drawdown
Lowering of the ground water surface or the piezometric pressure caused by pumping, measured as the difference between the original ground-water level and the current pumping level after a period of pumping.

Drake, Edwin
American oil industry pioneer. President (from 1858) of the Seneca Oil Company, he was the first to obtain oil from beneath the surface of the earth by drilling (1859, Titusville, PA).

Drill string
String of individual joints of pipe that extends from the bit to the kelly and carries the mud down to, and rotates, the bit.

Drilling
The process of boring deep into the earth’s crust to access underground liquid resources such as oil and water.

Drilling muds
A mixture of clays, water and chemicals pumped in and out of the well bore during drilling. Drilling mud provides circulation, flushing rock cuttings from the bottom of the well bore to the surface. It maintains pressure at the bottom of the well bore and cakes the uncased well bore wall to provide some protection against cave-ins.

Drilling platform
An offshore platform used to drill exploration and development wells but lacking the processing facilities of a production platform (see). The structure with legs is anchored to the sea bottom that supports the drilling of up to 35 wells from one location. Production platform A platform from which development wells are drilled and that carries all the associated processing plants and other equipment needed to maintain a field in production.

Drillship
A maritime vessel modified to include a drilling rig and special station-keeping equipment. The vessel is typically capable of operating in deep water. A drillship must stay relatively stationary on location in the water for extended periods of time.

Drought
A condition that occurs when precipitation is less than normal and the water going out of the reservoirs exceeds the flow coming in. The prolonged absence or marked deficiency of precipitation in some regions may contribute to desertification (see).

Dynamic positioning
The stationing of a vessel, especially a drillship (see) or semisubmersible drilling rig, at a specific location in the sea by the use of computer-controlled propulsion units called thrusters. Though drilling vessels have varying sea and weather state design conditions, most remain relatively stable even under high wind, wave and current loading conditions. Inability to maintain station keeping, whether due to excessive natural forces or failure of one or more electromechanical systems, leads to a “drive off” condition that requires emergency procedures.

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