Glossary - Letter C

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Calorific Value

The amount of heat released by the complete combustion of a fuel, expressed in kilowatt-hours (kWh) or in megajoules (MJ) per cubic meter.

Cap Rock

An impermeable barrier that blocks the migration of oil and gas to the surface.

Carbon Dioxide (CO₂)

Along with water vapor, carbon dioxide is the primary greenhouse gas (GHG) in the Earth's atmosphere. Given the huge amounts emitted into the atmosphere by humans since the Industrial Revolution, this gas is the leading cause of global warming.

Carbon Footprint

The carbon footprint (also known as greenhouse gas inventory) of a good or service measures the impact human activities have on the environment using the total greenhouse gas emissions generated during the product's life cycle, from extracting the raw materials right up to end-of-life recycling or disposal.

Carbon Monoxide

Carbon monoxide is a carbon oxide with a chemical formula of CO. It is produced by the partial oxidation of carbon-containing compounds, especially in equipment whose fuel lacks sufficient oxygen, such as boilers, furnaces and defective water heaters. It is an extremely toxic gas, made more dangerous by the fact that it is odorless and colorless, and has a density similar to nitrogen. In industry, carbon monoxide is one of two essential components of syngas (see definition), hydrogen being the other.

Carbon Sink

Natural reservoir that captures carbon dioxide and traps it via a chemical or biochemical reactions, helping to reduce overall concentrations of CO2 in the atmosphere. Carbon sinks also include artificial reservoirs used to store CO2. The main carbon sinks are oceans, new-growth forests and soils such as peat lands, permafrost and humus. Coal, oil and natural gas deposits, seabed methane hydrates and certain rocks, such as carbonates, are also carbon sinks and are all associated with very long-term sedimentary processes.


A well bore is inherently unstable due to the pressure gradient between the formations being drilled through and the hole through which the drilling fluid flows, and to the circulation of this fluid in the hole. To prevent the well bore from collapsing, which could result in the drill string becoming stuck or even abandonment of the borehole, steel cylinders called casings are lowered downhole section by section and screwed together in the same way as drill pipes. Once inserted, the entire length of each casing is cemented to the rock formation to ensure it remains stable. Each casing has a smaller diameter than the previous one.

Catalytic Cracking

Process in which heavier hydrocarbons are converted into lighter products at high temperature (around 500°C) using a catalyst.

Catalytic Reforming

Catalytic reforming is a refining process used to convert a large portion of the natural naphtha hydrocarbons in oil into the high-octane aromatic hydrocarbons needed in fuel. The process is carried out in high-temperature (500 - 550°C), high pressure reactors in the presence of a platinum catalyst.

Cellulosic Ethanol

A biofuel produced from plant-derived waste such as straw or wood pulp. It is just as efficient as “standard” ethanol, but is more environmentally friendly to manufacture because it reuses otherwise unusable waste.

Chain Reaction

The nuclei of uranium-235 atoms are bombarded by neutrons in order to induce a nuclear fission reaction. Some of these nuclei split into two smaller nuclei, releasing heat and radiation. This radiation contains other neutrons that can then bombard other atoms, which are in turn undergo fission. This process is known as a chain reaction. In nuclear power plants, this chain reaction is fully controlled. In a nuclear weapon, the concentration of fissile material is significantly higher to achieve the critical mass required to trigger the chain reaction spontaneously and release colossal amounts of energy in a few fractions of a second.


Charcoal is carbon produced by the pyrolysis of wood in the absence of oxygen. Made in kilns, where the wood was stacked under a layer of clay, until the 19th century, charcoal is now produced in modern furnaces.

Chemical Stimulation

Use of a fluid to improve the permeability of a reservoir that contains a network of natural or artificial fractures. Hydrochloric acid can be used to dissolve carbonates or hydrofluoric acid to dissolve silicon found along cracks and fractures. Chemical stimulation and acid fracturing are often used together.


A city in Ukraine where a nuclear disaster occurred in 1986, causing loss of life, major property damage and severe threats to the local population and environment for decades to come.

Chlorofluorocarbon (CFC)/Hydrochlorofluorocarbon (HCFC)

CFC is a compound consisting of carbon, chlorine and fluorine; HCFC is a compound consisting of carbon, chlorine, fluorine and hydrogen. They are gaseous at ambient temperature and pressure and were used not so long ago as coolants in air conditioning units and as propellants in aerosol sprays. They deplete stratospheric ozone, thereby contributing to the greenhouse effect. Their manufacture and use are banned.

Civil Nuclear Fission

The use of nuclear fission to generate power. The atom that undergoes fission is the naturally unstable and fissile isotope uranium U235, which is present in small quantities in natural uranium. The natural fission reaction — splitting of the nucleus into two smaller nuclei — is accelerated in the reactor using a nuclear fuel enriched with U235. This reaction releases heat, radiation and neutrons that in turn cause nearby atoms to split, in what is known as a chain reaction. The intense heat released is used to generate power.


See Carbon Dioxide


Coal is ranked by its degree of transformation or maturity, increasing in carbon content from lignite to sub-bituminous to bituminous to anthracite.

Coal Seam

Term for a coal bed in a sedimentary series.


The simultaneous production of both heat (thermal energy) and power (produced by harnessing mechanical energy) in the same facility. Also know as combined heat and power (CHP).


Coke is a coal derivative obtained through pyrolysis. It consists of almost pure carbon and is used in the steel industry to manufacture cast iron and steel.

Coker Unit

Unit with multiple, parallel 8-meter-high furnaces (heaters) used for the fast production of large quantities of coke from coal.


Coking is a thermal process (pyrolysis at about 1000°C in the case of coal) used to turn coal and heavy residuals (bottoms) from crude oil distillation into coke. The coking process also enables useful by-products such as methane, benzol and coal tar to be recovered.

Compact Fluorescent Lamp

A low-energy light bulb that uses five times less energy than a standard incandescent light bulb to produce the same intensity of light. It has a service life that is eight to ten times longer. These lamps contain mercury, a hazardous substance, in powder and vapor form. This means that they must be disposed of at a special collection point.

Concentrated Photovoltaic Panel

Panel that concentrates sunlight on solar cells using lenses or mirrors. These systems have a high energy output, but are complex and expensive because they require the use of heliostats and cooling systems.

Concession Contract

Oil contract under which the producing State receives fixed royalties that are calculated according to the amount of oil produced, irrespective of the price at which the oil is sold. The oil company owns the production and sets the production rate. This type of contract, weighted heavily in favor of oil companies, is rarely used today.


Condensate is a type of very light oil that comes from natural gas deposits. When the extracted gas's pressure and temperature drop, especially when exposed to atmospheric conditions on the surface, a fraction of the gas condenses into liquid. Hence the name condensate. The amount can vary widely depending on the deposit.


A consortium is an association of individuals, companies, organizations, governments or any combination thereof temporarily collaborating on a program or project with the aim of achieving a defined objective by pooling financial, material and human resources.

Conversion (Refining)

In energy, conversion is the transformation of one type of energy to another. For example, an internal combustion engine converts the chemical energy of fuel into mechanical energy, which enables a vehicle to move.
In refining, conversion refers to the transformation of the petroleum fractions not widely used in the industry, usually heavy distillates, to fractions with properties in high demand, such as lighter distillates. The main conversion processes are catalytic reforming, catalytic cracking, hydrocracking, alkylation and isomerization.

Cooling Water System

A reactor in a nuclear power plant has three major systems: the primary, secondary and cooling water systems. The cooling water system uses either cold water from the sea or a river or cooling towers to condense the steam from the secondary system as it leaves the turbines.


The "Conferences of Parties" (COP) bring together every year since 1995 196 States + the European Union that have signed the United Nations Framework Convention on Climate Change (UNFCCC). Cities, companies and civil society associations also take part in the meetings.

Core (Nuclear Reactor)

The part of the nuclear reactor where fission takes place. It is filled with water and contains the nuclear fuel.

Core Drilling

Technique used to obtain a cylindrical sample of rock during drilling. Unlike regular drilling, which fragments the rock, core drilling provides a sample (called a core sample) that is more representative of the subsurface rock formations.

Core Sample

Cylindrical section of rock obtained by drilling. This sample provides valuable data on the rock's properties, so that investigation can be set based on the interpretation of electrical signals, or logs.


The gradual degradation of a material by a physical or physicochemical reaction with its environment. Corrosion tends to return processed materials to their original state.

Crude Oil

Oil that has not been refined.


(from the Greek kryos, cold) - All the frozen areas of the planet: land glaciers, ice caps (Arctic and Antarctic), icebergs and ice packs, permafrost (permanently frozen ground), frozen lakes and rivers, snow and seasonal ice on the continents.