Glossary - Letter S

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Second Recovery and Enhanced Oil Recovery

All methods utilized to improve on primary recovery through natural depletion, which uses only the difference in pressure between the oil or gas reservoir and the production wells. These methods include artificial lift, one type of which is gas lift (injecting gas micro-bubbles into the production well to reduce the density of the fluid in the fluid column); injecting gas or water into the lower section of the deposit via injection wells; injecting steam to reduce the oil’s viscosity and increase its mobility; chemical flooding (injecting surfactants); and injecting carbon dioxide CO2 (method also used to store CO2).

Secondary Containment System

Berm around a tank to contain leaked substances, to stop them from moving into the environment.

Secondary Energy

Secondary energy is energy produced by converting so-called primary energy, or energy available in its natural state in the environment. Electricity, refined automotive fuel, hydrogen, compressed air and microwave radiation are all types of secondary energy. They are also called energy carriers, because they are easier to transport and most importantly more convenient than primary energy.

Secondary System

A reactor in a nuclear power plant has three major systems: the primary, secondary and cooling water systems. The secondary system recovers heat from the primary system via a heat exchanger and uses it to generate steam. The steam is transferred to the turbine generator, where it is converted into electricity. The secondary system is safety-critical, because it isolates the primary system in the event of accidental radioactive contamination.


Particles of varying sizes formed from the erosion of older rocks, organic residues such as mollusk shells, and the chemical precipitation of some types of carbonates. Over time, sediments are naturally compacted into sedimentary rock.

Sedimentary Basin

Depression in the Earth's crust found on land or in the ocean that collects large quantities of sediment that gradually form layers of sedimentary rock.

Seismic Reflection

Ground waves (vibrations) caused by an explosion or weight drop are sent from a transmitter. These vibrations travel in all directions. When they reach a geological layer, some of the waves are reflected (as a mirror reflects light waves) back to the surface, while others are refracted and continue to go deeper into the ground. Analyzing the reflected waves is a way of building up an image of the subsurface.


Device or system that measures tremors. It comprises a sensor (seismometer) and a recording device that produces seismograms. It is used in seismology and, in some cases, in seismic surveys during exploration.


Material whose initially low ability to conduct electricity (conductivity) can increase depending on other factors such as temperature, luminosity and impurities. The silicon used in photovoltaic panel solar cells is a semiconductor: exposure to sunlight makes it a conductor of electricity.

Separation (Refining)

Various refining processes to separate two phases (liquid/vapor, liquid/liquid or liquid/solid) with differing hydrocarbon compositions. The best-known technique is atmospheric distillation of crude oil, which is the first step in the refining process.

Seveso II Directive

The Seveso directives are European Union directives that require E.U. member states to identify industrial sites that pose major-accident hazards. The directives also require member states to ensure that hazard analyses are conducted, prevention policies and emergency plans are implemented, local residents are sufficiently informed and a competent authority is set up to perform site inspections. After Seveso I in 1982 and Seveso II in 1999, Seveso III, an even more stringent directive published in 2012, will take effect on June 1, 2015.

Shale Gas

Shale gas is found in deeply buried clayey sedimentary rock that is both the source rock and the reservoir for the gas. The low permeability of the rock requires the adaptation of oil extraction techniques such as fracturing and horizontal wells.

Shale Oil

Refers to liquid hydrocarbons extracted from oil shale (see definition) by heating, pyrolysis or hydrogenation.


Mechanical cutting machine used to extract coal in underground mines.

Sievert (Sv)

The unit of measurement for the health effect of low levels of ionizing radiation on the human body. The Sievert corresponds to the gray (ionizing energy absorbed per unit of mass, expressed in weighted by two factors: the biological effectiveness of the type of radiation and the biological impact on the type of tissue affected.


Silicon crystals come from silica, the main compound in quartz and sand. Silicon is a semi-conducting material.

Smart Grid

Power grid that uses new communication and information technology. It is destined to gradually replace the current system, in which production is tied to demand on a simple linear basis, with an interactive system where production will be tailored through more detailed analysis of demand, taking into account information from various points along the distribution chain, particularly the consumer side. The new system will allow greater flexibility when it comes to managing the intermittence of renewable energy and new applications such as electric vehicles.

Solar Panel

A collection of photovoltaic cells connected by wires and covered by glass or a plastic film that protects the cells in bad weather. The solar panel is the base unit of a solar power system: it captures sunlight and converts it into electricity.

Solar Power Tower

Solar power plant that uses sun-tracking mirrors mounted on the ground to focus sunlight on a receiver at the top of a tower.

Source Rock

Sedimentary rock containing large amounts of organic matter and found in deep sea or lake environments. The gradual burial of the source rock together with a rise in temperature generates oil and gas above a certain temperature.

Spot Market

An organized international market where traders buy and sell oil for cash. The volumes or shipments of oil traded exist physically and are delivered immediately or within a very short period of time.

Static Electricity

Static electricity is the accumulation of an electric charge in an insulating material. For example, a plastic ruler rubbed with a dry cloth or a comb run through hair acquires a negative charge by picking up electrons from the cloth or hair. It can then attract small bits of paper, by altering the distribution of their originally neutral electric charge. Electric charges can be released suddenly. Called electrostatic discharge, this is what happens, for example, when you walk on carpet and feel a slight electric shock on touching a metal object. Electrostatics, the branch of physics that studies these phenomena, is governed by Coulomb's law.

Steam Cracking (Refining)

Refining process in which oil reacts with steam at high temperatures. This breaks down (cracks) long, saturated molecules, converting them into shorter, unsaturated ones, which offer greater advantages both technically and in terms of cost. Steam cracking produces large quantities of ethylene and propylene, two major intermediates utilized in the petrochemical industry to create a number of products, including widely used polymers.

Steam Generator

A component that converts water into steam. It is frequently used in power generation processes in thermal power plants and some nuclear power plants. The pressure from the steam drives a turbine generator.

Stirling engine

Invented in 1815 by Robert Stirling, the Stirling engine initially used ambient air, subjected to the standard thermodynamic cycle (compression, heating, expansion, cooling). It aimed to provide a safer alternative to the steam engines of the time, whose boilers frequently exploded. Several different versions of the Stirling version are available today, using various gases (in particular hydrogen and helium) and are used outside the solar power sector, in highly-specific applications (military equipment, space, research).

Stratigraphic Trap

Trap that accumulates oil due to changes in rock properties rather than faulting or folding.

Structural Trap

Trap that forms as a result of changes in the structure of subsurface. Two of the most common structural traps are the anticline trap and the fault trap.


The gradual sinking of a sedimentary basin under the weight of sediments accumulated over millions of years. Subsidence opens up space for new layers of sediment to accumulate, resulting in the stacking of several kilometers of sediment.


Sustainability indicates a state that is sustainable or reasonably manageable over the long term.

Sustainable Development

This term was first defined in the Brundtland Report, published in 1987, as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs”.

Synthesis Gas (Syngas)

Product of industrial-scale thermochemical reactions (including pyrolysis and catalytic reforming of methane) applied to organic matter, coal or natural gas in low-oxygen conditions. Synthesis gas is mainly made up of hydrogen (H2) and carbon monoxide (CO). Formerly used as a fuel (municipal gas and lighting), today it is mainly an intermediate material in the manufacture of chemicals and petrochemical compounds (hydrogen, ammonia, methyl ether, diesel, etc.).