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An underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, or silt) from which groundwater can be usefully extracted using a water well.


Black shale

A thinly bedded shale that is rich in carbon, sulphide and organic material, formed by anaerobic (lacking oxygen) decay of organic matter. Black shales occur in thin beds in many areas at various depths and are of interest both historically and economically.


Carbon Capture & Storage

Carbon Capture and Storage (CCS) is a combination of a number of existing technologies, with the potential to play a major role in the management and reduction of global carbon dioxide (CO2) levels. The CCS process allows for CO2 emissions released during energy production to be captured and stored underground.

Climate and Energy Framework 2030

The EU’s goals for climate and energy in 2030, agreed upon in October 2014.

Conventional gas

Conventional gas is natural gas that is produced by a well drilled into a geologic formation in which the reservoir and fluid characteristics permit the natural gas to readily flow to the wellbore.

Conversion efficiency

The ratio of useful energy output versus the energy required to perform the process.


Energy 2020

The European Commission's report outlining plans to ensure an affordable and secure energy supply.

Energy Roadmap 2050

On 15 December 2011, the European Commission adopted the Communication "Energy Roadmap 2050". The Roadmap outlines the EU's commitment to reducing greenhouse gas emissions to 80-95 per cent below 1990 levels by 2050 in the context of necessary reductions by developed countries as a group. In the Energy Roadmap 2050 the Commission explores the challenges posed by delivering the EU's decarburization objective while at the same time ensuring security of energy supply and competitiveness.

Energy security

A term used to refer to the reliability of future energy supply. This depends on a number of different factors, including the availability of energy supplies, their affordability, and the capacity to extract them in an environmentally sustainable manner.

Evaporation ponds

Artificial ponds with very large surface areas that are designed to allow the efficient evaporation of water through exposure to sunlight and ambient surface temperatures.

Extraction process

The method used for drawing out resources from the ground. For unconventional gas, this is mainly hydraulic fracturing.



See ' Hydraulic fracturing '.

Free gas

Natural gas that is trapped within spaces in the rock, making it more accessible.



The first Shale Gas Research Initiative, is a European interdisciplinary research project with the aim of developing a black shale database. The first phase of the GASH research project was finished and final results were presented in the autumn of 2012. The project is sponsored by the following companies: Statoil, ExxonMobil, Gas de France SUEZ, Wintershall, Vermilion Energy, Marathon Oil, Total, Repsol, Schlumberger and Bayerngas Norge.

GeoEn Project | Website

A collaborative research project focusing on geo-energy, with the aim of enabling a secure and sustainable low-carbon energy supply. The researchers use existing technologies to look at CO2 capture and transport, geological storage of CO2, shale gas and geothermal technologies.


Horizontal drilling

A hydrocarbon well drilling technique that allows for multiple underground wellbores to be deviated from one surface well site.

Hydraulic fracturing

A process through which small fractures are made in impermeable rock by a pressurized combination of water, sand and chemical additives. The small fractures are held open by grains of sand, allowing the natural gas to flow out of the rock and into the wellbore.


An organic compound (as acetylene or butane) containing only carbon and hydrogen and often occurring in petroleum, natural gas, coal and bitumens.


Induced Seismicity

Earthquakes attributable to human activities are called "induced seismic events" or "induced earthquakes." Globally, the vast majority of earthquakes that occur have natural causes. Under very unique circumstances some of these earthquakes can be related to human activities. In these rare instances, the induced seismicity is caused by man-made changes to reservoir pressure or stress, in the presence of an unstable fault and a critical stress state in the rocks.

Generally, seismic events with a magnitude (M) greater than 2.0 have the possibility of being felt, particularly if they occur at shallow depths, but smaller seismic events (M<2.0) generally are not felt.

International Energy Agency

The IEA is an autonomous organization linked with the Organization for Economic Co-operation and Development (OECD). Based in Paris, it works to ensure reliable, affordable and clean energy for its 28 member countries and beyond. Founded in response to the 1973-74 oil crisis, the IEA's initial role was to help countries co-ordinate a collective response to major disruptions in oil supply through the release of emergency oil stocks to the markets.
Today, the IEA's four main areas of focus are: energy security, economic development, raising environmental awareness, as well as engaging non-member countries to find solutions to shared energy and environmental concerns.


Lifecycle Greenhouse gas emissions

The aggregate quantity of greenhouse gas emissions (including direct emissions and significant indirect emissions such as emissions from land use changes), related to the full fuel lifecycle, including all stages of fuel production and distribution, from extraction through the distribution and delivery and use of the finished fuel to the ultimate consumer, where the mass values for all greenhouse gases are adjusted to account for their relative global warming potential.


Liquefied Natural Gas is natural gas that has been cooled to -162 °C to convert the gas temporarily to a liquid state for storage or transportation purposes. As a liquid, natural gas occupies about 600 times less space than when in its gaseous form. LNG is principally used for transporting natural gas to distant markets, where it is re-gasified and distributed via pipelines to consumers.


Modern cycle gas turbine

A gas turbine, also called a combustion turbine, is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. (Gas turbine may also refer to just the turbine element.) It is often used for power generation.


Organic richness

See 'TOC'. Refers to the density of organic material within the rock.



Permeability is the measure of how fluids or natural gas move through the rock (typically measured in "millidarcies")


Porosity measures the open space ("pore space") between grains. The lower the porosity, the more important hydraulic fracturing is to extracting natural gas.



The Registration, Evaluation, Authorization and Restriction of Chemical substances (REACH) is the European Community Regulation on chemicals and their safe use (EC 1907/2006), which entered into force on 1 June 2007. While there is no specific identifier on REACH forms for 'hydraulic fracturing', service providers have been using the 'oil and gas extraction' category; many exploration and production companies active in European unconventional gas exploration already disclose this information on their company website to ensure transparency.

REC or Green Completions

Reduced Emission Completion (REC) technologies filter and capture the methane emissions that are typically contained in high concentrations in flowback water from the hydraulic fracturing process. The captured gas may be sold, resulting in environmental and economic benefits. The process requires a gas pipeline to be laid up to the well-pad prior to production and is now a feature of most new wells in the United States. Starting October 15, 2012, all gas emissions from flowback operations must be captured and combusted. From 2015 onwards, all gas capable of entering the transmission line must be routed to sales.

The use of REC technology in European shale gas wells is made all the more commercially interesting because the value of the gas captured is higher. Moreover, proper planning, favored by the existing European licensing framework, allows for a timely coordination of drilling and pipeline installation. Industry is working with suppliers to ensure that the availability of REC equipment keeps up with demand.

Recovery rate

The rate at which natural gas can be removed from a reservoir.


Gas reserves are defined as technically recoverable gas resources (see below). This means that the reserves can be extracted from the ground using current technologies; however it does not guarantee that this extraction process can be achieved in an economically viable manner.


A naturally occurring storage area below the earth's surface, characteristically a folded rock formation that traps and holds natural gas. The reservoir rock must be permeable and porous to contain the hydrocarbons, and it has to be capped by relatively impermeable rock layers in order to form an effective seal and prevent the hydrocarbons from escaping. Reservoirs are routinely described as either "conventional" or "unconventional".

Typical conventional reservoir rocks are sedimentary and include sands, sandstones, arkoses, and fissured limestone and dolomite. Also of interest are reservoirs commonly referred to as "unconventional", including shale reservoirs, tight sandstone reservoirs, "coal-bed-methane" reservoirs, and tight oil reservoirs. The main difference between conventional and unconventional reservoirs is that unconventional resources require some form of stimulation to produce commercial volumes of hydrocarbon at commercial rates.

Further, unconventional gas resources are generally not buoyancy-driven accumulations; and are regionally pervasive accumulations, most commonly independent of structural and stratigraphic traps. In unconventional gas and tight oil reservoirs, the main challenge is to improve the permeability of the rock through which the hydrocarbons flow. This is done through hydraulic fracturing which creates fissures in the rock increasing its permeability, releasing the hydrocarbons from the pores in which it is trapped, and allowing the hydrocarbons to flow to the well.


Gas resources represent all natural gas contained in a reservoir without regard to technical or economic recoverability.


Sedimentary rock

Sedimentary rock is one of the three main rock groups (along with igneous and metamorphic rocks) and is formed in three main ways—by the deposits of the weathered remains of other rocks; by the deposits of the results of biogenic activity; and by precipitation from solution. Sedimentary rocks include common types such as chalk, limestone, sandstone, and shale.

Shale basins

The underground rock formations that serve both as natural gas generators and reservoirs.

Shale Gas Research Initiative (GASH)

GASH is the first European interdisciplinary shale gas research initiative. Based in Germany, GASH started in 2009 and the first phase runs for three years. Besides the development of a GIS-based European black shale database, 12 research projects are being conducted by a multinational expert task force drawn from research institutions, geological surveys, universities and consultants.

The overall project goal is to predict shale gas formation and occurrence in time and space. GASH focuses on the potential gas shale of Europe, especially on the Alum shale (Denmark), and the Posidonia and Carboniferous shales in Germany. Importantly, it also integrates proven U.S. gas shales (e.g. Barnett Shale) for calibration of key variables.


Slick water fracturing is a method or system of hydraulic fracturing that involves adding chemicals to water to increase the fluid flow. Slickwater increases the speed at which the pressurized fluid can be pumped into the wellbore.

Surface footprint

The ground space utilized to undertake industrial operations including natural gas extraction.



Generated or formed by heat, especially via physiological processes.

Total Organic Carbon (TOC)

The concentration of material derived from decaying vegetation, bacterial growth and metabolic activities of living organisms or chemicals in the source rocks.


Unconventional Gas

An umbrella term for natural gas that is produced by means that do not meet the criteria for conventional production. See Conventional gas above.

Note: What is qualified as "unconventional" at any particular time is a complex interactive function of resource characteristics, the available exploration and production technologies, the current economic environment, and the scale, frequency, and duration of production from the resource. Perceptions of these factors inevitably change over time and they often differ among users of the term.



The channel created by the drill bit.