"The language of CCS"

Definitions and explanations

Authors: Kelvin Boot1, Samuela Vercelli2, Leslie Mabon3, Simon Shackley3, Salvatore Lombardi2.

1Plymouth Marine Laboratory
2University of Rome Sapienza – CERI
3University of Edinburgh

Aknowledgements: we would like to thank the ECO2 research community which has participated, contributed and provided feed-back for the development of this document; thank you also to the colleagues that have made available on the web, glossaries and other useful materials on which we have built.

Contact author: Kelvin Boot (PML)



A reduction in the amount, degree or intensity of emissions like CO2


The process by which one substance, such as a solid or liquid, takes up another substance, such as a liquid or gas, through minute pores or spaces between its molecules. A paper towel takes up water, and water takes up carbon dioxide, by absorption.

Active project

A project under construction or in operation. An active project can be under construction (execute/execution stage) or in operation (operate/ operational stage). In CCS terms an active project means from when the first CO2 injection starts until CO2 injection has ceased and the site is relinquished. Active projects are those that have a valid storage permit, even if responsibility passes to another agency or organisation such as the relevant state authority.


(in CCS) The process by which a material attracts carbon dioxide to its surface so it can be captured and/or stored.


Derivatives of ammonia used as solvents in post combustion CO2 capture process to absorb carbon dioxide from the flue gas stream. The amine is heated to release high purity CO2 and the CO2-free amine is then reused. This technique can be used in power plants for cleaning of flue gas stream. (Power Plants)


This term describes effects, processes, objects, or materials (such as climate change gases) derived from human activities, as opposed to those occurring naturally and without human influence.


Folded geological strata that is concave downwards (convex upwards)


The technical term for a geological structure whose rock is permeable, or porous enough to allow significant flow of fluids. Aquifers are bound by natural seals like cap-rock. Aquifers closer to the surface of the ground often contain freshwater suitable for human consumption, deeper aquifers are usually filled with salt water – these are called saline aquifers (however some suggest that the term saline formation might be a better substitute as it avoids any confusion with aquifers for water supply) – and maybe suitable for CO2 storage.


A rock which contains no interconnected openings or interstices and therefore neither stores nor transmits water (USGS).


A confining bed that retards but does not prevent the flow of water to or from an adjacent aquifer; a leaky confining bed. It does not readily yield water to wells or springs, but may serve as a storage unit for ground water (USGS) (AGI, 1980).


The layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%).



A type of basic igneous rock which is typically erupted from a volcano. May have porosity and permeability in the fractures or cavities between blocks of solid rock.

Basel Convention

UN Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal, which was adopted at Basel on 22 March 1989.


A geological region with strata dipping towards a common axis or centre, so forming a ‘basin’ shape.


Pertaining to the depth of water above the seabed.


Pertaining to conditions on the seafloor. Used as a descriptive term for the animals and plants that live on the seabed (the benthos). Benthic organisms, may be fixed to the substrate, may burrow through it or move across it.


A collection of organisms living on a lake or seabed.

Bio-accelerated sequestration

A concept of using microbial organisms (microscopic plants or animals) with CO2, in geologic formations, to sequester the CO2 and/or convert it to methane.


A large scale technology intended to combine sustainable biomass conversion with CO2 Capture and Storage – e.g. in biofuels and bio-energy production. It is already being used in the USA.


An organism or biological response that reveals the presence of pollutants or other impacting factors, by the occurrence of typical symptoms or measurable responses.

Biological indicators

Species which can be used by observers to determine how various conditions in an environment have changed over time.

Biomass-based CCS

CO2 capture and storage in which the feedstock is Biomass.


An organism that provides quantitative information on the quality of the environment around it.


That part of the Earth and its atmosphere which supports life or is capable of supporting living organisms.


An uncontrolled eruption of oil or gas from wells during drilling or from abandoned wells subject to repressurisation . Like many other terms CCS has borrowed this from the hydrocarbon industry to describe an uncontrolled eruption of CO2 from an injection, a monitoring or an abandoned well.

Brine formation
Brine water

Water with a salt concentration greater than 35 parts per thousand (3.5%). Sea water has a similar average concentration. Brines in underground formations can contain 20% salt or more.

Bulk CO2

Unprocessed gaseous CO2, with a CO2 content typically in excess of 95%


The upward force acting on an object placed in a fluid – the force is equal to the weight of fluid displaced by the object. There is a tendency of a fluid or solid to float on or rise through a fluid of higher density.



Calcium carbonate


Calcium oxide


Layer of rock that is very difficult to permeate, allowing it to act as an upper seal to prevent liquids and gases from flowing out of a formation or reservoir. Anhydrite, gypsum, limestone, sulphur, and clay rocks can form caprocks.

Capillary action

The movement of water in the interstices of a porous medium due to capillary forces (USGS, ASTM, 1990).


The removal of CO2 resulting from fossil fuels’ use.

Capture efficiency

The fraction of CO2 separated from the gas stream of a source.

Carbon credit

A convertible and transferable instrument that allows an organization to benefit financially from an emission reduction. (CO2 NetEast)

Carbon Dioxide (CO2)

A colourless, odourless gas formed by carbon and oxygen to be found in the atmosphere and in the underground. It is derived from many sources: volcanic eruptions, rock alterations, decomposition of organic matter, combustion of fossil fuels, etc. It is also produced when animals (including humans) breathe. Carbon dioxide is essential to the photosynthesis process that sustains plant, upon which many animal species, in turn, rely. Although relatively non-hazardous, it can create lethal oxygen-deficient environments in high concentrations (especially in confined spaces). It is one of the greenhouse gases. Since over the last 200 years its concentration in the lower atmosphere has increased from 270 parts per million (PPM) to 380 ppm.

Carbon dioxide as a pollutant

There is some debate as to whether CO2 should be regarded as a pollutant. One argument says that it should not be as it is a naturally occurring substance essential for life. However even useful substances in the wrong place and in excess can become polluting, for example iron is needed as a micro nutrient but becomes a pollutant at high concentrations.

Carbon dioxide sequestration

The fixation of CO2 and other greenhouse gases by natural systems such as forests or phytoplankton, that would otherwise remain in the atmosphere. In natural systems plants and oceans sequester carbon for utilisation in life processes such as growth of tissue. Carbon dioxide sequestration in CCS context is often regarded as synonymous with and replaced by the term carbon dioxide storage i.e. (The term “carbon sequestration” is used to describe both natural and deliberate processes by which CO2 is either removed from the atmosphere or diverted from emission sources and stored in the ocean, terrestrial environments (vegetation, soils, and sediments), and geologic formations. (USGS Fact sheet 2008-3097. Carbon Sequestration to Mitigate Climate Change. For the purposes of this glossary sequestration is best reserved for natural systems, storage is regarded as a human activity following active capture for removal to prevent CO2 entering the atmosphere.


Carbon capture ready. See CCSR


Abbreviation for Carbon Capture and Storage or Carbon dioxide Capture and Storage. The two terms are used interchangeably, for reasons of clarity and consistency Carbon dioxide Capture and Storage should be preferred.


A CCSR facility is a large-scale industrial or power source of CO2 which could and is intended to be retrofitted with CCS technology when the necessary regulatory and economic drivers are in place. (


Carbon capture, use and storage (originated as a term in China) or (US DOE) carbon capture, utilisation and storage. This term reflects a growing ambition to make use of CO2, possibly even to profit from its capture. EOR is one example of CCUS, biochar another, where charcoal is produced and added to soils where its contained carbon is locked away, or re-used by growing plants.

Climate change

Defined by the United Nations Framework Convention on Climate Change (UNFCCC) as “change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods”.

Closure of a storage site

Means the definitive cessation of CO2 injection into that storage site.


Carbon monoxide

CO2 avoided

The difference between CO2 captured, transmitted and/or stored, and the amount of CO2 generated by a system without capture, net of the emissions not captured by a system with CO2 capture.

CO2 capture

The removal of CO2 from a process stream or from the atmosphere to produce a highly pure stream of CO2 amenable for conversion or storage. CO2 capture systems are assessed on the purity of the captured CO2, the percent of total CO2 that is captured, and the capital cost and energy use per unit of CO2 captured.

CO2 equivalent

A measure used to compare emissions of different greenhouse gases based on their global warming potential. If CO2 is given a value of 1; methane is 25 times more potent; and nitrous oxide 298 times more powerful than CO2. Global warming potential is one, very important measure, but total amounts being emitted to the atmosphere are a very significant factor, which make CO2 especially worrying.

CO2 fixation

The immobilisation of CO2 by its reaction with another material to produce a stable compound. (CO2 NetEast).

CO2 plume

The dispersing volume of carbon dioxide within the geological formation or other medium, such as seawater during a seep.

CO2 reuse

A practical application of captured, concentrated CO2 that adds value and which can partially offset the cost of CO2 capture as a transitional measure to assist the accelerated uptake of CCS. (see also CCUS).

CO2 stream

A flow of substances that results from CO2 capture processes. This could be from a factory along pipework, for example.


European Network of Excellence on the Geological Storage of CO2 is an Association of 13 research institutes from 7 European countries, engaged for scientific advancement in the field of CO2 storage (


Put under pressure so that more gas will fit into the same volume; with carbon dioxide it is compressed until it is like a dense fluid.


Conservation of Clean Air and Water in Europe.

Confining zone

A geological formation, group of formations, or part of a formation that is capable of limiting fluid movement above an injection zone (USGS)(40 CFR 146.3).

Connate pore fluids

Fluids that are captured in the pores of sedimentary rocks as they form.


Restriction of movement of a fluid (such as supercritical CO2) to a specific place or space (like a storage aquifer or an oil or gas field in disuse).


Any non-CO2 substance associated with the stored CO2 and any associated leaks, including any impurities that might be associated with the injected CO2 stream, and any substances that might be released or formed as a result of sub-surface storage and/or leakage of CO2.

Corrective measures

Any measures taken to correct significant irregularities or to close leakages in order to prevent or stop the release of CO2 from the storage complex. (EC)

Critical point

The temperature and pressure point above which carbon dioxide gas and liquid phases cannot exist as separate phases.



In terms of local geology anything within the bedrock is considered deep while anything in the overlying unconsolidated sediments is considered shallow. In CCS terms deep usually refers to depths greater then 800 metres.

Deep coal seam

A seam which is too deep to be mined economically. Often suitable for CO2 injection/storage. CO2 is adsorbed to the coal typically replacing methane. This methane can then be recovered.

Deep saline aquifer

An underground rock formation deep beneath the surface of the earth that is made up of permeable materials and containing highly saline fluids, and which may be suitable for storage of CO2. The most suitable reservoirs are those at depths greater than 800m

Demonstration phase

Demonstration phase usually means that the technology is implemented in a pilot project or on a small scale, but not yet economically feasible at full scale. However, because of the nature of CO2 storage projects it is deemed necessary to demonstrate efficacy on a larger scale to demonstrate costs and technologies realistically.

Depleted gas fields

Underground rock where most of the economically viable gas has already been extracted by traditional means from between the grains of rock.

Depleted oil fields

Underground rock where most of the economically viable oil has been already been extracted from between the grains of rock.

Depleted reservoir

A structure like an oil or gas reservoir where production has ceased or has significantly reduced from past exploitation.


Processes that cause changes in sediment after it has been deposited and buried under another layer.


Department of Energy (United States).

Dry ice



The European Biofuels Technology Platform. (


Enhanced Coal Bed Methane Production (recovery), the use of CO2 to enhance the recovery of the methane present in unminable coal beds through the preferential adsorption of CO2 on coal.


FP7 research project that will establish a framework of best environmental practices to guide the management of offshore CO2 injection and storage and as addendum to the EU directive on “Geological Storage of CO2” for the marine realm. This includes the quantitative assessment of potential and actual impacts on marine ecosystems at a CO2 injection facility and the entire storage site. A comprehensive monitoring concept for storage sites will be developed comprising innovative techniques that are apt to detect different modes and levels of leakage including that of pre-cursors. Field studies at operated and prospective sites (Sleipner, Snøhvit) and natural CO2 seeps (North Sea, Mediterranean Sea) are completed by lab experiments and numerical simulations on different scales. An integral part of the project is to transfer this knowledge into a risk management concept and an economic valuing of the costs of leakage, monitoring, mitigation measures, and a clear communication framework. An understanding of the precautionary principle as primary tool for balancing the environmental risks will be built. (Abstract from

Economic Potential

The amount of greenhouse gas emissions reductions from a specific option that could be achieved cost-effectively, given prevailing circumstances (the price of CO2 reductions and costs of other options). The estimated range of economic potential for CCS over the next century is roughly 200 to 2,000 GtCO2.


A dynamic community of plants, animals and microbes together with their physical environment; a natural system with interacting and interdependent relationships.

Eliminatory criteria

A potential storage site that does not pass these criteria would not normally be considered for CO2 storage. There are three categories:

critical – failure to meet any of these would deem the site as being not suitable;

essential – if one of these (seismicity, faulting and fracturing, size, hydrogeology) is not met but the others are there may be case for further consideration;

desirable – there are 14 criteria in this section, none of these is eliminatory in itself, and a potential site that ‘fails’ to satisfy several of these may still be considered, but too many would result in further consideration is a likely requirement. (For further detail on the Eliminatory Criteria please see Bachu, S. Screening and selection criteria, and characterisation techniques for the geological sequestration of carbon dioxide (CO2) in: Maroto-Valer, M. Mercedes; Developments and innovation in carbon dioxide (CO2) capture and storage technology. Woodhead Publishing Ltd., 2010.


For the purposes of the United Nations Framework Convention on Climate Change (UNFCCC) - “Emissions” means the release of greenhouse gases and/or their precursors into the atmosphere over a specified area and period of time.

Enhanced coalbed methane production (ECBM)

When CO2 is injected into coal beds, it displaces methane molecules that are attached to the surface of the coal. This methane that is dislodged from the coal is then free to move about in the coal, and it can be pumped out of the bed. This methane extraction process is referred to as “Enhanced Coal Bed Methane” or “ECBM”. (USGS)

Enhanced Gas Recovery

The incremental gas recovery from depleted conventional gas reservoirs. EGR is usually achieved by pumping another substance into the reservoir to ‘push out’ the remaining gas for economic use. CO2 can be used for this purpose and provide the bonus of CO2 storage. As gas is removed from natural gas reservoirs, the pressure of the reservoir decreases. As the pressure within the reservoir decreases, it becomes more difficult to recover more gas. By injecting CO2 into the natural gas reservoir, the pressure of the reservoir is increased, and more gas can be recovered (USGS).

Enhanced Oil Recovery (EOR)

CO2 can be injected into depleted oil reservoirs to enhance oil recovery from the reservoir. CO2 will dissolve into the residual oil in place, which lowers the viscosity of the oil. The lower viscosity enables the oil to flow more easily, which makes it possible to extract more oil from reservoirs (USGS definitions). EOR is a generic term for techniques for increasing the amount of crude oil that can be extracted from an oil field. It is also known as improved oil recovery or tertiary recovery. Using EOR 30–60% more of the reservoir’s original oil can be extracted compared to 20–40% using primary and secondary recovery. Fluids (such as steam of CO2) injected into the reservoir ‘push’ the oil out.

Enhanced weathering

The process by which carbon dioxide is sequestered from the atmosphere through the dissolution of silicate minerals on the land surface. (International Journal of Greenhouse Gas Control: The potential of enhanced weathering in the UK. July 2012).

Environmental Impact Assessment (EIA)

Environmental Impact Assessment (EIA) is a process of evaluating the likely environmental impacts of a proposed project or development, taking into account inter-related socio-economic, cultural and human-health impacts, both beneficial and adverse. UNEP defines Environmental Impact Assessment (EIA) as a tool used to identify the environmental, social and economic impacts of a project prior to decisionmaking. It aims to predict environmental impacts at an early stage in project planning and design, find ways and means to reduce adverse impacts, shape projects to suit the local environment and present the predictions and options to decision-makers. By using EIA both environmental and economic benefits can be achieved, such as reduced cost and time of project implementation and design, avoided treatment/clean-up costs and impacts of laws and regulations. (Convention on Biological Diversity -


(of a gas, liquid, or heat) leak from a container, e.g. ‘the CFCs have escaped into the atmosphere’; to break free from control. In a CCS context a leak would be an unintentional escape from geological storage.

EU Geocapacity

A European research project to assess the total geological storage capacity in Europe for anthropogenic CO2 emissions.


European Union Saline Aquifer Carbon Dioxide Storage Programme.


The assessment of potential storage complexes for the purposes of geologically storing CO2 by means of activities intruding into the subsurface such as drilling to obtain geological information about strata in the potential storage complex and, as appropriate, carrying out injection tests in order to characterise the storage site (EC).



In geology a natural break in the rocks, with one side moves relative to the other. This movement may be lateral, vertical or a combination of both.


A Feature that represents a component of a storage system or an Event or Process relevant to its evolution. The term includes ‘external’ FEPs or EFEPs that are part of the global system but external to the storage system; the EFEPs may however act upon the system to alter its evolution (e.g. seismic effects). Together, the FEPs of the system describe conceptual models that may be related to scenarios for system evolution.


The immobilisation of CO2 by its reaction with another material to produce a stable compound. (Co2 fixation)


The injection of a fluid into an underground reservoir.

Flue gas

Flue gas is gas that exits via a flue, which is a pipe or channel for gases from a fireplace, oven, furnace, boiler or steam generator. It often refers to the combustion exhaust gas produced at power plants. Its composition depends on what is being burned, but it usually consists of carbon dioxide (CO2), water vapour and nitrogen (typically more than two thirds) derived from the combustion air as well as excess oxygen (also derived from the combustion air). It further contains a small percentage of pollutants such as particulate matter, carbon monoxide, nitrogen oxides and sulphur oxides.

Fossil fuel

A general term for buried combustible geologic deposits of organic materials, formed from decayed plants and animals that have been converted to crude oil, coal, natural gas, or heavy oils by exposure to heat and pressure in the Earth’s crust over hundreds of millions of years; they are hydrocarbons which produce CO2 and other gases when burned.


A break in rock along which no significant movement has occurred. (CO2 NET- East).


Geochemical trapping

The retention of injected CO2 by geochemical reactions.(see Trapping, geochemical)

Geological formation

A geologic formation is a formally named rock stratum or geological unit. It is a rock unit that is distinctive enough in appearance that a geologic mapper can tell it apart from the surrounding rock layers and is the fundamental unit of lithostratigraphy (the scientific study and categorisation of rock strata based on their lithology - colour, texture, and composition). The concept of formally defined layers or strata is central to the geologic discipline of stratigraphy. Some geological formations are suitable for storing CO2. Nongeologists may refer informally to outcroppings of rock or interesting geological features as geological formations, even though this is not technically correct.

Geological storage

see Storage, geological.


A European research project which determined the geological storage of CO2 possibilities in eight countries (Norway, Denmark, UK, Belgium, Netherlands, Germany, France and Greece)

GHG (GreenHouse Gas)

Greenhouse gases: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulphur hexafluoride (SF6). GHGs are responsible for maintaining the Earth at a habitable temperature, but rising temperatures and ultimately global warming result from an imbalance leading to an increase in GHGs.

Global Warming Potential (GWP)

A measure of the magnitude of the heattrapping effect resulting from the addition of 1 kilogramme of a gas to the atmosphere relative to that of 1 kilogramme of carbon dioxide. GWP is a function of two factors (1) the instantaneous heat-absorbing ability of the gas, and (2) the length of time that emissions of the gas persist in the atmosphere, on average. See CO2 equivalent.


(in CO2 storage) Geological formations where no hydrocarbon production has occurred within the potential storage area; (in CO2 capture) new facilities where none previously existed

Greenhouse effect

A naturally occurring process that aids in heating the Earth’s surface and atmosphere. It results from the fact that certain atmospheric gases, such as carbon dioxide, water vapour, and methane, are able to change the energy balance of the planet by absorbing longwave radiation emitted from the Earth’s surface. Without the greenhouse effect life on this planet would probably not exist as the average temperature of the Earth would be a chilly -18° celsius, rather than the present 15° celsius.

Greenhouse gas

see GHG




Hazardous and non-hazardous waste

Potentially harmful and non-harmful substances that have been released or discarded into the environment.

Host rock

In geology, the rock formation that contains a foreign material. In CCS a rock that receives stored CO2.

Hydrodynamic trap

Hydrodynamic traps are quite rare. High water saturation of low-permeability sediments reduces hydrocarbon permeability to near zero, resulting in a water block and an accumulation of petroleum down the structural dip of a sedimentary bed below the water in the sedimentary formation. (Encyclopaedia Britannica)


The branch of geology dealing with the waters below the earth’s surface and with the geological aspects of surface waters (hydrogeological is the adjective)



International Energy Association


International Energy Agency – Greenhouse Gas R&D Program. An international partnership that aims to evaluate technologies for reducing GHG emissions, disseminate the results of these studies, and identify targets for research, development and demonstration.


Measure of the consequences of one thing upon another

Impact assessment

A method of assessing the consequences of individual actions or projects. See Environmental Impact Assessment


A substance that cannot be penetrated. A rock or material that stops the movement of water or other liquids through it.

Injection of CO2 into geologic reservoirs

CO2 will be pumped into geologic formations from the surface, most likely as a dense, liquid-like fluid (also known as a “supercritical fluid”) into either a coal bed, or a saline aquifer or hydrocarbon reservoir. If the CO2 is injected into a depleted hydrocarbon reservoir, then additional petroleum or natural gas could be extracted (Enhanced Oil Recovery or Enhanced Gas Recovery). If the CO2 is injected into a coal bed, then methane could be liberated and extracted (Enhanced Coal Bed Methane). (USGS definitions)

Injection well

Well used for injecting fluids into the subsurface. (USGS)

Injection zone

A geological “formation,” group of formations, or part of a formation receiving fluids through a well (40 CFR Part 146.3).


IPAC-CO2 Research Inc., the International Performance Assessment Centre for Geologic Storage of Carbon Dioxide, is an environmental nongovernment organization (ENGO) created to provide independent risk and performance assessments of CO2 storage projects.


Intergovernmental Panel on Climate Change.


Lake Nyos

Lake Nyos, Cameroon, West Africa was the site of a limnic eruption in 1986, which released 80 million cubic metres of CO2 from the lake, killing at least 1700 people. This event is often mistakenly cited as an example of the possible consequences of leakage from a CO2 storage site. In reality the case of Lake Nyos is related to volcanic activity where CO2 is produced continuously and thus the pressure in the reservoir increases continuously. In the case of a CO2 storage site similar phenomena could not happen; as is also demonstrated by natural gas reservoirs (CO2, methane, etc.) where such catastrophic phenomena have never occurred.


Life Cycle Assessment. (LCA) is a tool that can be used to assess the environmental impacts of a product, process or service from design to disposal i.e. across its entire lifecycle, a so called cradle to grave approach. The impacts on the environment may be beneficial or adverse. These impacts are sometimes referred to as the “environmental footprint” of a product or service (RSC).


To permit the escape, entry, or passage of something through a breach or flaw. In CCS terms there is a sense of an accidental or unintentional escape of injected fluid from storage.


Leakage in CCS terms is, for example in the CCS-Directive, “any release of CO2 from the storage complex (Art.3 (5) CCS-directive)“ or “in respect of carbon storage, the escape of CO2 from the storage formation (see below) in the water column and the atmosphere.” (The Risk Assessment and Management Framework for CO2 Sequestration in Sub-seabed Geological Structures (FRAM) in the context of the London Protocol, p.31)

Limnic eruption

Also referred to as ‘lake overturn’ is a rare natural disaster related to volcanic activity in which dissolved CO2 suddenly erupts from deep lake water, suffocating any wildlife, livestock and humans it overwhelms. Landslides, volcanic activity and explosions can trigger such ‘eruptions’.To date, only two occurrences have actually been observed: at Lakes Monuon and Nyos in Cameroon, West Africa.


science of the nature and composition of rocks.


The outer layer of the Earth, made of solid rock, which includes the crust and uppermost mantle up to 100 km thick.

Lithostatic pressure

the pressure or stress imposed on a layer of soil or rock by the weight of overlying material.


Loss of Containment is the release or escape of material, usually gas or liquid, contained inside plant equipment or piping such that it can enter the immediate environment of the plant and potentially migrate outside of the plant boundaries (CRC NetBase).

London Convention

On the Prevention of Marine Pollution by Dumping of Wastes and Other Matter - adopted at London, Mexico City, Moscow and Washington in 1972.



Maximum allowable operating pressure. The maximum pressure that a pipe or container can safely hold in normal operations.

Measurement, Monitoring, and Verification (MM&V)

MM&V is defined as the capability to measure the amount of CO2 stored at a specific sequestration site, to monitor the site for leaks or other deterioration of storage integrity over time, and to verify that the CO2 is stored and not harmful to the host ecosystem. MM&V capability will ensure safe permanent storage, reduce the risk associated with buying or selling credits for sequestered CO2, and help satisfy regulators and local government officials who must approve large sequestration projects. MM&V will also provide valuable feedback for continual refinement of injection and management practices.


(in CCS) .Thin sheets of material that can separate carbon dioxide from other gases – acts like a sieve.


refers to movement of fluids (including injected CO2) driven by pressure or density differential within the injection formation. This can involve movement both vertically and horizontally within the designated injection horizon. The fluids remain “trapped” by both the upper and lower bounding seal layers.

Mineral Carbonisation (Mineral Carbonation)

A process in which CO2 reacts with magnesium or calcium oxide to form mineral carbonates. The mineral carbonates are unreactive solids - highly permanent carbon storage. Challenges include slow reaction rates and the large tonnage of mineral-rich earth that must be mined for each unit of CO2 sequestered.

Mineral trap

A geological formation that retains fluids through the reaction of the fluid-forming a stable mineral.

Mineral trapping

Is a natural form of geologically storing CO2 by the very slow reaction between CO2 and naturally occurring minerals, such as magnesium silicate, to form the corresponding mineral carbonate.



Natural analogue

A natural occurrence that mirrors in most essential elements an intended or actual human activity. In CCS terms natural occurring CO2 or other gases (methane mainly) reservoirs from which much can be learned regarding trapping mechanisms, cover rock efficiency and eventually gas migration mechanisms to the surface where seeps exist. A subset of Natural Analogue are volcanic and geothermal areas where evident gas emanations (gas vents) occur. These areas are examples of unsuitable sites for CO2 storage but are useful ‘natural laboratories’ for studying gas migration mechanisms, the effects of gas emanations on terrestrial and marine life and for testing monitoring tools.

Natural gas

Gas stored underground; it consists largely of methane, but can also contain other hydrocarbons, water, hydrogen sulphide and carbon dioxide. These other substances are separated before the methane is put into a pipeline or tanker.

Natural underground trap

A geological structure which retains fluids by natural processes.


Norsk Sokkels Konkuranseposisjon – Standards developed by the Norwegian Technology Centre.


Ocean Injection

A concept for ocean sequestration in which CO2 is injected directly into the mid-or deep ocean waters, where it dissolves into the ocean water. (IPAC CO2).

Ocean Sequestration

Storage of CO2 in ocean waters. Oceans are an important part of the natural carbon cycle because they store, release, and absorb large quantities of CO2 to and from the atmosphere. Research in this area is focused on learning more about the ocean carbon cycle, deep ocean ecosystems, and the safety and potential environmental impacts of CO2 storage. (IPAC CO2). See Ocean Storage. This is to be distinguished from sub-seabed storage where CO2 is buried deep beneath the seabed in geological strata.

Ocean storage

A proposed method whereby CO2 is injected into the deep ocean (greater than 1000m depth), where most of it would remain isolated from the atmosphere for centuries.


Organisation for Economic Cooperation and Development.


Convention for the Protection of the Marine Environment of the North-East Atlantic, which was adopted at Paris on September 22, 1992. (OSlo and PARis).


Rocks and sediments above any particular stratum.


Pressure created in a reservoir that exceeds the pressure inherent, and normally expected, at the reservoir’s depth. It is caused by the inability of connate pore fluids (see above) to escape as the surrounding mineral matrix compacts under pressure.

Oxy-fuel combustion capture

Burning a fuel in oxygen-rich gas. The oxygen is separated from the air, and it makes it easier to separate the carbon dioxide from the waste gases.

Oxyfuel combustion

The Oxyfuel combustion process eliminates nitrogen from the flue gas by combusting the fuel in a mixture of oxygen and recycled flue gases. After combustion, the flue gas is cleaned. The cleaned flue gas primarily consists of CO2 and water vapour. By cooling the flue gas, the water vapour condenses thereby creating an almost pure CO2 stream. The CO2 can be compressed, dried and further purified before being transported to a storage site.



Ability of porous and fractured material to allow fluids to flow across it. In CCS, it refers for instance to the ability of a porous rock, such as sandstone, which acts like a sponge to allow the injected CO2 to fill the tiny spaces between grains of the rock (see pore spaces).


Is a measure of hydrogen ion concentration; a measure of the acidity or alkalinity of a solution. (Chemistry Glossary: pH 7 is neutral, a solution with pH less than 7 is said to be acidic; a pH greater than seven is basic or alkaline.


Pipelines and Hazardous Materials Safety Adminstration.

Pilot plant

The pilot plant is the necessary link between initial engineering and the demo plant. The purpose of the pilot plant is to validate the engineering work, to learn and better understand the technology and to demonstrate it.


in CCS the dispersing volume of CO2 in the geological formation (Sitechar).

Pore space

Tiny space between the grains of a rock, usually occupied by a fluid of some sort, often water.


percentage of the volume of a rock that is not occupied by mineral. The gaps are pores and may be filled with various fluids such as salt water, oil, methane, or CO2.

Post-combustion capture

Separating carbon dioxide from other waste gases after a fuel is burnt.

Potential, Technical

Technical potential is the amount by which it is possible to reduce greenhouse gas emissions by implementing a technology or practice that already has been demonstrated.

Pre-combustion capture

Reacting the fuel to form a syngas made up of carbon dioxide, carbon monoxide and hydrogen; Carbon dioxide can be captured before the hydrogen is then burnt. It is also possible to convert the carbon monoxide to carbon dioxide and capture that as well, leaving only the hydrogen as a fuel to burn.


A risk rating is based on the probability of impact and the level of impact.
0 – 10% or Very unlikely to occur.
11 – 40% or Unlikely to occur.
41 – 60% or May occur about half of the time.
61 – 90% or Likely to occur.
91 – 100% or Very likely to occur.
(from Risk Management – Standard processes/definitions: probability of occurrence. occurence.html).


In terms of CCS, projects fall into the categories of: In Planning; Cancelled or Dormant; Pilot; Operational; and Finished. There are currently eight operational sites worldwide, of which three (Sleipner, Snøhvit and K12-B are offshore, sub-seabed). Locations and more details of these can be found at http://, where a useful interactive global map of all categories of projects can be accessed.


An area with separate but similar geological formations.



Reduction-oxidisation reaction.

Regional scale

A geological feature that crosses an entire basin (see basin).


A subsurface body of rock with the porosity and permeability to store and transmit fluids.

Reservoir trap/seal

Hydrocarbons accumulation (oil and gas field) are found in geological traps below the earth surface. The fundamental characteristic of a trap is an upward convex form of porous and permeable reservoir rock that is sealed above by a denser, relatively impermeable cap rock (e.g., shale or evaporites). The trap may be of any shape, the critical factor being that it is a closed, inverted container. Deep reservoirs are, for the purposes of CO2 sequestration, defined to be deeper than 1 kilometer. (USGS definitions).

Reservoir, hydrocarbon

A porous and/or fractured permeable underground formation containing an individual and separate natural accumulation of producible hydrocarbons (crude oil and/or natural gas), which is contained by impermeable rock or water barriers and is characterized by a single natural pressure system.

Risk Management

entails the application of a structured process to identify and quantify the risks associated with a given process, to evaluate these,[…], to modify the process, to remove excess risks and to identify and implement appropriate monitoring and intervention strategies to manage the remaining risks“ (IPCC Special Report, p.251)”

Risks due to leakage

Global – a release that contributes significantly to climate change if some fraction leaks to the atmosphere.

Local – hazards of local significance such as may affect humans, ecosystems, groundwater. There are two types of scenario for local leaks: injection well failures or up abandoned wells, which could create a sudden and rapid release of CO2; and leakage through undetected faults, fractures or leaking wells where the release is more gradual and diffuse, primarily affecting drinking water aquifers and ecosystems where CO2 accumulates between the surface and the top of the water table. (IPCC)


Saline formation

Underground rock where brackish water or brine occupies the tiny spaces between the grains of rock.

Saline groundwater

Groundwater in which a high quantity of salts is dissolved.

Saturated zone

Part of the subsurface that is totally saturated with groundwater.


A plausible description of the future based on an internally consistent set of assumptions about key relationships and driving forces. Note that scenarios are neither predictions nor forecasts. Scenarios can be quantitative (numerical), qualitative (textual) or a mixture of both.


Borderline between the free water and the top of the bottom sediment.


An impermeable rock that forms a barrier above and around a reservoir such that fluids are held in the reservoir: a rock formation which it is very difficult for carbon dioxide and other subsurface fluids to move through under normal conditions.

Secondary recovery

Recovery of oil by artificial means, after natural production mechanisms like overpressure have ceased.

Sedimentary basin

Natural large-scale depression in the earth’s surface that is filled with sediments.(basin)


To pass slowly through small openings or pores; to ooze. In CCS terms it is often reserved for a naturally occurring release of CO2, from an underground source, such as might be seen in parts of Italy, and in the Mediterranean, for example.


The fluid (or amount of fluid) discharged at a seep.

Selection criteria

favourable characteristics that would make a site preferable to another, all other considerations being equal. Failure to meet a selection criterion would not eliminate a site, it will only reduce its desirability or suitability. (see eliminatory criteria). Top level criteria would include: capacity, injectivity, confinement, risk minimisation and societal acceptance. Maroto-Valoor (2010)


To store something so that it is no longer available. Carbon sequestration involves the removal or storage of carbon dioxide so that it can’t be released into the atmosphere. The term is often regarded as synonymous with storage, but has other confusing meanings and should be avoided in favour of storage. Terrestrial sequestration is the absorption and storage of CO2 by vegetation and soils in terrestrial ecosystems.


Any of a group of fine-grained, laminated sedimentary rocks consisting of silt- and clay-sized particles. Shale is the most abundant of the sedimentary rocks, accounting for roughly 70 percent of this rock type in the crust of the Earth. Shales characteristically consist of at least 30 percent clay minerals and substantial amounts of quartz. These rocks have very low permeability.


is a relative term that can mean different things depending on the context or on the method of study being used. For example, when applied to gas geochemistry it refers to the soil-atmosphere interface (for flux measurements) down to the top of the water table (typically 1-5m, for soil gas measurements). When applied to groundwater chemistry it can refer to the more shallow (potable) aquifers where monitoring can occur, which could be from 10 to 50m depth. Instead when applied to geophysical methods, it could refer from the first 1–5 metres (for a technique like ground penetrating radar), to 10–100m (for methods like electrical resistivity or low-energy source active seismic). Finally another definition may refer to the local geology, whereby anything within the bedrock is considered deep while anything in the overlying unconsolidated sediments is considered shallow - this definition has the potential advantage of being linked to material characteristics (e.g. porosity) but is very site specific.


The natural uptake of CO2 from the atmosphere, typically in soils, forests or the oceans. According to UNFCCC – “Sink” means any process, activity or mechanism which removes a greenhouse gas, an aerosol or a precursor of a greenhouse gas from the atmosphere.


is a European research project about CO2 storage site characterisation, which started in January 2011 and will last 3 years. Central to the Sitechar project is examining the technical, economic and societal requirements for a company to be allowed to store CO2 underground.


At the Statoil Hydro-operated Sleipner fields on the Norwegian continental shelf, carbon dioxide from produced gas is captured and stored in a subsea aquifer. Emissions of more than 10 million tonnes of carbon dioxide to the atmosphere have been avoided since production started in 1996. This is more carbon dioxide than the total number of cars in Norway emit in two years. The Sleipner site is a study area within the ECO2 Project. TechnologyInnovation/NewEnergy/CO2Management/Pages/SleipnerVest.aspx

Soil carbon sequestration

Occurs through direct and indirect fixation of atmospheric CO2. Direct soil carbon sequestration occurs by inorganic chemical reactions that convert CO2 into soil inorganic carbon compounds such as calcium and magnesium carbonates. Direct plant carbon sequestration occurs as plants photosynthesise atmospheric CO2 into plant biomass. Subsequently, some of this plant biomass is indirectly sequestered as soil organic carbon (SOC) during decomposition processes. Worldwide, SOC in the top 1 meter of soil comprises about 3/4 of the earth’s terrestrial carbon.

Soil gas

Gas contained in the space between soil grains.

Solid hydrate

When an excess of CO2 is present in relatively cold ocean water (below 8°C) a solid hydrate can form consisting of six or more water molecules that make a cage around one CO2 molecule.

Solubility trapping

(in CCS) A liquid that can soak up carbon dioxide.

Stable geological formation

 A formation that has not recently been disturbed by tectonic movement.


(in CCS) a process for retaining captured CO2 so that it does not reach the atmosphere.

Storage complex

The storage site and surrounding geological domain which can have an effect on overall storage integrity and security; that is, secondary containment formations. (Art.3 (6) CCS-Directive)

Storage site

An underground rock formation that can store carbon dioxide; commonly this is deep sedimentary and porous rock, where there are tiny spaces between the rock grains for the carbon dioxide.

Stratigraphic trap

A sealed geological container capable of retaining fluids, formed by changes in rock type, structure or facies.

Structural trap

Geological structure capable of retaining hydrocarbons, sealed structurally by a fault or fold.


Geological feature produced by the deformation of the Earth’s crust, such as a fold or a fault; a feature within a rock such as a fracture; or, more generally, the spatial arrangement of rocks.


In CCS terms, the consolidated geological strata beneath the seabed, Storage is usually at a considerable depth of thousands of metres within the strata beneath the bottom of the sea.


carbon dioxide (or any substance) is said to be in a supercritical state when its temperature and pressure are above its critical point. The critical point is the highest temperature and pressure at which it can exist as a gas and liquid in equilibrium. In its supercritical state, a substance shows properties of both liquids and gases, expanding to fill its container like a gas, but with the density of a liquid. The critical point for carbon dioxide occurs at a pressure of 73.8 bar (73 atm) and a temperature of 31.1°C.


Technical Potential

(in CCS) The amount by which it is possible to reduce greenhouse gas emissions by implementing a technology or practice that has reached the demonstration phase.

Transport, CO2

is the process of moving captured CO2 through a pipeline, or by other means (e.g. ship) from its source to a suitable storage site.


A geological structure that physically retains fluids that are lighter than the background fluids, e.g. an inverted cup.

Trapping , Geochemical

Where the CO2 reacts with the in situ fluids and host rock. First dissolves in water (00’s to 000’s of years) becomes denser and sinks down into the formation. Next, chemical reactions between the dissolved CO2 and rocks and minerals form ionic species, so that a fraction of the injected CO2 is converted into solid carbonate minerals (millions of years) (IPCC).

Trapping, Adsorbtion

CO2 is preferentially adsorbed onto coal or organic-rich shales replacing gases such as methane. In these cases, CO2 will remain trapped as along as pressures and temperatures remain stable. These processes would normally take place at shallower depths than CO2 storage in hydrocarbon reservoirs IPCC.

Trapping, Dissolution

CO2 dissolves into surrounding salt water (EBTP/ZEP).

Trapping, Mineral

CO2 rich water sinks to the bottom of the reservoir and reacts to form minerals. (EBTP/ZEP).

Trapping, Physical

where upward migration is prevented by a cap rock, normally clay or shale, above the storage location IPCC

Trapping, Residual

CO2 is trapped in rock pores and cannot move. (EBTP/ZEP).

Trapping, Solubility

the process in which CO2 dissolves into formation waters. The extent of dissolution generally decreases with increasing temperature and salinity, and increases with increasing pressure. The process removes CO2 as a separate buoyant phase.

Triple point

(of CO2) the temperature and pressure where carbon dioxide exists as a gas, liquid and solid simultaneously.



United Nations International Maritime Organization .


United Nations Convention on the Law of the Sea, which was adopted at Montego Bay on 10 December 1982.


A solution that could contain more solute than is presently dissolved in it


United Nations Framework Convention on Climate Change.

Unmineable coal bed

Extremely unlikely to be mined under current or foreseeable economic conditions. A coal bed that is unlikely to ever be mined – because it is too deep or too thin – may be potentially used for CO2 storage. If subsequently mined, the stored CO2 would be released. Enhanced Coal Bed Methane (ECBM) recovery could potentially increase methane production from coals while simultaneously storing CO2. The produced methane would be used
and not released to the atmosphere. (IPCC Geological Storage).

Utsira Formation

The Utsira Formation is a deep saline reservoir 800–1000 metres (2600–3300ft) below the sea floor, comprised of a 200–250 metre thick massive sandstone. It is estimated that the Utsira Formation is capable of storing 600 billion tons of CO2. 3D seismic monitoring of the CO2 injection into the Utsira Formation shows that there is no leakage of the CO2 into other horizons. It is the receiving formation for CO2 injection at Sleipner. tools/projects/sleipner.html


Volatile organic

Any organic compound that participates in atmospheric photochemical compound (VOC) reactions; can be a nationally regulated air pollutant


Water column

a notional column of water above the sediment and upwards to the surface of the sea, lake, river etc. Many aquatic phenomena: chemical, physical and biological are explained by mixing in the water column.


A bored, drilled or driven shaft, or a dug hole, whose depth is greater than the largest surface dimension (USGS)(40 CFR 144.3 and 40 CFR 146.3).

Well injection

The subsurface emplacement of “fluids” through a bored, drilled, or driven “well”, or through a dug well, where the depth of the dug well is greater than the largest surface dimension (USGS)



(The) Zero Emissions Technological Platform.