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(wells) Actions taken to ensure permanent isolation of the fluids and pressures of exposed permeable zones within a well from the surface and from lower pressured zones


Reduction in the degree or intensity of emissions or other pollutants


Chemical or physical take-up of molecules, atoms or ions into the bulk of a solid or liquid, forming either a solution or compound


Activities aiming to document and report avoided CO2 emissions for a project

 Acid gas

Any gas mixture that turns to an acid when dissolved in water (normally refers to H2S + CO2 from sour gas)


A process in which no heat is gained or lost


The adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface

 Aluminosilicate mineral

Natural mineral – such as feldspar, clays, micas, amphiboles – composed of Al2O3 and SiO2 plus other cations


Organic chemical compound containing one or more nitrogens in -NH2, -NH or -N groups


Anhydrous calcium sulphate, its common hydrous form is called gypsum


Hard, compact variety of coal that has a high luster; it has the highest carbon content, the fewest impurities, and the highest calorific content of all types of coal

 Anthropogenic source

Source which is man-made as opposed to natural


Folded geological strata that is convex upwards


American Petroleum Institute; degree API is a measure of oil density


An underground layer of fluid-bearing permeable rock or unconsolidated materials (gravel, sand, or silt) with significant permeability to allow flow

 Assessment unit

(petroleum) A volume of rock within the total petroleum system that contains fields (discovered and undiscovered) which share similar geological traits and socioeconomic factors


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

 Bamako Convention 1991

Bamako Convention on the Ban on the Import into Africa and the Control of Transboundary Movement and Management of Hazardous Wastes within Africa

 Barrier formations

(in CO2 storage) Underground geological layers that hinder the vertical movement of the CO2 plume.


A type of basic igneous rock which contains less than 20% quartz and less than 10% feldspar, where at least 65% of the feldspar is in the form of plagioclase

 Basalt formations

Basaltic rocks such as lava flows that 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 sedimentary strata dipping towards a common axis or centre


Pertaining to the depth of water


Relating to the bottom of a sea or lake or to the organisms that live there

 Bicarbonate ion

The anion formed by dissolving carbon dioxide in water, HCO3-


Biological material derived from living or recently living organisms, usally referring to plants

 Biomass-based CCS

Carbon capture and storage in which the feedstock is biomass

 Bituminous coal

An intermediate rank of coal falling between the extremes of peat and anthracite, and closer to anthracite


(well) Refers to catastrophic failure of a well when the petroleum fluids or water flow unrestricted to the surface

 Bulk CO2

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


Tendency of a fluid or solid to rise through a fluid of higher density


Calcium carbonate


Calcium oxide

 Capillary entry pressure

Additional pressure needed for a liquid or gas to enter a pore and overcome surface tension

 Capillary trapping

Immobilisation of a fraction of in-situ fluids by capillary forces


Rock of very low permeability that acts as an upper seal to prevent fluid flow out of a reservoir


The separation of carbon dioxide from other gases before it is emitted to the atmosphere

 Capture efficiency

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

 Carbon credit

A convertible and transferable instrument that allows an organisation to benefit financially from an emission reduction

 Carbon trading

A market-based approach that allows those with excess emissions to trade that excess for reduced emissions elsewhere


Natural minerals (e.g. calcite, dolomite, siderite, limestone) composed of various anions bonded to a CO32- cation

 Carbonate neutralization

A method for storing carbon in the ocean based upon the reaction of CO2 with a mineral carbonate such as limestone to produce bicarbonate anions and soluble cations


A pipe which is inserted to stabilise the borehole of a well after it is drilled


Coalbed methane


Combined Cycle Gas Turbine


Carbon dioxide Capture and Storage


Kyoto Protocol’s Clean Development Mechanism


In the context of carbon trading, certifying that a project achieves a quantified reduction in emissions over a given period


CO2 Geological Storage; Injection accompanied by storage of CO2 streams in underground geological formations.


A magnesium-iron aluminosilicate sheet silicate clay mineral

 Class “x” well

A regulatory classification for wells used for the injection of fluids into the ground


The system of joints, cleavage planes, or planes of weakness found in coal seams along which the coal fractures

 Closing contour

The lowest structural contour that contains the structure; measurements of both the areal closure and the distance from the apex to the lowest closing contour are typically incorporated in calculations of the estimated hydrocarbon content of a trap


Carbon monoxide


Carbon dioxide

 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 equivalent

A measure used to combine emissions of different greenhouse gases based on their global warming potential

 CO2 plume

Dispersing volume of CO2-rich phase contained in target formation

 CO2 stream

A flow of substances resulting from CO2 capture processes, or which consists of a sufficient fraction of CO2 and sufficiently low concentrations of other substances to meet specifications of streams permitted for long term geological storage


(well) Refers to the cementing and perforating of casing and stimulation to connect a well bore to reservoir


Restriction of the movement of a fluid to a designated volume (e.g. reservoir)

 Continental shelf

The extended perimeter of each continent and associated coastal plain submerged under relatively shallow seas

 Contingency plan

Plan to implement corrective measures if a significant irregularity occurs

 Corrective measure

Measure taken to correct (remediate) significant irregularities or to prevent or stop leakages of CO2 from the storage volume

 Critical point

The highest temperature and pressure at which a substance can exist as a vapour and liquid phase in equilibrium


A mineral: dihydroxide sodium aluminium carbonate

 Deep saline aquifer

A deep underground rock formation composed of permeable materials and containing highly saline fluids

 Deep sea

The sea below 1000m depth

 Demonstration phase

Demonstration phase means that the technology is implemented in a pilot project or on a small scale, but is not yet economically feasible at full scale

 Dense fluid

A gas compressed to a density approaching that of the liquid


(hydrocarbon reservoir) one where production is significantly reduced

 Depleted gas field

Reservoir rock where most of the gas has been extracted from between the grains of rock

 Depleted oil field

Reservoir rock where most of the oil has been extracted from between the grains of rock


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


Dissolved Inorganic Carbon


(geology) The steepest angle of descent of a tilted rock strata or feature relative to a horizontal plane


The amount of water issuing from a spring or in a stream that passes a specific point in a given period of time

 Discordant sequence

(geology) sequence of rock strata that is markedly different from strata above or below


A magnesium-rich carbonate mineral (CaMgCO3), also the corresponding sedimentary rock

 Down-hole log

Record of conditions in a borehole

 Drill cuttings

The solid particles recovered during the drilling of a well

 Drill string

The assembly of drilling rods that leads from the surface to the drilling tool


Fluid flow created in formations by pressure differences arising from borehole operations

 Dry ice

Solid carbon dioxide


European Commission


Enhanced coalbed methane 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


Enhanced coalbed methane production


Enhanced Gas Recovery: the recovery of gas additional to that produced naturally by fluid injection or other means


Enhanced Geothermal Systems


Environmental Impact Assessment

 Emission factor

A normalised measure of GHG emissions in terms of activity, e.g. tonnes of GHG emitted per tonne of fuel consumed

 Emissions credit

A commodity giving its holder the right to emit a certain quantity of GHGs

 Emissions trading

A trading scheme that allows permits for the release of a specified number of tonnes of a pollutant to be sold and bought


Concerning a chemical reaction that absorbs heat, or requires heat to drive it

 Enhanced gas recovery

The recovery of gas additional to that produced naturally, achieved by fluid injection or other means

 Enhanced oil recovery

The recovery of oil additional to that produced naturally, achieved by fluid injection or other means


Enhanced Oil Recovery: the recovery of oil additional to that produced naturally, achieved by fluid injection or other means


Equation of State: a thermodynamic equation which describes the state of matter under a given set of physical conditions


Emissions Trading System, defined in the EU ETS Directive 2003/87/EC amended by Directive 2009/29/EC


European Union

 EU CCS Directive

Directive 2009/31/EC of the European Parliament and of the Council of 23 April 2009 on the geological storage of carbon dioxide


A water soluble rock formed by evaporation from an aqueous solution


Concerning a chemical reaction that releases heat, such as combustion

 Extended reach well

Borehole that is diverted into a more horizontal direction to extend its reach

 Far field

A region located far from a signal source


(geology) A surface at which strata are no longer continuous, but are found displaced

 Fault reactivation

The tendency for a fault to become active, i.e. for movement to occur

 Fault slip

The extent to which a fault has slipped in past times


A group of alumino-silicate minerals (K, Na)AlSi3O8 - CaAl2Si2O8 that makes up much of the Earth’s crust


(reservoir) The injection of a fluid into an underground reservoir


(geology) The bending of sedimentary rock strata from the plane in which they were formed


A body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it

 Formation water

Water that occurs naturally within the pores of rock formations

 Fossil fuel

Oil, gas and coal are fossil fuels, formed over millions of years from the remains of plants and animals (fossils); they are hydrocarbons


Any break in rock along which no significant movement has occurred

 Fugitive emission

Any releases of gases or vapours from anthropogenic activities such as the processing or transportation of gas or petroleum


The Group of Eight (forum of senior offical representatives from France, Germany, Italy, Japan, United Kingdom, United States of America, Canada, Russia)


Process by which a carbon-containing solid fuel is transformed into a carbon- and hydrogen-containing gaseous fuel by reaction with air or oxygen and steam


Global Carbon Capture and Storage Institute

 Geochemical trapping

The retention of injected CO2 by geochemical reactions

 Geological formation

A lithostratigraphic subdivision within a sedimentary succession within which distinct rock layers can be found and mapped

 Geological setting

The geological environment

 Geological time

The time over which geological processes have taken place


The science of the movement of the Earth’s crust an rocks


The earth, its rocks and minerals, and its waters


Concerning heat flowing from deep in the earth


Greenhouse gases: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydroflurocarbons (HFCs), perfluorocarbons (PFCs), and sulphur hexafluoride (SF6)


Implementing Agreement for a Co-operative Programme on Technologies Relating to Greenhouse Gases Derived from Fossil Fuel Use (IEA Greenhouse Gas R&D Programme)


(in CO2 storage) Geological formations where no hydrocarbon production has occured within the potential storage area; (in CO2 capture) New facilities where no previously exists

 Greenhouse gas

Gas in the atmosphere that absorbs and emits infrared radiation emitted by the Earth’s surface, the atmosphere, and clouds; thus, trapping heat within the surface-troposphere system. e.g. water vapour (H2O), carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), ozone (O3), sulfur hexafluoride (SF6), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs)



 Henry’s Law

States that the solubility of a gas in a liquid is proportional to the partial pressure of the gas in contact with the liquid


Higher heating value: the energy released from the combustion of a fuel that includes the latent heat of water

 Host rock

(geology) The rock formation that contains a foreign material


Health, safety and environment


A solid compound containing water molecules combined in a definite ratio together with CO2, CH4 or similar gases as an integral part of the crystal

 Hydraulic unit

Hydraulically connected pore space where pressure communication can be measured by technical means and which is bordered by flow barriers, such as faults, salt domes, lithological boundaries, or by the wedging out or outcropping of the formation.

 Hydrodynamic trap

A geological structure in which fluids are retained by low levels of porosity in the surrounding rocks


Concerning water in the geological environment


Pertaining to the properties of a stationary body of water


The phenomenon of a lagging recovery from deformation or other disturbance


International Energy Agency


International Energy Agency – Greenhouse Gas R&D Programme


Integrated Gasification Combined Cycle: power generation in which hydrocarbons or coal are gasified and the gas is used as a fuel to drive both a gas and a steam turbine


Rock formed when molten rock (magma) has cooled and solidified (crystallised)

 Immature basin

A basin in which the processes leading to oil or gas formation have started but are incomplete


The process of using pressure to force fluids down wells

 Injection well

A well in which fluids are injected rather than produced


A measure of the rate at which a quantity of fluid can be injected into a well

 In-situ mineralisation

A process where minerals are not mined: carbon dioxide is injected in the silicate formation where it reacts with the minerals, forming carbonates and silica


Intergovernmental Panel on Climate Change

 IPCC 2005

IPCC 2005 Special Report on Carbon Dioxide Capture and Storage

 Kyoto Protocol

Protocol to the United Nations Framework Convention on Climate Change, which was adopted at Kyoto on 11 December 1997

 Lateral seal

Geological structure that impedes the movement of fluids horizontally


Life Cycle Assessment


To desolve a substance from a solid


(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column


Lower heating value: energy released from the combustion of a fuel that excludes the latent heat of water

 Lignite/sub-bituminous coal

Relatively young coal of low rank with a relatively high hydrogen and oxygen content


A sedimentary rock made mostly of the mineral calcite (calcium carbonate), usually formed from shells of dead organisms


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


Liquified Natural Gas


(well) Records taken during or after the drilling of a well

 London Convention

International convention on the prevention of marine pollution by dumping of wastes and other matter, which was adopted at London, Mexico City, Moscow and Washington on 29 December 1972

 London Protocol

Protocol to the London Convention, adopted in London on 2 November 1996 but which had not entered into force at the time of writing


Liquified Petroleum Gas


Term used for silicate minerals, magmas, and rocks, which arerelatively high in the heavier elements

 Magmatic activity

The flow of magma (lava)


(geology) The process of changing with time; e.g. the alteration of peat into lignite, then into sub-bituminous and bituminous coal, and then into anthracite

 Mature sedimentary basins

Geological provinces formed by the deposition of particulate matter under water when the deposits have matured into hydrocarbon reserves


A non-SI unit of permeability, milli Darcy, and approximately equal to 1μm2

 Medium-gravity oil

Oil with a density of between about 850 and 925kg/m3 (between 20 and 30 API)


Rocks that have been altered by heat and/or pressure


Class of silicate minerals with internal sheet like structure


Small-scale seismic tremors


The movement of fluids in reservoir rocks

 Mineral trap

A geological structure in which fluids are retained by the reaction of the fluid to form a stable mineral


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

 Miscible displacement

Injection process that introduces miscible gases into the reservoir, thereby maintaining reservoir pressure and improving oil displacement


The process of reducing the impact of any failure


Measurement and surveillance activities necessary for ensuring safe and reliable operation of a CGS project (storage integrity), and for estimating emission reductions

 Monte Carlo

A modelling technique in which the statistical properties of outcomes are tested by random inputs


In line with the EU ETS Directive, the Commission has adopted guidelines for the monitoring and reporting of greenhouse gas emissions, known as the "MRG"


Million tonnes


A very fine-grained sedimentary rock formed from mud






Megawatt thermal

 Natural analogue

A natural occurrence that mirrors in most essential elements an intended or actual human activity

 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 in which fluids are retained by natural processes

 Navier-Stokes equations

The general equations describing the flow of fluids


The region located close to a signal source


Natural Gas Combined Cycle: natural-gas-fired power plant with gas and steam turbines

 Observation well

A well installed to permit the observation of subsurface conditions


Convention for the Protection of the Marine Environment of the North-East Atlantic, which was adopted at Paris on 22 September 1992


The point at which a particular rock formation reaches the earth’s surface


Rocks and sediments above any particular stratum


Pressure created in a reservoir that exceeds the pressure inherent at the reservoir depth


The loss of one or more electrons by an atom, molecule, or ion

 Partial pressure

The pressure that would be exerted by a particular gas in a mixture of gases if the other gases were not present, e.g. pCO2 ishe partial pressure of CO2


Pulverized coal: usually used in connection with boilers fed with finely ground coal


Ability to flow or transmit fluids through a porous solid such as rock


A geological age between 290 and 248 million years ago


Perfluorated hydrocarbons

 Point source

An emission source that is confined to an identifiable location/region

 Pore space

Space between rock or sediment grains that can contain fluids


Elastic behaviour of porous media


Measure for the amount of pore space in a rock


Period after transfer of responsibility to the competent authority

 Post-combustion capture

The capture of carbon dioxide after combustion

 Pre-combustion capture

The capture of carbon dioxide following the processing of the fuel before combustion

 Preventive measure

Measure taken to prevent hazards from occurring; either by reducing the probability that it occurs or by minimising potential damages or negative consequences


(coal) Quality criterion for coal


Reduction-oxidisation reaction


The gain of one or more electrons by an atom, molecule, or ion


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

 Residual saturation

The fraction of the injected CO2 that is trapped in pores by capillary forces


Concept that denotes the product of the probability of a hazard and the subsequent consequence of the associated event

 Risk assessment

A process intended to calculate or estimate the risk to a given target, part of a risk management system

 Saline formation

Underground rock where saline water occupies the tiny spaces between the grains of rock

 Saline groundwater

Groundwater in which salts are dissolved


Sand that has turned into a rock due to geological processes

 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


Boundary between the free water and the top of the seabottom sediment


An impermeable rock that forms a barrier above and around a reservoir such that fluids are held in the reservoir

 Secondary recovery

(oil) Recovery of oil by artificial means, after the natural production mechanisms like overpressure have ceased

 Sedimentary basin

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

 Seismic profile

A two-dimensional seismic image of the subsurface

 Seismic technique

Measurement of the properties of rocks by the speed of sound waves generated artificially or naturally


The episodic occurrence of natural or man-induced earthquakes


Clay that has changed into a rock due to geological processes

 Shale formation

Is characterised by thin horizontal layers of rock with very low permeability, especially in the vertical direction; it is the most common sedimentary rock

 Significant irregularity

Any irregularity in the injection or storage operation or in the condition of the storage volume itself, which implies the risk of a leakage or risk to the environment or human health


(CO2) The natural uptake of CO2 from the atmosphere, typically in soils, forests or the oceans

 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 water molecules that make a cage around one CO2  molecule

 Solubility trapping

A process in which fluids are retained by dissolution in liquids naturally present

 Sour gas

Natural gas containing significant quantities of acid gases like H2S and CO2


Any process, activity or mechanism that releases a greenhouse gas, an aerosol, or a precursor thereof into the atmosphere


The determination of the number of species into which a single species may evolve over time

 Spill point

The structurally lowest point in a structural trap that can retain fluids lighter than background fluids


(well) The enhancement of the ability to inject fluids into, or recover fluids from, a well


(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere

 Storage capacity

The accumulated mass of CO2 that can be stored environmentally safely, i.e., without causing leakage of CO2 or native reservoir fluids or triggering geologic activity that has a negative impact on human health or the environment

 Storage complex

The storage site and surrounding geological domain which can have an effect on overall storage integrity and security; that is, a primary containment system and any secondary containment system.

 Storage site

Defined volume used for CO2 geological storage including the storage complex, overburden and the associated storage and injection facilities


The order and relative position of geological strata

 Stratigraphic column

A column showing the sequence of different geological strata

 Stratigraphic trap

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

 Structural trap

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


(geology) 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

 Structure contour map

Map showing the contours of geological structures

 Sub-bituminous coal

Coal of a rank between lignite and bituminous coal


(CO2) Conditions where carbon dioxide has some characteristics of a gas and some of a liquid


Synthesis gas: gas mixture that contains varying amounts of carbon monoxide and hydrogen

 Tectonically active area

Area of the Earth where deformation is presently causing structural changes


Geological age from about 65 to 2 million years ago

 Tertiary recovery

Oil generated by a method other than pressure release or depletion (primary), or the injection of water (secondary)


The ocean phenomenon characterised by a sharp change in temperature with depth


The vertical overturning of water masses due to seasonal heating, evaporation, and cooling


A chemical compound or isotope added in small quantities to trace flow patterns

 Transfer of responsibility

Transfer of all rights and obligations associated with a storage site to a designated authority; will normally be granted when the obligations in the site closure permit has been met with an adequate level of confidence


(geology) A geological structure that physically retains fluids that are lighter than the background fluids, e.g. a convex fold


(CO2) Containment or immobilisation of CO2, there are four main trapping mechanisms: structural or stratigraphic trapping; residual CO2 trapping (capillary trapping) by capillary forces; solubility trapping by dissolution of CO2 in resident formation fluids forming a non-buoyant fluid; and mineral trapping where CO2 is absorbed by solid minerals present in the storage volume

 Triple point

The temperature and pressure where carbon dioxide exists as a gas, liquid and solid simultaneously

 Ultramafic rocks

An igneous rock consisting almost entirely of iron- and magnesium-rich minerals with a silica content typically less than 45%


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


United Nations Framework Convention on Climate Change, which was adopted at New York on 9 May 1992


Extremely unlikely to be mined under current or foreseeable economic conditions


Inclining upwards following a structural contour of strata

 Upper ocean

The ocean above 1000m depth


Universal Transverse Mercator geographic coordinate system

 Vadose zone

Near surface layer of aeration above the water table (where ambient air infiltrates soil)


(in the context of CDM) The process of the independent evaluation of a project by a designated operational entity on the basis of set requirements


The exchange of gases dissolved in sea-water with the atmosphere, or genrally, gas exchange between an animal or a man-made space and the environment


(CO2 storage) The proof, to a standard still to be decided, of the CO2 storage using monitoring results; (in the context of CDM) The independent review by a designated operational entity of monitored reductions in anthropogenic emissions

 Vertical seal

Geological structure impeding the movement of fluids vertically (caprock)

 Viscous fingering

Flow phenomenon arising from the flow of two largely immiscible fluids through a porous medium

 Water column

Vertically continuous mass of water from the surface to the bottom sediments of a water body


Manmade hole drilled into the earth to produce liquids or gases, or to allow the injection of fluids

 Well with multiple completions

Well drilled with multiple branching holes and more than one hole being made ready for use


The physical hole that makes up the well, it can be cased, open, or a combination of both; open means open for fluid migration laterally between the wellbore and surrounding formations; cased means closing of the wellbore to avoid such migration

 Well-bore annulus

The annulus between the rock and the well casing

 Wellhead pressure

Pressure measured on surface at the top of the well


Surface with properties allowing water to contact the surface intimately


European Technology Platform for Zero Emission Fossil Fuel Power Plants

 Zero-carbon energy carrier

Carbon-free energy carrier, typically electricity or hydrogen