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Glossary

 Abandonment

(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

 Abatement

Reduction in the degree or intensity of emissions or other pollutants

 Absorption

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

 Accounting

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)

 Adiabatic

A process in which no heat is gained or lost

 Adsorption

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

 Amine

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

 Anhydrite

Anhydrous calcium sulphate, its common hydrous form is called gypsum

 Anthracite

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

 Anticline

Folded geological strata that is convex upwards

 API

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

 Aquifer

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

 Atmosphere

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.

 Basalt

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

 Basin

A geological region with sedimentary strata dipping towards a common axis or centre

 Bathymetric

Pertaining to the depth of water

 Benthic

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-

 Biomass

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

 Blow-out

(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%

 Buoyancy

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

 CaCO3

Calcium carbonate

 CaO

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

 Caprock

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

 Capture

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

 Carbonate

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

 Casing

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

 CBM

Coalbed methane

 CCGT

Combined Cycle Gas Turbine

 CCS

Carbon dioxide Capture and Storage

 CDM

Kyoto Protocol’s Clean Development Mechanism

 Certification

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

 CGS

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

 Chlorite

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

 Cleat

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

 CO

Carbon monoxide

 CO2

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

 Completion

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

 Containment

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

 Dawsonite

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

 Depleted

(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

 Diagenesis

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

 DIC

Dissolved Inorganic Carbon

 Dip

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

 Discharge

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

 Dolomite

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

 Drive

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

 Dry ice

Solid carbon dioxide

 EC

European Commission

 ECBM

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

 ECBMP

Enhanced coalbed methane production

 EGR

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

 EGS

Enhanced Geothermal Systems

 EIA

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

 Endothermic

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

 EOR

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

 EOS

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

 ETS

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

 EU

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

 Evaporite

A water soluble rock formed by evaporation from an aqueous solution

 Exothermic

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

 Fault

(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

 Feldspar

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

 Flood

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

 Folding

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

 Formation

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

 Fracture

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

 G8

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

 Gasification

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

 GCCSI

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

 Geomechanics

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

 Geosphere

The earth, its rocks and minerals, and its waters

 Geothermal

Concerning heat flowing from deep in the earth

 GHG

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

 GHG IA

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

 Greenfields

(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)

 H2

Hydrogen

 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

 HHV

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

 HSE

Health, safety and environment

 Hydrate

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

 Hydrogeological

Concerning water in the geological environment

 Hydrostatic

Pertaining to the properties of a stationary body of water

 Hysteresis

The phenomenon of a lagging recovery from deformation or other disturbance

 IEA

International Energy Agency

 IEA GHG

International Energy Agency – Greenhouse Gas R&D Programme

 IGCC

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

 Igneous

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

 Injection

The process of using pressure to force fluids down wells

 Injection well

A well in which fluids are injected rather than produced

 Injectivity

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

 IPCC

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

 LCA

Life Cycle Assessment

 Leach

To desolve a substance from a solid

 Leakage

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

 LHV

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

 Limestone

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

 Lithology

The nature and composition of rocks

 Lithosphere

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

 LNG

Liquified Natural Gas

 Log

(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

 LPG

Liquified Petroleum Gas

 Mafic

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

 Magmatic activity

The flow of magma (lava)

 Maturation

(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

 mD

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)

 Metamorphic

Rocks that have been altered by heat and/or pressure

 Mica

Class of silicate minerals with internal sheet like structure

 Microseismicity

Small-scale seismic tremors

 Migration

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

 Mineralisation

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

 Mitigation

The process of reducing the impact of any failure

 Monitoring

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

 MRG

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"

 Mt

Million tonnes

 Mudstone

A very fine-grained sedimentary rock formed from mud

 MW

Megawatt

 MWh

Megawatt-hour

 MWth

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

 Near-field

The region located close to a signal source

 NGCC

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

 OSPAR

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

 Outcrop

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

 Overburden

Rocks and sediments above any particular stratum

 Overpressure

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

 Oxidation

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

 PC

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

 Permeability

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

 Permian

A geological age between 290 and 248 million years ago

 PFC

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

 Poroelastic

Elastic behaviour of porous media

 Porosity

Measure for the amount of pore space in a rock

 Post-closure

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

 Rank

(coal) Quality criterion for coal

 Redox

Reduction-oxidisation reaction

 Reduction

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

 Reservoir

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

 Risk

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

 Sandstone

Sand that has turned into a rock due to geological processes

 Saturated zone

Part of the subsurface that is totally saturated with groundwater

 Scenario

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

 Seabed

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

 Seal

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

 Seismicity

The episodic occurrence of natural or man-induced earthquakes

 Shale

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

 Sink

(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

 Source

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

 Speciation

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

 Stimulation

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

 Storage

(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

 Stratigraphic

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

 Structure

(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

 Supercritical

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

 Syngas

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

 Tertiary

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)

 Thermocline

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

 Thermohaline

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

 Tracer

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

 Trap

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

 Trapping

(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%

 Under-saturated

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

 UNFCCC

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

 Unminable

Extremely unlikely to be mined under current or foreseeable economic conditions

 Updip

Inclining upwards following a structural contour of strata

 Upper ocean

The ocean above 1000m depth

 UTM

Universal Transverse Mercator geographic coordinate system

 Vadose zone

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

 Validation

(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

 Ventilation

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

 Verification

(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

 Well

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

 Wellbore

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

 Wettability

Surface with properties allowing water to contact the surface intimately

 ZEP

European Technology Platform for Zero Emission Fossil Fuel Power Plants

 Zero-carbon energy carrier

Carbon-free energy carrier, typically electricity or hydrogen