1. INTRODUCTION

It is widely accepted that prolific burning of fossil fuels has raised the amount of CO2Carbon dioxide in the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) to levels at which it is contributing to climate change and that de-carbonising energy is necessary to avert catastrophic and irreversible change. Carbon CaptureThe separation of carbon dioxide from other gases before it is emitted to the atmosphere and Storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere (CCSCarbon dioxide Capture and Storage) is a technology that could contribute significantly to reduced CO2Carbon dioxide emissions to the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%). It works by removing CO2Carbon dioxide from the pre- or post-combustion exhaust gas of power stations and other industrial processes and injecting the CO2Carbon dioxide into underground geological reservoirs of porous rock for permanent storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere. While not eliminating society's dependence on fossil fuels, it provides a bridging solution to mitigate the problem while renewable energy Sources are developed to large-scale implementation and the acceptability of nuclear power into the future is resolved.

The selection and characterisation of potential CO2Carbon dioxide storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere sites are probably the most important steps for ensuring the safety and integrity of a CO2Carbon dioxide storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere project and are essential in developing a CCSCarbon dioxide Capture and Storage project. In essence, a site selection process should demonstrate that the site has: sufficient capacity to store the expected CO2Carbon dioxide volume; sufficient injectivityA measure of the rate at which a quantity of fluid can be injected into a well for the expected rate of CO2Carbon dioxide captureThe separation of carbon dioxide from other gases before it is emitted to the atmosphere and supply; and sufficient containmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) to store safely the injected CO2Carbon dioxide for the period of time required by the regulatory authority, so as not to pose unacceptable Risks to the environment, human health or other uses of the subsurface.

Guidelines have been published by several bodies on the necessary steps and process involved in selecting and managing a storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere site within whatever regulatory environment applies (WRI, 20082008 - WRIGuidelines for CCSsee more; CO2CRC, 20082008 - CO2CRCStorage Capacity Estimation, Site Selection and Characterisation for CO2 Storage Projectssee more; NETL, 2010a2010 - NETLBest practices for: Site screening, site selection, and initial characterization for storage of CO2 in deep geologic formationssee more; NETL, 2010b2010 - NETLBest practices for: Geologic storage formation classification: Understanding its importance and impacts on CCS opportunities in the United Statessee more). It is not the purpose or intention of this report to repeat those, but rather to focus in detail on geoscience aspects of site selection.

Types of storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) sites

There are three main types of reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids for geological storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere of carbon dioxide as a fluid: depleted(hydrocarbon reservoir) one where production is significantly reduced oil and gas fields, saline aquifers and coal beds. Research is also being directed at storing CO2Carbon dioxide by forming solid carbonateNatural minerals (e.g. calcite, dolomite, siderite, limestone) composed of various anions bonded to a CO32- cation minerals by combining CO2Carbon dioxide with reactive rocks with high Fe, Mg and Ca content, such as maficTerm used for silicate minerals, magmas, and rocks, which arerelatively high in the heavier elements and ultramafic igneousRock formed when molten rock (magma) has cooled and solidified (crystallised) rocks - this latter form of storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere is not considered in this report.

A considerable amount of understanding, experience and technology developed by oil and gas operations is directly applicable to storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere site characterisation and selection. CO2Carbon dioxide can 'replace' oil and gas in fields that have been depleted(hydrocarbon reservoir) one where production is significantly reduced, or it can be used to prolong oil or gas production from fields that are still active. Enhanced Oil RecoveryThe recovery of oil additional to that produced naturally, achieved by fluid injection or other means (EOREnhanced Oil Recovery: the recovery of oil additional to that produced naturally, achieved by fluid injection or other means) and Enhanced Gas RecoveryThe recovery of gas additional to that produced naturally, achieved by fluid injection or other means (EGREnhanced Gas Recovery: the recovery of gas additional to that produced naturally by fluid injection or other means) are processes in which CO2Carbon dioxide is injected into a reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids to increase the amount of hydrocarbons extracted, thus providing an economic benefit whilst also potentially storing CO2Carbon dioxide. The main requirement is to ensure that injected CO2Carbon dioxide is not produced with the oil or gas and the EOREnhanced Oil Recovery: the recovery of oil additional to that produced naturally, achieved by fluid injection or other means/EGREnhanced Gas Recovery: the recovery of gas additional to that produced naturally by fluid injection or other means project becomes a CO2Carbon dioxide storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere project. Depleted(hydrocarbon reservoir) one where production is significantly reduced oil and gas fields have the obvious attraction as storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere sites that containmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) at the site has already been demonstrated by the retention of hydrocarbons for millions of years. It is important to ensure, however, that extraction of the hydrocarbons has not damaged the integrity of the reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids or sealAn impermeable rock that forms a barrier above and around a reservoir such that fluids are held in the reservoir by pressure reductionThe gain of one or more electrons by an atom, molecule, or ion and that extraction Wells do not provide potential leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column pathways for CO2Carbon dioxide. Another major advantage of depleted(hydrocarbon reservoir) one where production is significantly reduced Reservoirs over saline Aquifers is that there will be large amounts of geological and engineering data already available for site characterisation.

Saline Aquifers are sedimentary rock units in which pore spaceSpace between rock or sediment grains that can contain fluids is saturated with saline water that is unsuitable for consumption or irrigation. Such units are widely distributed and can be of very large volume and extent. They therefore have the potential to provide large storage capacityThe 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 in areas without depleted(hydrocarbon reservoir) one where production is significantly reduced hydrocarbon Reservoirs. However, because they have not previously had an economic or resource value, they are generally much less-wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injection of fluids understood than hydrocarbon Reservoirs and so assessment of their CO2Carbon dioxide storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere potential carries more uncertainty regarding containmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) security and fluid flow properties.

Carbon dioxide storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere in coal beds is through adsorptionThe adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface onto the coal surfaces rather than filling of pore spaceSpace between rock or sediment grains that can contain fluids. CO2Carbon dioxide is preferentially adsorbed and thus displaces methane (CH₄) from the coal. As with EOREnhanced Oil Recovery: the recovery of oil additional to that produced naturally, achieved by fluid injection or other means, this process can be used to produce coal bed methane and so CO2Carbon dioxide storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere can be combined with hydrocarbon production. In fact, as methane has a higher greenhouse effect than CO2Carbon dioxide, any CO2Carbon dioxide coal storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere projects must include methane production and use, to avoid emission to the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) and result in greenhouse gasGas 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) emission reductionThe gain of one or more electrons by an atom, molecule, or ion.

Trapping(CO2Carbon dioxide) ContainmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) or immobilisation of CO2Carbon dioxide, there are four main trapping mechanisms: structural or stratigraphicThe order and relative position of geological strata trapping; residual CO2Carbon dioxide trapping (capillary trappingImmobilisation of a fraction of in-situ fluids by capillary forces) by capillary forces; solubility trappingA process in which fluids are retained by dissolution in liquids naturally present by dissolution of CO2Carbon dioxide in resident formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it fluids forming a non-buoyant fluid; and mineral trapping where CO2Carbon dioxide is absorbed by solid minerals present in the storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) volume mechanisms

For CO2Carbon dioxide storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere involving partial filling of pore spaceSpace between rock or sediment grains that can contain fluids, it is necessary to inject and store CO2Carbon dioxide in its dense supercritical(CO2) Conditions where carbon dioxide has some characteristics of a gas and some of a liquid form, in order to maximise use of the available porosityMeasure for the amount of pore space in a rock. The critical pointThe highest temperature and pressure at which a substance can exist as a vapour and liquid phase in equilibrium for CO2Carbon dioxide is at 31.1°C and 7.38 MPa; this equates to a depth of approximately 800 m at typical crustal temperatures.

The CO2Carbon dioxide 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 mechanisms include:

• physical trapping(CO2Carbon dioxide) ContainmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) or immobilisation of CO2Carbon dioxide, there are four main trapping mechanisms: structural or stratigraphicThe order and relative position of geological strata trapping; residual CO2Carbon dioxide trapping (capillary trappingImmobilisation of a fraction of in-situ fluids by capillary forces) by capillary forces; solubility trappingA process in which fluids are retained by dissolution in liquids naturally present by dissolution of CO2Carbon dioxide in resident formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it fluids forming a non-buoyant fluid; and mineral trapping where CO2Carbon dioxide is absorbed by solid minerals present in the storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) volume in structural and stratigraphicThe order and relative position of geological strata traps, in which the CO2Carbon dioxide is contained in closures produced by the geometrical arrangement of reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids and sealAn impermeable rock that forms a barrier above and around a reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids such that fluids are held in the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids rocks and faults;
• residual trapping(CO2Carbon dioxide) ContainmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) or immobilisation of CO2Carbon dioxide, there are four main trapping mechanisms: structural or stratigraphicThe order and relative position of geological strata trapping; residual CO2Carbon dioxide trapping (capillary trappingImmobilisation of a fraction of in-situ fluids by capillary forces) by capillary forces; solubility trappingA process in which fluids are retained by dissolution in liquids naturally present by dissolution of CO2Carbon dioxide in resident formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it fluids forming a non-buoyant fluid; and mineral trapping where CO2Carbon dioxide is absorbed by solid minerals present in the storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) volume, in which some portion of migrating CO2Carbon dioxide remains trapped in pore spaces by capillary forces;
• solubility trapping(CO2Carbon dioxide) ContainmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) or immobilisation of CO2Carbon dioxide, there are four main trapping mechanisms: structural or stratigraphicThe order and relative position of geological strata trapping; residual CO2Carbon dioxide trapping (capillary trappingImmobilisation of a fraction of in-situ fluids by capillary forces) by capillary forces; solubility trappingA process in which fluids are retained by dissolution in liquids naturally present by dissolution of CO2Carbon dioxide in resident formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it fluids forming a non-buoyant fluid; and mineral trapping where CO2Carbon dioxide is absorbed by solid minerals present in the storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) volume, in which some portion of the CO2Carbon dioxide dissolves into the formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it waterWater that occurs naturally within the pores of rock formations;
• Hydrodynamic Trapping(CO2Carbon dioxide) ContainmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) or immobilisation of CO2Carbon dioxide, there are four main trapping mechanisms: structural or stratigraphicThe order and relative position of geological strata trapping; residual CO2Carbon dioxide trapping (capillary trappingImmobilisation of a fraction of in-situ fluids by capillary forces) by capillary forces; solubility trappingA process in which fluids are retained by dissolution in liquids naturally present by dissolution of CO2Carbon dioxide in resident formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it fluids forming a non-buoyant fluid; and mineral trapping where CO2Carbon dioxide is absorbed by solid minerals present in the storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) volume, in which, although the dissolved and free CO2Carbon dioxide migrates with formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it waterWater that occurs naturally within the pores of rock formations through the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids, very long residence times mean it is effectively stored permanently;
• mineral trapping(CO2Carbon dioxide) ContainmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) or immobilisation of CO2Carbon dioxide, there are four main trapping mechanisms: structural or stratigraphicThe order and relative position of geological strata trapping; residual CO2Carbon dioxide trapping (capillary trappingImmobilisation of a fraction of in-situ fluids by capillary forces) by capillary forces; solubility trappingA process in which fluids are retained by dissolution in liquids naturally present by dissolution of CO2Carbon dioxide in resident formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it fluids forming a non-buoyant fluid; and mineral trapping where CO2Carbon dioxide is absorbed by solid minerals present in the storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) volume, in which the CO2Carbon dioxide precipitates as new carbonateNatural minerals (e.g. calcite, dolomite, siderite, limestone) composed of various anions bonded to a CO32- cation minerals and so is permanently stored with high security;
• adsorptionThe adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface trapping(CO2Carbon dioxide) ContainmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) or immobilisation of CO2Carbon dioxide, there are four main trapping mechanisms: structural or stratigraphicThe order and relative position of geological strata trapping; residual CO2Carbon dioxide trapping (capillary trappingImmobilisation of a fraction of in-situ fluids by capillary forces) by capillary forces; solubility trappingA process in which fluids are retained by dissolution in liquids naturally present by dissolution of CO2Carbon dioxide in resident formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it fluids forming a non-buoyant fluid; and mineral trapping where CO2Carbon dioxide is absorbed by solid minerals present in the storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) volume, in which gaseous CO2Carbon dioxide adsorbs onto the surface of coal.

Estimating the volumes and proportions of CO2Carbon dioxide that would be trapped by each of these mechanisms is a key part of a site characterisation. Increased understanding of 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 mechanisms is an important area for scientific research.

Site selection

The first stage of a site selection process for CO2Carbon dioxide storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere is a screening of national or regional geology to identify large areas of potentially suitable sedimentary basins. Basins can be assessed and ranked using criteria such as size, depth, stratigraphy (reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids-sealAn impermeable rock that forms a barrier above and around a reservoir such that fluids are held in the reservoir pairs or potentially injectable coal seams), seismicityThe episodic occurrence of natural or man-induced earthquakes, geothermalConcerning heat flowing from deep in the earth characteristics, accessibility, proximity to CO2Carbon dioxide Sources etc. BasinA geological region with sedimentary strata dipping towards a common axis or centre identified as having potentially suitable assets for CO2Carbon dioxide storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere can then be assessed at basinA geological region with sedimentary strata dipping towards a common axis or centre and sub-basinA geological region with sedimentary strata dipping towards a common axis or centre scale to locate possible closures and traps, the distribution of reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids-sealAn impermeable rock that forms a barrier above and around a reservoir such that fluids are held in the reservoir pairs at suitable depths, or coal seams, using existing data such as geological maps, seismic surveys and wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injection of fluids data.

Prospective storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere sites can be ranked for the following factors:

• Storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) CapacityThe accumulated mass of CO2Carbon dioxide that can be stored environmentally safely, i.e., without causing leakage(in CO2Carbon dioxide storage) The escape of injected fluid from the storage formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it to the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) or water column of CO2Carbon dioxide or native reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids fluids or triggering geologic activity that has a negative impact on human health or the environment. A simple estimate can be made of storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) capacityThe accumulated mass of CO2Carbon dioxide that can be stored environmentally safely, i.e., without causing leakage(in CO2Carbon dioxide storage) The escape of injected fluid from the storage formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it to the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) or water column of CO2Carbon dioxide or native reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids fluids or triggering geologic activity that has a negative impact on human health or the environment from the area of the identified trap(geology) A geological structure(geology) Geological feature produced by the deformation of the Earth’s crust, such as a fold or a fault(geology) A surface at which strata are no longer continuous, but are found displaced; a feature within a rock such as a fractureAny break in rock along which no significant movement has occurred; or, more generally, the spatial arrangement of rocks that physically retains fluids that are lighter than the background fluids, e.g. a convex fold, thickness of the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids below the critical depth and the porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock, and this compared to the likely CO2Carbon dioxide supply that the site may need to accommodate. Not all of the total pore spaceSpace between rock or sediment grains that can contain fluids in the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids can be filled with CO2Carbon dioxide and key parameter in capacity estimates is the efficiency or utilisation factor, the fraction of the pore volume that can be occupied by or will retain injected CO2Carbon dioxide. This is a function of the fluid already present in the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids, pore size and shape, grain mineralogy and reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids heterogeneity at all scales. Efficiency factors can vary widely from site to site and have a major effect on capacity calculations. Values used are typically around 40 % for depleted(hydrocarbon reservoir) one where production is significantly reduced gas fields, and range 0.1 - 6 % for saline aquifers; establishing a reliable value for a site before injectionThe process of using pressure to force fluids down wells of CO2Carbon dioxide begins is clearly important and a challenge for future research. The efficiency factor can be maximised by careful injectionThe process of using pressure to force fluids down wells strategy and wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injectionThe process of using pressure to force fluids down wells of fluids planning.
• InjectivityA measure of the rate at which a quantity of fluid can be injected into a well Potential. ReservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids characteristics, such as permeabilityAbility to flow or transmit fluids through a porous solid such as rock, porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and pressure will control the rate at which CO2Carbon dioxide can be injected into the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids. In practise, injectivityA measure of the rate at which a quantity of fluid can be injected into a well can be increased by extending the length of WellboreThe physical hole that makes up the wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injectionThe process of using pressure to force fluids down wells of fluids, it can be cased, open, or a combination of both; open means open for fluid migrationThe movement of fluids in reservoir rocks laterally between the wellbore and surrounding formations; cased means closing of the wellbore to avoid such migrationThe movement of fluids in reservoir rocks within the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids by drilling horizontal wells and/or by increasing the number of wells.
• ContainmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir). For a sealAn impermeable rock that forms a barrier above and around a reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids such that fluids are held in the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids/caprockRock of very low permeability that acts as an upper seal to prevent fluid flow out of a reservoir to be effective for storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%), it must be laterally continuous and sufficiently thick over the proposed injectionThe process of using pressure to force fluids down wells reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids, with low vertical permeabilityAbility to flow or transmit fluids through a porous solid such as rock and high capillary entry pressureAdditional pressure needed for a liquid or gas to enter a pore and overcome surface tension. An effective sealAn impermeable rock that forms a barrier above and around a reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids such that fluids are held in the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids can be demonstrated by a pressure or salinity differential, or a history of trapping(CO2Carbon dioxide) ContainmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) or immobilisation of CO2Carbon dioxide, there are four main trapping mechanisms: structural or stratigraphicThe order and relative position of geological strata trapping; residual CO2Carbon dioxide trapping (capillary trappingImmobilisation of a fraction of in-situ fluids by capillary forces) by capillary forces; solubility trappingA process in which fluids are retained by dissolution in liquids naturally present by dissolution of CO2Carbon dioxide in resident formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it fluids forming a non-buoyant fluid; and mineral trapping where CO2Carbon dioxide is absorbed by solid minerals present in the storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) volume oil or gas. The size and spacing of faulting is also a factor, but it is particularly important to assess whether faults are likely to be sealing or migrationThe movement of fluids in reservoir rocks pathways. The migrationThe movement of fluids in reservoir rocks distance over which CO2Carbon dioxide can travel in the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids will affect the probability of the more secure trapping(CO2Carbon dioxide) ContainmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) or immobilisation of CO2Carbon dioxide, there are four main trapping mechanisms: structural or stratigraphicThe order and relative position of geological strata trapping; residual CO2Carbon dioxide trapping (capillary trappingImmobilisation of a fraction of in-situ fluids by capillary forces) by capillary forces; solubility trappingA process in which fluids are retained by dissolution in liquids naturally present by dissolution of CO2Carbon dioxide in resident formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it fluids forming a non-buoyant fluid; and mineral trapping where CO2Carbon dioxide is absorbed by solid minerals present in the storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) volume mechanisms: residual, hydrodynamic or mineralisationIs a natural form of geologically storing CO2Carbon dioxide  by the very slow reaction between CO2Carbon dioxide  and naturally occurring minerals, such as magnesium silicate, to form the corresponding mineral carbonateNatural minerals (e.g. calcite, dolomite, siderite, limestone) composed of various anions bonded to a CO32- cation.
  
  It is also important to ensure that any existing wells or other artificial breech of the sealAn impermeable rock that forms a barrier above and around a reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids such that fluids are held in the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids will also trap(geology) A geological structure(geology) Geological feature produced by the deformation of the Earth’s crust, such as a fold or a fault(geology) A surface at which strata are no longer continuous, but are found displaced; a feature within a rock such as a fractureAny break in rock along which no significant movement has occurred; or, more generally, the spatial arrangement of rocks that physically retains fluids that are lighter than the background fluids, e.g. a convex fold CO2Carbon dioxide and not provide an escape pathway.
• Site Logistics. Economic and logistical factors will cotrol whether a geologically suitable storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) site can actually be used. Excessively deep wells or long pipelines may make a site uneconomical. On the other hand, clusters of CO2Carbon dioxide sources sharing pipeline and storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) site facilities can make a project more economical. Cooperation among projects at a regional scale will be required to benefit from shared facilities and avoid problems from using the same storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) complex.
• Existing Natural Resources. Competing use of the same underground space, or sterilisation of alternative underground resources that could potentially be compromised by CO2Carbon dioxide storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%), such as oil and gas, mineable coal, potable water, a geothermalConcerning heat flowing from deep in the earth energy sourceAny process, activity or mechanism that releases a greenhouse gasGas in the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) that absorbs and emits infrared radiation emitted by the Earth’s surface, the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%), and clouds; thus, trapping heat within the surface-troposphere system. e.g. water vapour (H2O), carbon dioxide (CO2Carbon dioxide), nitrous oxide (N2O), methane (CH4), ozone (O3), sulfur hexafluoride (SF6), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs), an aerosol, or a precursor thereof into the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%), may require national or regional policies on relative importance of the conflicting interests. Proximity to population centres, national parks or other protected sites, could limit surface operations, either because of legislation or because of negative public reaction.

A key consideration in any project is the selection of the stage to begin the outreach process to best avoid delays caused by negative reaction from communities around potential locations for CO2Carbon dioxide storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere. General consensus from studies and experience seems to be that early is better, to open lines of communication and develop community understanding before fear of the unknown or manipulation by alternative agendas get embedded.

Once a potential storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere site has been identified by the basinA geological region with sedimentary strata dipping towards a common axis or centre-scale assessment described above, it has to be evaluated through a detailed site characterisation, to add quantitative confidence that the site will geologically store the required quantity of CO2Carbon dioxide to the level of security and for the period required by the regulatory authority. The geoscience aspects of a detailed site characterisation as wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injection of fluids as the economic aspects are described in the following chapters of this report, which comprise best practice recommendations from international studies and working groups in CO2Carbon dioxide storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere site selection. In addition, key references are listed for societal aspects:

• Chapter 2 - Geological characterisation of the site - This chapter describes the creation of a geological model with which to assess the volume, injectivityA measure of the rate at which a quantity of fluid can be injected into a well, storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) efficiency and lifetime of the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids; potential leakage(in CO2Carbon dioxide storage) The escape of injected fluid from the storage formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it to the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) or water column and how to avoid or mitigate it; and the long-term behaviour and fate of the stored CO2Carbon dioxide and displaced brine.
• Chapter 3 - Flow modelling - This chapter describes the modelling of flow and transport mechanisms and the numerical models that are used. The purposes of fluid flow simulations are also illustrated on some examples of CO2Carbon dioxide injectionThe process of using pressure to force fluids down wells pilots.
• Chapter 4 - Reactive flow modelling - This chapter presents an overview of reactive flow modelling (solute transport modelling). The state of current knowledge within geochemical and solute transport modelling is presented as wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injectionThe process of using pressure to force fluids down wells of fluids as an overview of what has to be modelled and for how long. The state of the art of chemical and solute transport modelling and its applications status, concentrating on reactive flow modelling, as wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injectionThe process of using pressure to force fluids down wells of fluids as the important role played by available data are discussed.
• Chapter 5 - Coupled geomechanical and flow modelling - This chapter presents the scope of geomechanical modelling and the data required to assess the long-term performance of CO2Carbon dioxide storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%). The different issues of geomechanical modelling are then presented and illustrated on case studies. Finally, coupling methods are presented.
• Chapter 6 - Environmental impact and riskConcept that denotes the product of the probability of a hazard and the subsequent consequence of the associated event - This chapter presents an overview of the riskConcept that denotes the product of the probability of a hazard and the subsequent consequence of the associated event process that determines both the consequences and likelihood of an event and that is the input for good monitoringMeasurement and surveillance activities necessary for ensuring safe and reliable operation of a CGS project (storage integrity), and for estimating emission reductions and mitigationThe process of reducing the impact of any failure plan.
• Chapter 7 - Economic analysis - This chapter presents the cost associated to CO2Carbon dioxide storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) emphasising the great uncertainties on these costs and their site dependency.
• Chapter 8 - Public perception and acceptance - This is widely perceived to be a potential major impediment to deployment of CCSCarbon dioxide CaptureThe separation of carbon dioxide from other gases before it is emitted to the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) and Storage. Concerns over safety, permanence of storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) and adverse impacts on environment, health and property prices need to be carefully managed at local and national scales. How, when and by whom the CCSCarbon dioxide CaptureThe separation of carbon dioxide from other gases before it is emitted to the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) and Storage message should be delivered are likely to vary from site to site depending on local cultural factors. Therefore, this report does not seek to be prescriptive, but rather, presents references to major studies on the issue.