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[[file:SiteCharacterization.JPG|thumb|400px|{{figure number|3}}Site characterization methodology for the geological storage of CO₂.<ref name=Gibsonpoole_2009>Gibson-Poole, C. M., 2009, Site characterization for geological storage of carbon dioxide: Examples of potential sites from northwest Australia: Unpublished Ph.D. thesis, University of Adelaide, Adelaide, Australia, 258 p.</ref>]]

[[file:SiteCharacterization.JPG|thumb|400px|{{figure number|3}}Site characterization methodology for the geological storage of CO₂.<ref name=Gibsonpoole_2009>Gibson-Poole, C. M., 2009, Site characterization for geological storage of carbon dioxide: Examples of potential sites from northwest Australia: Unpublished Ph.D. thesis, University of Adelaide, Adelaide, Australia, 258 p.</ref>]]

Different levels of site characterization can be undertaken depending on the maturity of the project ([[:file:SiteCharacterization.JPG|Figure 3]]). Initially, a regional characterization process is needed to establish the potential of an area for CO₂ geological storage before an actually site location is selected. Sedimentary basins across a state or country can be screened and ranked as to their overall suitability for CO₂ storage, using criteria suggested by Bachu,<ref name=Bachu_2003>Bachu, S., 2003, Screening and ranking of sedimentary basins for sequestration of CO₂ in geological media in response to climate change: Environmental Geology, v. 44, no. 3, p. 277–289.</ref> such as [[tectonic setting]], [[basin]] size and depth, intensity of faulting, [[hydrodynamic]] and [[geothermal]] regimes, existing resources, and industry maturity. Once a basin has been identified as suitable, a regional assessment can be undertaken to locate possible storage sites<ref name=Bradshawandrigg_2001 /><ref name=Riggetal_2001 /><ref name=Bradshawetal_2002 /> ([[:file:SiteCharacterization.JPG|Figure 3]]). The stratigraphy is reviewed to identify suitable rock combinations that may provide [[reservoir]] and [[Seal rock|seal]] pairs, and data gathered to assess five key factors: storage capacity (will it meet the volume requirements of currently identified CO₂ sources, e.g., pore volume, area, and temperature or pressure?); injectivity potential (are the reservoir conditions viable for injection, e.g., [[permeability]], [[porosity]], and thickness?); site details (is the site economically and technically viable, e.g., onshore or offshore, distance from source, and depth to top reservoir?); containment (will the seal and trap work for CO₂, e.g., [[seal capacity]] and [[Seal thickness|thickness]], trap type, and faults?); and existing natural resources (are there viable natural resources at the site that may be compromised, e.g., proven petroleum system, groundwater, coal, or other natural resource?).<ref name=Bradshawandrigg_2001 /><ref name=Riggetal_2001 /><ref name=Bradshawetal_2002 /> These five factors provide a useful ranking scheme for describing the key elements of any potential CO₂ geological storage site and can be used to compare and contrast the relative merits of one potential site over another site.

Different levels of site characterization can be undertaken depending on the maturity of the project ([[:file:SiteCharacterization.JPG|Figure 3]]). Initially, a regional characterization process is needed to establish the potential of an area for CO₂ geological storage before an actually site location is selected. Sedimentary basins across a state or country can be screened and ranked as to their overall suitability for CO₂ storage, using criteria suggested by Bachu,<ref name=Bachu_2003>Bachu, S., 2003, Screening and ranking of sedimentary basins for sequestration of CO₂ in geological media in response to climate change: Environmental Geology, v. 44, no. 3, p. 277–289.</ref> such as [[tectonic setting]], [[basin]] size and depth, intensity of faulting, [[hydrodynamic]] and [[geothermal]] regimes, existing resources, and industry maturity. Once a basin has been identified as suitable, a regional assessment can be undertaken to locate possible storage sites<ref name=Bradshawandrigg_2001 /><ref name=Riggetal_2001 /><ref name=Bradshawetal_2002 /> ([[:file:SiteCharacterization.JPG|Figure 3]]). The stratigraphy is reviewed to identify suitable rock combinations that may provide [[reservoir]] and [[seal]] pairs, and data gathered to assess five key factors: storage capacity (will it meet the volume requirements of currently identified CO₂ sources, e.g., pore volume, area, and temperature or pressure?); injectivity potential (are the reservoir conditions viable for injection, e.g., [[permeability]], [[porosity]], and thickness?); site details (is the site economically and technically viable, e.g., onshore or offshore, distance from source, and depth to top reservoir?); containment (will the seal and trap work for CO₂, e.g., [[seal capacity]] and [[Seal thickness|thickness]], trap type, and faults?); and existing natural resources (are there viable natural resources at the site that may be compromised, e.g., proven petroleum system, groundwater, coal, or other natural resource?).<ref name=Bradshawandrigg_2001 /><ref name=Riggetal_2001 /><ref name=Bradshawetal_2002 /> These five factors provide a useful ranking scheme for describing the key elements of any potential CO₂ geological storage site and can be used to compare and contrast the relative merits of one potential site over another site.

Once a preferred site has been selected, it can proceed to a detailed site evaluation,<ref name=Gibsonpooleetal_2005 /><ref name=Gibsonpoole_2009 /> the first step of which is the establishment of a structural and stratigraphic framework ([[:file:SiteCharacterization.JPG|Figure 3]]). A [[Sequence stratigraphy|sequence-stratigraphic]] approach is adopted because it focuses on key surfaces that allow [[lithofacies]] distributions to be predicted. This is vital in understanding the likely distribution and connectivity of reservoirs and seals. Of the five key factors discussed above, the ones that require detailed geological assessment are injectivity, containment, and capacity. Injectivity issues include the geometry and connectivity of individual [[Flow units for reservoir characterization|flow units]], the nature of the [[Geological heterogeneities|heterogeneity]] within those units (i.e., the likely distribution and impact of baffles), and the physical quality of the reservoir in terms of porosity and permeability characteristics. Containment issues include the distribution and continuity of the seal, the seal capacity (maximum CO₂ column height retention), CO₂-water-rock interactions (potential for mineral trapping), potential [[migration]] pathways (structural trends, distribution and extent of intraformational seals, and formation water flow direction and rate), and the integrity of the reservoir and seal (fault and fracture stability and maximum sustainable pore fluid pressures). Potential CO₂ storage capacity can be assessed geologically in terms of available pore volume; however, the efficiency of that storage capacity will be dependent on the rate of CO2 migration, the [[dip]] of the reservoir, the heterogeneity of the reservoir and the potential for [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=spill%20point fill-to-spill] structural closures encountered along the migration path, and the long-term prospects of residual gas trapping, dissolution into the formation water, or precipitation into new minerals. The geologically calculated pore volume provides the basis for numerical [[flow simulation]]s of CO₂ injection and storage, which will give a more accurate assessment of how much of the available pore volume is actually used (sweep efficiency).

Once a preferred site has been selected, it can proceed to a detailed site evaluation,<ref name=Gibsonpooleetal_2005 /><ref name=Gibsonpoole_2009 /> the first step of which is the establishment of a structural and stratigraphic framework ([[:file:SiteCharacterization.JPG|Figure 3]]). A [[Sequence stratigraphy|sequence-stratigraphic]] approach is adopted because it focuses on key surfaces that allow [[lithofacies]] distributions to be predicted. This is vital in understanding the likely distribution and connectivity of reservoirs and seals. Of the five key factors discussed above, the ones that require detailed geological assessment are injectivity, containment, and capacity. Injectivity issues include the geometry and connectivity of individual [[Flow units for reservoir characterization|flow units]], the nature of the [[Geological heterogeneities|heterogeneity]] within those units (i.e., the likely distribution and impact of baffles), and the physical quality of the reservoir in terms of porosity and permeability characteristics. Containment issues include the distribution and continuity of the seal, the seal capacity (maximum CO₂ column height retention), CO₂-water-rock interactions (potential for mineral trapping), potential [[migration]] pathways (structural trends, distribution and extent of intraformational seals, and formation water flow direction and rate), and the integrity of the reservoir and seal (fault and fracture stability and maximum sustainable pore fluid pressures). Potential CO₂ storage capacity can be assessed geologically in terms of available pore volume; however, the efficiency of that storage capacity will be dependent on the rate of CO2 migration, the [[dip]] of the reservoir, the heterogeneity of the reservoir and the potential for [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=spill%20point fill-to-spill] structural closures encountered along the migration path, and the long-term prospects of residual gas trapping, dissolution into the formation water, or precipitation into new minerals. The geologically calculated pore volume provides the basis for numerical [[flow simulation]]s of CO₂ injection and storage, which will give a more accurate assessment of how much of the available pore volume is actually used (sweep efficiency).