To demonstrate the safety of CO2Carbon dioxide a huge variety of different information can be used, but the main condition being conformity of the monitored data with the predicted models. The EUEuropean Union Guidance Document states that conformity with the model for at least 5 years before transfer of the liability is required. It is also mentioned that the predictions for wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injection of fluids pressure, location of the CO2 plumeDispersing volume of CO2-rich phase contained in target formation, chemical composition, geochemical changes and surface deformations should lay within a specified uncertainty range, which is defined by the relevant authority.
However, there are different definitions on leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column. The EU CCS DirectiveDirective 2009/31/EC of the European Parliament and of the Council of 23 April 2009 on the geological storage of carbon dioxide 2009/31/ECEuropean Commission states that leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column is the "release of CO2Carbon dioxide from the storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere complex including secondary containmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) formations". The WRI guidelines define leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column as any significant movement of CO2Carbon dioxide outside the confining zone. In the OPA Bill already CO2Carbon dioxide migrating outside the defined migrationThe movement of fluids in reservoir rocks path is considered leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column. In general the definition of the IEAInternational Energy Agency CCSCarbon dioxide Capture and Storage model regulatory framework can be used, where leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column is defined as the unintended release of CO2Carbon dioxide from the storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere complex into the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%).
Methods to demonstrate the safety of stored CO2Carbon dioxide can be any wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injection of fluids monitoringMeasurement and surveillance activities necessary for ensuring safe and reliable operation of a CGS project (storage integrity), and for estimating emission reductions of pressure and geochemistry data in the permeable layer above the confining zone, geophysical imaging of the plume and any surface detection-installations like soil-gas monitoringMeasurement and surveillance activities necessary for ensuring safe and reliable operation of a CGS project (storage integrity), and for estimating emission reductions.
The major factor of post closure is still that the system should show stable conditions or at least be evolving towards long-term stability. For these requirements there are different indicators:
- The rate of change of the key parameters is small or declining; simulations for some thousand years and the requirements for the rate of change of the key parameters is within x%;
- CO2Carbon dioxide is permanently contained. The pressure is lower than the fracturing pressure, geochemistry monitoringMeasurement and surveillance activities necessary for ensuring safe and reliable operation of a CGS project (storage integrity), and for estimating emission reductions and modelling indicate no danger and there is no wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injection of fluids corrosion;
- There is no indication of fault(geology) A surface at which strata are no longer continuous, but are found displaced-fractureAny break in rock along which no significant movement has occurred opening due to micro-seismic events or injectionThe process of using pressure to force fluids down wells pressure;
- InjectionThe process of using pressure to force fluids down wells without any problems.
The requirement of complete stability of the CO2 plumeDispersing volume of CO2-rich phase contained in target formation may be over restrictive as the plume can move horizontally at a slow rate without posing any danger. Also the plume may migrate vertically through a non-conventional sealAn impermeable rock that forms a barrier above and around a reservoir such that fluids are held in the reservoir interval over a large time-scale and the CO2Carbon dioxide may be dissolved or be lost as residual gas. Another possibility may be that the plume is trapped by buoyancyTendency of a fluid or solid to rise through a fluid of higher density and slowly dissolving or mineralizing.
International regulations
The OSPARConvention for the Protection of the Marine Environment of the North-East Atlantic, which was adopted at Paris on 22 September 1992 and London ConventionInternational 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 regulations require a post-cessation, site-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 plan. They state that monitoringMeasurement and surveillance activities necessary for ensuring safe and reliable operation of a CGS project (storage integrity), and for estimating emission reductions should be continued until "confirmation that probability of any future adverse environmental effects has been reduced to an insignificant level". They leave the final decision up to the relevant authority.
The IEAInternational Energy Agency model framework requires that there is no significant riskConcept that denotes the product of the probability of a hazard and the subsequent consequence of the associated event of future leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column or any other irregularity. All the required data should be summarized within a report on CO2Carbon dioxide behaviour in the reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids, the modelling results and the anticipated state of the storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere system. However, no minimum time period is specified.
European regulations
Article 18 of EU CCS DirectiveDirective 2009/31/EC of the European Parliament and of the Council of 23 April 2009 on the geological storage of carbon dioxide 2009/13/ECEuropean Commission requires the operator to show that CO2Carbon dioxide is completely contained and that no leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column is occurring. Further the modelled behaviour should match the predictions and the storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere system should be evolving towards long-term stability.
USA regulations
EPA UIC requires that the operator is obligated to monitor the site to show the location of the plume, the pressure front and to demonstrate that drinking water is not endangered. It is also required to demonstrate that the pressure front and the CO2plume have stabilized for at least 50 years after cessation of injectionThe process of using pressure to force fluids down wells that no additional monitoringMeasurement and surveillance activities necessary for ensuring safe and reliable operation of a CGS project (storage integrity), and for estimating emission reductions is required. This is different to the EUEuropean Union Directive on CO2Carbon dioxide storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere where a trend to stable conditions is required. Also the EPA UIC only mentions drinking water and no other environmental impact caused by the site.
The WRI guidance regulations require data on:
- Location, magnitude and extent of plume and the region of elevated pressure;
- CO2Carbon dioxide movement and pressure matches predictions;
- No evidence of significant leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column or failure of confining zone;
- No potential leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column pathway;
- Proven wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injection of fluids integrity,