In case a leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column occurs as a result of an unexpected flaw in the geological system, this is most likely to result from caprockRock of very low permeability that acts as an upper seal to prevent fluid flow out of a reservoir failure, faults and fracturing, overfilling the storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids beyond spill pointThe structurally lowest point in a structural trap that can retain fluids lighter than background fluids or up-dip(geology) The steepest angle of descent of a tilted rock strata or feature relative to a horizontal plane leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column. Due to the limited access to the geological structures at depth, the possibilities to correct or repair the containmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) capacity of the system are usually restricted to a general set of measures associated with wells and injectionThe process of using pressure to force fluids down wells operations management (Guidance Document 2, ECEuropean Commission, 2011b). Remediation measures can be deployed either to reduce or prevent further leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column or to try to correct and remediate the leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column itself, and any impacts at surface.
There are several viable techniques based on stopping the pressure increase in all or part of the reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids, or reducing the pressure. The main techniques are (Guidance Document 2, ECEuropean Commission, 2011b):
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Limiting CO2Carbon dioxide injectionThe process of using pressure to force fluids down wells rates and pressure build-up in specific wells or across the site, either temporarily or permanently. This would reduce pressure build-up in all or part of the reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids and may be used to address caprockRock of very low permeability that acts as an upper seal to prevent fluid flow out of a reservoir related issues and fracturing. This type of measure is straightforward to apply.
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Reducing the reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids pressure by extracting CO2Carbon dioxide or water from the storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids or complex. By decreasing the pressure gradient this may help cease or reverse the impacts of faulting, fractures, spill and any migrationThe movement of fluids in reservoir rocks out of the storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere complex. This can be done in a number of ways:
- ReductionThe gain of one or more electrons by an atom, molecule, or ion of CO2Carbon dioxide injectionThe process of using pressure to force fluids down wells pressure (e.g. by using lower injectionThe process of using pressure to force fluids down wells rate, or more injectionThe process of using pressure to force fluids down wells wells);
- Stopping CO2Carbon dioxide injectionThe process of using pressure to force fluids down wells;
- Producing back injected CO2Carbon dioxide from the storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids/plume (actively reducing reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids pressure) and either controlled venting or re-injectionThe process of using pressure to force fluids down wells in another site;
- Peripheral extraction of formation waterWater that occurs naturally within the pores of rock formations or other fluids;
- Increase of reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids capacity and steering CO2Carbon dioxide in favourable directions by hydrofracturing (this would create pathways to develop and access new compartments of the storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids away from leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column areas; by expanding the storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere container, the pressure will decrease).
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Extraction of CO2Carbon dioxide at or near an identified leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column point, zone or pathway (in contrast to extraction from storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids). This will depend on pinpointing leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column zones and is likely to require new targeted extraction wells. In some cases it may be possible to intersect leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column zones with existing wells by:
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Sealing regions where leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column is occurring such as identified fault(geology) A surface at which strata are no longer continuous, but are found displaced or caprockRock of very low permeability that acts as an upper seal to prevent fluid flow out of a reservoir leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column pathways in limited areas by injecting low-permeabilityAbility to flow or transmit fluids through a porous solid such as rock materials (e.g. foam or grout).
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Increase of pressure in formations upstream of CO2Carbon dioxide leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column, creating a hydraulic barrier (decreasing pressure gradient).
One should be aware of the status and limitations of different techniques and methods. While several of these measures involve commonly employed practices in oil and gas industry or environmental remediation, some comprise innovative concepts or include expensive operations such as drilling of new wells. The natural geological system contains many heterogeneities and discontinuities. As a result, leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column is not easily undone, so that choices to repair are limited and rather tend to be directed at mitigationThe process of reducing the impact of any failure. Furthermore, the effectiveness of all the measures is strongly determined by the site-specific geological system, the nature of the actual leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column or irregularity and the status of the specific method or technique (Guidance Document 2, ECEuropean Commission, 2011b).