5.1 Site remediation measures

Remediation measures (often also called corrective measures) are applied in case a significant irregularityAny 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 in the behaviour of a storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere site or a leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column of CO2Carbon dioxide from a storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere site occurs. The method and type of remediation required will be dictated by the nature of the significant irregularityAny 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 or leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column. The main generic leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column pathways and irregular behaviour types can be summarised as follows (Guidance Documents 1and 2, ECEuropean Commission, 2011a, b):

• Geological

  • CO2Carbon dioxide leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column due to caprockRock of very low permeability that acts as an upper seal to prevent fluid flow out of a reservoir failure - caprocks may be ineffective in containing CO2Carbon dioxide, unexpectedly absent over part of the storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere area, or degraded as a result of geochemical reactions and/or hydrocarbon depletion;
  • CO2Carbon dioxide leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column via faults and fractures - leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column through natural geological pathways, or resulting from CO2Carbon dioxide injectionThe process of using pressure to force fluids down wells and build up in the reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids, hydrocarbon depletion, natural or induced seismic activity;
  • Overfilling beyond spill pointThe structurally lowest point in a structural trap that can retain fluids lighter than background fluids - structural spill out of the trap(geology) A geological structure that physically retains fluids that are lighter than the background fluids, e.g. a convex fold, where the reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids is smaller than expected and/or over-filled;
  • UpdipInclining upwards following a structural contour of strata leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column - leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column through high permeabilityAbility to flow or transmit fluids through a porous solid such as rock intervals, of particular relevance to stratigraphicThe order and relative position of geological strata 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 or migrationThe movement of fluids in reservoir rocks assisted storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere.

• Manmade

  • CO2Carbon dioxide leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column through wells and boreholes - caused by wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injection of fluids integrity issues;
  • Pathways associated with mining activity.

• Other

  • Risks relating to groundwater including effects that arise directly from the effect of dissolved CO2Carbon dioxide in the formation waterWater that occurs naturally within the pores of rock formations, including heavy metal mobilisation;
  • Indirect effects from groundwater contamination by displaced brine;
  • Oil or gas leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column or emissions that could result from the displacement of hydrocarbons in underground formations by CO2Carbon dioxide injectionThe process of using pressure to force fluids down wells and movement;
  • Any risks relating to movement of other hazardous components such as H₂S;
  • Ground movement, uplift and/or subsidence;
  • Natural seismicityThe episodic occurrence of natural or man-induced earthquakes, seismic hazards and tectonics, including exposure earthquakes;
  • Effects from sabotage or terrorism.

A significant distinction needs to be made between remediation measures that can be applied to the two major types of leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column pathways - geological and manmade. While corrective measures and repairs to wells (most frequent manmade pathways) are often technically feasible, the effectiveness of corrective measures and potential of restoring the geological system in general is limited. However, corrective measures that involve early interventions and modifications to injectionThe process of using pressure to force fluids down wells operations will usually be beneficial (Guidance Document 2, ECEuropean Commission, 2011b).

In principle, wells can be accessed, allowing tools to be run or operations to be performed in order to repair leakages or significant irregularities of the wellboreThe 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 and its immediate surroundings. Unlike wells where the location of any anomaly is usually known and pinpointed, geological anomalies are more likely to be three-dimensional problems, of significant vertical and/or lateral extent, and where the precise location of any failure points is uncertain. In addition flaws in the geological system can typically be corrected only when wells are penetrating the affected zone. This seriously reduces the options to repair the geological anomalies, making early detection through monitoringMeasurement and surveillance activities necessary for ensuring safe and reliable operation of a CGS project (storage integrity), and for estimating emission reductions and early intervention important. Hence, it is important to carefully integrate the monitoringMeasurement and surveillance activities necessary for ensuring safe and reliable operation of a CGS project (storage integrity), and for estimating emission reductions plans and activities with the corrective measures. MonitoringMeasurement and surveillance activities necessary for ensuring safe and reliable operation of a CGS project (storage integrity), and for estimating emission reductions should be used to detect anomalies and trigger early mitigationThe process of reducing the impact of any failure measures.