Remediation measures are applied in case a significant irregularity in the behaviour of a storage site or a leakage of CO2 from a storage site occurs. They can be divided into three categories, depending on the nature of the event. The first category applies to wells and includes well intervention techniques that can mostly be based on proven practice from the oil and gas industry. The second group refers to leakage through geological pathways like caprock failures or faults. In this case the remediation measures usually involve injection and pressure management modifications and/or use of low-permeability "healing" materials. The third case is leakage into overlying aquifers (including potable groundwater resources and near-surface structures) where techniques common in hydrogeology and pollution control are considered.

A special group of newly developed techniques, directed specially at remediation of CO2 storage sites, include application of special materials (special cements, self-healing substances, etc.) or specifically tailored aquifer management techniques. These techniques are the subject of intensive on-going research and development, and further improvements in this field are expected in the near future.

Remediation measures are an integral part of regulatory regimes for CCS in all relevant countries and regions where CCS activities are on-going or planned. The CO2QUALSTORE guideline (Aarnes et al., 2010) considers contingency and remediation planning an essential part of the risk and uncertainty management, providing a systematic approach to the issue. The European regulatory framework is based on the EU CCS Directive (2009) and Guidance Documents 1 and 2 (2011). The key instrument is the risk-based and site-specific corrective measures plan which has to be prepared by the storage site operator as part of storage permit application.

The international comparison shows that most of the regimes are based on similar foundations, closely linking risk assessment, monitoring and remediation measures into one mutually interconnected package. The European and U.S. legislations appear to be the most detailed and most elaborated.

The main aim of geological storage of carbon dioxide is to safely and permanently store the captured CO2 and prevent it from migrating out of the storage formation and entering the atmosphere. It is expected that well selected, sufficiently investigated and carefully operated and monitored storage sites will meet this target thanks to the various trapping mechanisms existing in the storage formation.

It is, however, important to consider the probability that CO2 may escape out of the storage formation, migrate within the storage complex or even leak out of it into the shallower sub-surface or up to the atmosphere. Although such an event would cast in doubt the CCS technology and may also adversely affect the public acceptance of the technology; if it can be demonstrated that any such event can be remediated in a simple and cost-effective way, this would be very important for policy makers, regulators, site operators and the general public (Kuuskraa and Godec, 2007). It is, therefore, very important to have sufficient knowledge about what can be done if leakage from the storage formation is detected. This chapter provides a brief summary of available remediation techniques and an overview of regulatory regimes related to remediation of leaking storage sites both in Europe and worldwide.


in depth

5.1 Site remediation measures

Remediation measures (often also called corrective measures) are applied in case a significant irregularity in the behav...

5.2 Regulatory regimes and guidelines relevant to CO2 storage remediation

A systematic approach to the selection and qualification of storage sites and projects for CO2 geological storage is pro...