This chapter provides an overview on the methods and the regulatory requirements for CO2 injection sites over the period of closure and post closure. It is structured chronologically, starting with the process of abandoning the injection wells and concludes with an overview of how the liability for the project site can be transferred to the relevant authorities.

The first part briefly discusses the different regulations concerning CO2 site closure, which are still under development (especially the national directives). The chapter also provides information on already existing requirements for well abandonment in the hydrocarbon industry, using international conventions as well as accessible regulatory data from countries engaged in oil and gas production. The regulations for decommissioning of oil and gas production operations have already served as a general basis for developing guidelines concerning the handling of CO2 sites because of the similarity of the subject.

Among the activities conducted during site abandonment, well abandonment is considered the most important process, as it should prevent all physical hazard induced by the well, prevent any migration of contaminants and ensure that no communication between originally separated hydrological systems is occurring. Therefore, the chapter also provides a brief overview on the potentially required technical details (plug placement) as well as overall objectives of proper well abandonment (preserve hydrogeological systems).

Following well abandonment, the post-closure phase is described, starting with a brief discussion on how to prove the safety of stored CO2. After summarising the iterative process of characterisation of the reservoir, the general requirements for long-term storage safety, certain modelling techniques, risk management and suitable monitoring options are discussed. As all monitoring plans must be chosen according to the particular risks of the project, a variety of monitoring options also are presented.

The last step in the post-closure phase is represented by the transfer of liability. Exemplary regulations, like the EU Guidance Documents are discussed briefly.

Generally the phase of closure and post-closure is the part of the CCS life-cycle that has been practised the least, which leaves room for developments and discussion, especially concerning the final step of transferring the responsibility of the site.

The following sections provide an overview on the methods and the regulatory requirements for CO2 injection sites over the period of closure and post closure. Primarily based on the "Report on the international regulatory requirements on CO2 geological storage and site abandonment" (Korre, 2011) and the "D1.2 Report on the current site abandonment methodologies in relevant industries" (Wollenweber, 2012) by the project CO2Care - CO2 Site Closure Assessment Research the objective is to summarise and provide updates on international, EU and national directives as well as guidelines for abandonment methodologies.

Site abandonment is generally defined as any actions taken by the operator to close down a previously operating field. The regulations concerning CO2 site closure are, especially the national directives, still in a stage of development. That is why additionally the chapter gives information on the already existing requirements for well abandonment in the hydrocarbon industry, which due to the similarity of the subject already served as basis for guidelines concerning the handling of CO2 sites. Also many CCS projects will need to know the conditions of existing/abandoned oil and gas wells to decide if they are suitable for use in CO2 storage.

Concerning CO2 site closure there are a few terms which are frequently used but have slightly varying meanings for the different regulations in use.

Generally in the UK and the EU, the term "closure" defines the moment of cessation of CO2 injection. Internationally the US UIC (Underground Injection Control) and IEA (International Energy Agency) speak of closure when the operator is released from site care. IEA mentions additionally a "closure period" which defines the time between cessation of injection and the point when the operator is no longer responsible for the site. Abandonment defines the general process required when the well is no longer in use. "Post closure" is the period after the end of injection. Different protocols provided by IEA (International Energy Agency), IOGCC (Interstate Oil and Gas Compact Commission) and WRI (World Resources Institute) define "post closure" as the period after a certification of closure (by the appropriate authority). This certification may also contain the release of the operator and the "transfer of liability", which defines the moment when site care is transferred to the authorities or when the authority certifies that the site is safe.


in depth

6.1 Well abandonment, site closure procedures and regulations

Among the activities included in proper site abandonment, well abandonment is considered the most important process....

6.2 Proving the safety of CO2 site post closure

There are several abandonment steps covering this time-interval of the CCS methodology, which starts with the cessation ...

6.3 Transfer of liability

Regulations typically consider the liability transfer of the site after safety of the wells and the CO2 plume is demonst...

6.4 Conclusions

There are sometimes large variations in the requirements concerning modelling, risk assessment, monitoring and safety de...