Guidance document 1CO2 storage life cycle and risk management framework

EUROPEAN COMMISSION
Directorate-General for Climate Action
This document has been prepared with the assistance of DNV Netherlands B.V. under contract to theEuropean Commission (Service contract No 090203/2022/881796/SER/CLIMA.C.2)
It has also greatly benefited from discussions with, and information supplied by, experts from Member
States within the framework of the Expert Group on the geological storage of carbon dioxide and with key
stakeholders during a targeted stakeholder consultation. DG CLIMA gratefully acknowledges contributions
from other Commission departments (COMP, ENER, ENV, MARE, GROW, REGIO, SANTE, RTD, JRC,
SG, and SJ) to the work to finalise the guidance documents.
E-mail: CLIMA-CCS-DIRECTIVE@ec.europa.eu

European Commission
B-1049 Brussels

EUROPEAN COMMISSION

Guidance document 1CO2 storage life cycle and risk management framework

Directorate-General for Climate Action
2024

The aim of this guidance document is to contribute to a better understanding of the requirements of Directive
2009/31/EC on the geological storage of carbon dioxide. It has been prepared by the European Commission
on the basis of the views and knowledge provided by stakeholders. The purpose of this guidance is
explanatory and illustrative. It does not create any rights or obligations.

Manuscript completed in July 2024

This document has been prepared for the European Commission however it reflects the views only of theauthors, and the European Commission is not liable for any consequence stemming from the reuse of thispublication.
© European Union, 2024

The reuse policy of European Commission documents is implemented by Commission Decision
2011/833/EU of 12 December 2011 on the reuse of Commission documents (OJ L 330, 14.12.2011,
p. 39). Unless otherwise noted, the reuse of this document is authorised under a Creative Commons
Attribution 4.0 International (CC BY 4.0) licence (https://creativecommons.org/licenses/by/4.0). This meansthat reuse is allowed provided appropriate credit is given and any changes are indicated.

Guidance document 1

Contents

1.

Revision history ....................................................................................... 62.

Introduction .............................................................................................. 7
2.1. Purpose and scope of guidance documents .......................................... 7
2.2. Legislative context ................................................................................. 7
2.3. Acronyms ............................................................................................... 92.4. Interpretation of main terms ................................................................. 12

3.

Main phases and regulatory steps ....................................................... 19
3.1. Main phases ........................................................................................ 19
3.2. Interaction between operators and competent authorities ................... 23

4.

Risk management approach ................................................................. 24
4.1. Key principles ...................................................................................... 24
4.2. Risk evaluation criteria ......................................................................... 25
4.2.1. Categories of likelihood........................................................................... 26
4.2.2. Categories of consequence – human health ........................................... 26
4.2.3. Categories of consequence – environment ............................................. 26
4.2.4. Assessing the level of insignificant risk ................................................... 27
4.2.5. Example: how to compare the aggregate risk profile with the expected
benefits of the project.............................................................................. 27

4.3. Risk assessment.................................................................................. 28
4.3.1. General guidance ................................................................................... 28
4.3.2. Hazard characterisation .......................................................................... 30
4.3.3. Exposure and effects assessment .......................................................... 34
4.3.4. Risk characterisation............................................................................... 35

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Guidance document 1

1. Revision history
Key changes since the previous version•

The document was significantly shortened and re-structured with the emphasis on providing
guidance on how to implement the requirements in the CCS Directive.

•

Tables were added to illustrate understanding of key defined and non-defined terms.

•

Clarifications were provided related to project phases and the associated requirements.

•

Additional guidance on recital 20 was provided.

•

A new subsection on risk evaluation criteria was introduced. Among others, it was clarified that risk
assessments must evaluate three distinct consequences: leakage, damage to the environment anddamage to human health.

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Guidance document 1

2. Introduction
2.1.

Purpose and scope of guidance documents

This guidance document (GD) forms part of a set of guidance documents as follows:●

Guidance document 1: CO2 storage life cycle and risk management framework;●

Guidance document 2: Characterisation of the storage complex, CO2 stream
composition, monitoring and corrective measures;●

Guidance document 3: Criteria for transferring responsibility to the competentauthority;●

Guidance document 4: Financial security and financial contribution.

The aim of these GDs is to improve understanding of the requirements of Directive
2009/31/EC on the geological storage of carbon dioxide (the ‘CCS Directive’) and giveindications on how it can be implemented. They should therefore facilitate a correct anduniform application of the CCS Directive across the EU. The guidance does not represent
an official position of the Commission and is not legally binding. The binding
interpretation of EU legislation is the exclusive competence of the European Court ofJustice that can make final judgments concerning the interpretation of the CCS Directive.
GD 1 is structured as follows. The remainder of this Section 2 describes the legislative
context for CO2 storage risk management under the CCS Directive and provides aninterpretation of some of the key terms used in the CCS Directive. Section 3 provides
guidance to competent authorities on the main phases of a CO2 storage project, theassociated key activities for authorities and operators, and the main points of interaction
between the authorities and operators. Section 4 describes the overall approach to risk
management for CO2 storage sites, and how to demonstrate that there is no significant
risk of leakage, and no significant environmental or health risks.

2.2.

Legislative context

The CCS Directive establishes a legal framework for the geological storage of CO2. It
specifies that environmentally safe CO2 geological storage means the permanentcontainment of CO2 in such a way as to prevent and, where this is not possible, eliminate
as far as possible negative effects and any risk to the environment and human health(CCS Directive, Article 1). This document provides guidance to operators and competentauthorities on how to interpret and implement the obligations for risk management related
to the following requirements in the CCS Directive:●

Article 4(4): A geological formation shall only be selected as a storage site, if
under the proposed conditions of use there is no significant risk of leakage, and
if no significant environmental or health risks exist.

●

Annex I, Step 3.3: Risk assessment:o3.3.1: Hazard characterisation – site-specific risk identification.
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Guidance document 1

o

3.3.2: Exposure assessment – based on the hazards identified.

o

3.3.3: Effects assessment – based on the hazards identified.

o

3.3.4: Risk characterisation – based on the hazard, exposure and effects
assessment.

Apart from the ban on storing CO2 storage in the water column1 and the requirements
set out in the Water Framework Directive 2000/60/EC2, the CCS Directive is notprescriptive regarding the type of storage option or formation that can be used forgeological storage. The CCS Directive allows for storage in sedimentary and igneous
aquifers, hydrocarbon fields, coal seams, and in principle other options such as salt
caverns. However, the CCS Directive is prescriptive on the required characteristics of asuitable storage complex. It states that all prospective storage sites must meet therequirement in Article 4(4): under the proposed conditions of use there is no significant
risk of leakage, and no significant environmental or health risks. However, from a risk
perspective, knowledge from previous operations at the storage site can be leveraged todemonstrate conformance with this requirement.
There may also be circumstances where CO2 is injected into the subsurface as part ofenhanced hydrocarbon recovery (EHR) operations, or as part of geothermal operations(e.g. re-injection of produced CO2, or using CO2 as a geothermal working fluid). If the
primary aim of such operations is the permanent and environmentally safe storage ofCO2, a risk-based approach suited for CO2 storage projects should be used. This is also
reflected in Recital 20 in the CCS Directive which states that ‘the provisions of the CCS
Directive should apply if EHR is combined with geological storage of CO2’ (see Box 1).
In Europe, EHR is typically permitted under the regulations governing petroleum
exploration and production, which may not require compliance with all requirements of
the CCS Directive. Similarly, geothermal operations are generally permitted underregulations specific to geothermal energy projects with no requirement to ensure thecontainment of any re-injected CO2 or CO2 used as working fluid. If the operators of ageothermal installation capture and reinject CO2 underground in order to reduce GHG
emissions, they will need to apply for CO2 storage permit in accordance with Directive
2009/31/EC in addition to any other permit needed for their operation. This, however,does not apply in the cases where the CO2 reinjection is configured in a closed cycle
system, being contained within the system for the entire operation, including geothermal
systems that reinject exclusively CO2 originating from the same aquifer.

1 According to the definition of water column, Article 3(2) of the CCS Directive.
2 Amended by Article 32 of the CCS Directive.

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Guidance document 1

Box 1: How the CCS Directive applies to enhanced hydrocarbon recovery.
Recital 20 in the CCS Directive states that 'EHR is not in itself included in the scopeof this Directive. However, where EHR is combined with geological storage of CO 2,
the provisions of this Directive for the environmentally safe storage of CO 2 should
apply’. EHR is considered combined with geological storage of CO2 when long-term(permanent) storage of CO2 to contribute to the fight against climate change is a
primary objective along with the objective to enhance hydrocarbon recovery. A
general implication of being a primary objective is that the operator seeks
opportunities to maximise the volume of CO2 stored beyond what is incentivised by
the economic benefit from incremental hydrocarbon production.
With this interpretation in mind, the following two types of EHR operations qualify:
1.

Operations where CO2 is injected in the aquifer support (water leg) partof a hydrocarbon-bearing formation, and the CO2 operation is managed
and monitored for the purpose of long-term storage. There may be somepressure influence that helps maintain reservoir pressure (and limit theneed for water injection), but long-term storage of CO2 and the associatedeconomic and climate benefits is the primary driver for the CO2 injection.

2.

Operations where an EHR operator seeks to maximise the volume of CO2
injected into the hydrocarbon field, and it can be demonstrated that thevolume of CO2 injected exceeds the life-cycle emissions of the EHR
operations, including emissions generated by the combustion ofincremental hydrocarbon production.

2.3.

Acronyms

Table 1: List of the acronyms used in the in GDs 1 through 4.
Acronym

Meaning

2D
3D
4D
A
ALARP

Two-dimensional
Three-dimensional
Four-dimensional
Area of basin or hydraulic unit
As low as reasonably practicable

ARMA
BY
BV
CC
CCS

American Rock Mechanics Association
By attribution
Besloten vennootschap (Dutch: private limited company)
Creative Commons
Carbon capture and storage

CCSA
CEA
CLIMA
CO2
DNV
CO2StoP
COMP
DG

Carbon Capture & Storage Association
European insurance and reinsurance federation
Climate Action
Carbon dioxide
Det Norske Veritas
CO2 Storage Potential in Europe
Competition
Directorate-General

9Guidance document 1

Acronym

Meaning

E
EC
EEA

Storage efficiency factor
European Commission
European Economic Area

EEC
EED
E.g.
EHR

European Economic Community
Energy Exploration and Development
Exempli gratia (Latin: for example)
Enhanced hydrocarbon recovery

ENER
ENV
EPA

EnergyEnvironment
Environmental Protection Agency

Etc.
ETS

Et cetera (Latin: and so forth)
Emission Trading Scheme

EU
EUA
FG
EUR
GCCSI
GD

Euopean Union
Emission Unit Allowance
Fracture gradientEuros (€)
Global Carbon Capture and Storage Institute
Guidance document

GROW
h
H2
H2S
H2O
Hg
I.e.

Internal Market, Industry, Entrepreneurship and Small and Midsize Enterprises
Net thickness of the hydraulic unit
HydrogenHydrogen sulfide
Water
Mercury
Id est (Latin: that is)International Energy Agency Greenhouse Gas Research & Development
Programme
International Panel on Climate ChangeInternational Organization for Standardization
Joing Research Centre
Kilograms
Legislation
Low Carbon Fuel Standard
Legal Services
MetersMaritime Affairs and Fisheries
Mass of CO2
Monitoring and Reporting Regulation
Million tonnes
Monitoring and Reporting Guidelines
Moment magnitude
NitrogenNot applicable
North-East Atlantic Environment Strategy
Nitric oxides
Net to gross
Norsk Sokkels Konkurranseposisjon
Netherlands Oil and Gas Exploitation and Production Association
OxygenOffshore Energies UK
Oil and Gas Climate Initiative
Official Journal
50th percentile (mean)
90th percentile

IEAGHG
IPCC
ISO
JRC
kg
L
LCFS
LS
m
MARE
MCO2
MRR
Mt
MRG
MW
N2
N/A
NEAES
NOX
n/g
NORSOK
NOGEPA
O2
OEUK
OGCI
OJ
P50
P90

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Guidance document 1

Acronym

Meaning

pH
ϕ
P&A
ρCO2
REGIO
RP
RTD
S3
SANTE
SG
SOX
SPE
SRMS
t

Potential for hydrogen ion concentration
Average effective porosity
Plugging and abandonment
Density of CO2
Regional and Urban Policy
Recommended practiceResearch and Innovation
Minimum total principal stress
Health and Food Safety
Secretariat-General
Sulphur oxides
Society of Petroleum Engineers
Storage Resources Management System
TonnesT.b.d.
TFEU
UK
URDG
US
USA
Vb
ZEP

To be determined
Treaty on the Functioning of the European Union
United Kingdom
Uniform Rules for Demand Guarantees
Of the United States of America
United States of America
Bulk volume
Zero Emissions Platform

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Guidance document 1

2.4.

Interpretation of main terms

Table 2: Clarification of the key defined terms used in the CCS Directive.
Term

Storage site

Definition in CCS Directive

A defined volume area withina geological formation used
for the geological storage of
CO2 and associated surface
and injection facilities.

12

Comments
The storage site should be described for eachgeological storage project. The subsurface
component of the storage site must be
contained within the storage complex. Thissubsurface volume should be delineated bylateral boundaries on an area map, andvertically by describing the geological stratum(or strata) into which CO2 stream(s) areinjected. These strata are often referred to as
storage reservoirs. The surface and injection
facilities considered to be part of the storagesite should be identified. The storage site
includes the injection and monitoring wells. It
may also include associated infrastructuresuch as pipelines, CO2 conditioning systems,
storage tanks, offshore platforms and floating(storage and) injection units.
Note: The boundary of the ‘surface andinjection facilities’ is not explicitly defined in
the Directive. It is generally understood thatthese facilities start where the transportsystem ends. For onshore projects, this canbe at custody transfer meters for each CO2
stream receiving line. For offshore projects,
however, custody transfer meters can beonshore, prior to ship loading or injection into
the offshore pipeline. It is therefore proposed
to define the limits of the surface facilities tobe the facilities after any custody transfer
carried out within the ‘surrounding area’ (seedefinition below).

Guidance document 1

Term

Definition in CCS Directive

Comments
A storage permit application must, under
Article 7(3), include a description andcharacterisation of the storage complex.

Storage complex

The storage site andsurrounding geologicaldomain which can have aneffect on overall storage
integrity and security; that is,secondary containment
formations.

The storage complex must be contained
within the license area for the storage site, but
it can have the same lateral boundaries as thelicense area. The storage complex must
include the volume where a CO2 plume may
be present, but will often include areas ofpotential lateral migration outside theexpected extent of any CO2 plumes. However,
elevated pressure may extend beyond thelimits of the storage complex.
Vertically, the storage complex will normallyincorporate shallower geological formations
that provide physical trapping of buoyant
formation fluids, including any CO2 plumes.
The storage complex also contains the
subsurface component of the storage site,which can include several geologicalformation(s)/stratigraphic interval(s) into which
CO2 is injected.
The storage complex must include all legacy
wells within the surrounding area that havethe potential to provide leakage pathways.
This includes all legacy wells that penetrate
the caprock.

Hydraulic unit

CO2 plume

A hydraulically connected
pore space where pressurecommunication can bemeasured by technicalmeans and which isbordered by flow barriers,
such as faults, salt domes,
lithological boundaries, or by
the wedging out or
outcropping of the formation.

The hydraulic unit containing the subsurface
volume for the storage site is important for
determining the expected pressure build-up
from the geological storage project, which isalso a key determinant for storage capacity
and sustained injectivity. The hydraulic unit
should therefore be mapped and described atleast over an area extent where materialchanges in pressure can occur as a result of
the CO2 injection activities. This mapping
should also describe other known activities
within the hydraulic unit that may impact
pressure within the storage site.

The dispersing volume of
CO2 in the geologicalformation.

This refers to CO2 in free-phase3 within thegeological formation where CO2 is being
injected and must be contained. CO2 that isfully dissolved in water, or otherwisetransformed through chemical reactions istherefore not included in the CO2 plume.

3 Free-phase CO

2 means CO2 in supercritical, gaseous, or liquid phase, rather than as adissolved component in native fluid or otherwise chemically transformed or bonded.

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Guidance document 1

Term

Migration

Leakage

Definition in CCS Directive
Movement of CO2 within thestorage complex.

Any release of CO2 from thestorage complex.

Comments
Movement of free-phase CO2 within thestorage complex.
This refers to CO2 in free-phase, i.e. it does
not include CO2 that has been dissolved inwater, mineralised or otherwise transformed
through chemical reactions. However, theassessment and quantification of leakage
must include the potential for any exsolutionof CO2 from displaced formation fluids outside
the storage complex. Specifically, if CO2
charged water is displaced to the watercolumn, then it will be assumed that the CO2
will eventually come out of solution and countas leakage. This is in accordance with theMonitoring and Reporting Regulations to the
EU Emission Trading System (ETS), Annex
IV, Section 324, which states that a release of
CO2 into the water column must be counted
and quantified as CO2 emissions.
Note: Recital 20 of the CCS Directive covers
enhanced hydrocarbon recovery (EHR)
combined with geological storage of CO2,
where the provisions of the CCS Directive
apply. This means that the release ofquantities of CO2 from surface installations
which do not exceed what is necessary in thenormal process of hydrocarbon extraction,
and which do not compromise the security of
the geological storage or adversely affect thesurrounding environment does not represent
leakage under the CCS Directive.

Significant risk

A combination of aprobability of occurrence ofdamage and a magnitude ofdamage that cannot bedisregarded without calling
into question the purpose of
the CCS Directive for the
storage site concerned.

4 https://eur-lex.europa.eu/eli/reg_impl/2018/2066/OJ.

14

The purpose of the CCS Directive is to enable
environmentally safe geological storage of
CO2 where injected CO2 is permanently
contained within the storage complex while
preventing and, where this is not possible,
eliminating as far as possible the risk ofleakage, and any risk of negative effects tothe environment and human health. The riskof leakage and possible negative local effects
on the environment or human health shouldbe established for each storage site based ona project-specific assessment. Combinationsof probability of occurrence and magnitude ofdamage that can represent a significant risk
will be discussed in sections 4.2 and 4.3.

Guidance document 1

Term

Definition in CCS Directive

Comments
A significant irregularity is a situation that can
result in an event with potential for leakage ornegative consequences to the environment orhuman health. The risk identification should
identify and describe the threats that may
cause significant irregularities, and theassociated risk of leakage or risk to theenvironment or human health.

Significant
irregularity

Any irregularity in theinjection or storage
operations or in the conditionof the storage complex itself,
which implies the risk of aleakage or risk to theenvironment or humanhealth.

Example:-Threats: for instance, poor cement
quality, cement degradation or casing
damage.

-Significant irregularity: loss of wellintegrity.

-

Risk scenario:oThreat → Significant irregularity →Leakage → Negative effects.

It is important to note that a significant
irregularity does not necessarily imply that thelevel of risk for any associated risk scenario issignificant.

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Guidance document 1

Figure 1: Illustration of a storage complex, storage site and surrounding area.

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Guidance document 1

Table 3: Clarification of key non-defined terms used in the CCS Directive.
Term

Surrounding area

Caprock

Articles using terms

Article 4(3) and Annex I

Comments
The term ‘surrounding area’ is thesurface and subsurface area surrounding
the storage complex where leakage ornegative effects on the environment orhuman health are realistically possible. A
risk assessment should be carried out toassess the significance of associatedrisks, and this should inform the design ofthe monitoring of the storage complex
and surrounding environment under
Article 13 of the CCS Directive. The
storage complex and surrounding area
should be specified in the sitecharacterisation under Annex I, andtogether will normally encompass themonitoring area.
A geological formation overlying thestorage reservoir that effectively restricts
upward migration of free-phase CO2. Itshould also restrict the upward flow of
CO2 charged formation fluids if there ispotential for these fluids to create
negative environmental effects or allow
exsolution of CO2. To fulfil the purpose of
the CCS Directive, the caprock shouldhave sufficiently low permeability toensure a ‘permanent containment of CO2
and prevent negative effects and any risk
to the environment and human health’ inthe site and project-specificcircumstances.

Annex I

Note: Brine charged with CO2 will
generally have a higher density than theresident brine. This implies that upward
movement of CO2 charged brine requirespressure differentials sufficient to drive
the flow of brine along upward,
permeable pathways. By contrast, freephase CO2 is buoyant and can move
upward along permeable paths by gravity
forces.

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Guidance document 1

Term

Articles using terms

Comments

Annex I (Step 2.b and 3.i)

In the context of geological storage ofCO2, the term 'seals' is often usedinterchangeably with caprock to mean ageological formation that restricts the
upward migration of free-phase CO2 andCO2 charged formation fluids. In Annex I,
Item 2.b it is used alongside caprock, canbe understood as a secondary caprock,i.e. a geological formation overlying the(primary) caprock that can restrict the
upward migration of any free-phase CO2that has migrated across the primarycaprock. This interpretation applies tovertical seals. Annex I Item 3.i refers to‘lateral and vertical seals’. Lateral seals
can refer to sealing faults, pinch-outs orother geological features that effectively
restrict lateral flows and which may
create compartmentalisation of theavailable capacity within the storage site.

Article 12

Any substances that could be present in
the CO2 stream as a result of being (a)naturally in the source (i.e. coal, gas, oil,biomass, coal-biomass mixtures), (b)picked up in the capture process, or (c)incidentally entrained or intentionallyadded to prevent hazards during thetransport and injection processes.

Permanent containment

Article 1(2) and 18(1)(a)Permanent containment means that
injected CO2 will be effectively trapped bytrapping mechanisms in perpetuity. It
also means that structural, physicaltrapping within storage complex bycaprock and seals should be effective
when CO2 is present in free-phase in thestorage complex. Dissolved CO2 should
not migrate if there is potential for CO2
exsolution prior to mineralisation or
adsorption.

Overburden

Annex I, Step 2.b

The overburden is the lithostratigraphic
volume of rock overlying the storage
reservoir up to the surface or seabed.

Annex II, 1.2

A discrepancy between observed andpredicted behaviour, outside the range of
uncertainty of predictive models. Though
this may require taking additional
monitoring and possibly preventive or
corrective measures, a significant
deviation does not imply that there is asignificant irregularity.

Seals

Incidental associatedsubstances from thesource, capture or
injection process

Significant deviation

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Guidance document 1

Term

Detectable leakage

Financial security

Financial mechanism

Financial contribution

Articles using terms

Comments

Article 18(2)(b)Leakage that can be detected by direct
monitoring observations based on theapproved monitoring plan, or which canbe inferred from modelling that is in linewith monitoring data.

Article 7(10), Article 9(9),Article 11(4), Article 14(3),Article 16(5), Article 17(5),Article 19

The financial instruments or provisions
created to ensure the operator isfinancially able to cover costs associatedwith site operations, closure and postclosure. The competent authority may
draw on this financial security if theoperator defaults or is otherwise unable
to fulfil the permit obligations under the
CCS Directive.

Article 20

A one-time contribution made to thecompetent authority prior to transfer of
responsibility. Once made, the competentauthority can draw on this financial
mechanism to cover monitoring
expenses and potentially to cover othercosts related to the storage site after
transfer.

Article 20

A specific sum made available to thecompetent authority as part of thefinancial mechanism, which is to be
calculated by the competent authority.

3. Main phases and regulatory steps
3.1.

Main phases

Based on the CCS Directive, the life cycle of a CO2 storage project can be subdivided
into six main phases, culminating in five major project or regulatory milestones. Table
describes the role of the competent authorities and the associated activities for regulatory
authorities and operators during these phases and milestones.
Table 4: CO2 storage life cycle framework summary.
Phase/milestone
Phase 1

Assessmentof storage

Competent authority
activities• Member States intending
to allow storage should

5 Duration: these timeframes are indicative only.

19

Key operator activities• Conduct own
assessments of storage

Typicalduration5
0.5-2
years

Guidance document 1

capacity

Milestone 1 Award of
exploration
permitPhase 2

Characterisatio
n andassessment ofstoragecomplexassess the storage
capacity available in the
country and/or region,and promote CCS
deployment, including byawarding exploration
permits.
• Identify the areas
available for storage site
exploration.
• Competent authority
communicates thetechnical requirements
and evaluation criteriathat operator(s) need tocomply with tosuccessfully demonstratetechnical competence.
• Review exploration permit
application(s).
• Award exploration permit,
if required, to meet theconditions for storage
permit under Article 8(1).6• Review storage permit
applications (compliancewith all requirements of
the CCS Directive and ofother relevant EU
legislation7).
• Storage permit
applications and relatedmaterial should be madeavailable to the European
Commission. The
competent authority must
make the draft storage
permits available to theCommission, which may
provide opinions to thecompetent authority on
the draft permit. The
Commission’s opinion is
non-binding, although thecompetent authority
needs to explain any
departures from theCommission's opinions in
the final permit decision.
• Provideguidance/feedback on
acceptable risk levels
based on risk assessment
results and (preliminary)potential, sites andexploration requirements.
• Outline a tentative
development concept.
• Perform an early risk
assessment to feed into
the site feasibility
evaluation. This isnormally done based on
publicly and in-houseavailable data andmodels.
• Prepare exploration
permit application(s).

2-5• Carry out activities toyears
characterise the storage
complex. This includes
dedicated appraisal dataacquisition.
• Define risk evaluation
criteria (see Section 4.2)
and carry out a structured
risk assessment
iteratively to informcharacterisation activities,
address the risks andunderpin the permit
application.
• Select storage site(s) for
further characterisation.
• Specify the development
concept and prepare
project development plansand design, including
plans for monitoring andcorrective measures.
• Carry out anenvironmental impact
assessment inaccordance with Article 5
of Directive 85/337/EEC,
as replaced by Article 5 ofDirective 2011/92/EU.
• Submit storage permit

6 An exploration permit may not be needed in all cases to compile a storage permit application

under Article 7. For instance, the activities required under Annex I can sometimes be
performed under an existing hydrocarbon production license in order to determine whether
the hydrocarbon field can be used as a CO2 storage site. Other cases where activities
required per Annex I can be performed outside an exploration permit may be determined bycompetent authorities.
7 For example, Article 5 of Directive 85/337/EEC, as replaced by Article 5 of Directive

2011/92/EU.

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Guidance document 1

project development plan,
monitoring plan andcorrective measures plan.

Milestone 2 Award ofstorage permit
Development• Approve and award
storage permit(s).
• Oversee baseline
monitoring in line with theapproved monitoring plan.

Phase 3

Milestone 3 Start ofoperations
Phase 4

Operations8• Carry out inspections.
• Approve reporting.
• Approve any updates tomonitoring and corrective
measures plan.
• Ensure necessary
corrective measures are
implemented.
• Carry out periodical
adjustment of financial
security.
Permit withdrawal• The competent authority
has the authority towithdraw the storage
permit. If this occurs, thecompetent authority must
either issue a new
storage permit (to thesame operator or toanother operator) or close
the storage site.

applications inaccordance with Article 7of the CCS Directive.

• Investment decision forstorage project
development.
• Construct facilities anddrill required project wells.
• Remediate existing
infrastructure and wells if
required to meet condition
in Article 4(4).
• Carry out baseline
surveys and pre-injection
monitoring.
• Update sitecharacterisation, risk
assessment and plans formonitoring and corrective
measures.
• Front-end engineering
design.
• Start CO2 injection
operations andmonitoring.
• Carry out injection
operations andmonitoring.
• Carry out reporting.
• Update models as
required, risk
assessment and plans
for monitoring andcorrective measures.
• Take necessary
corrective measures inthe event of leakage orsignificant irregularities.
• Surrender allowances forany emissions from thesite, including leakages,
pursuant to Directive
2003/87/EC.
• Submit updated postclosure plan.

2-4
years

10-30
years

Permit transfer• The competent authority

8 This only covers ‘normal’ operations and not the temporary continuation of operations if the CA

withdraws the storage permit.

21

Guidance document 1

Milestone 4 Closure

Phase 5

Postclosure/pretransfer

Milestone 5 Transfer of
responsibility

may approve, at therequest of the operator
or following permit
withdrawal, the transferof storage permit toanother operator if the
new operator meets thetechnical and financial
requirements ofArticle 8(1)(b), and thenew operator assumes
all responsibilities andobligations of the former
operator in relation tothe operation and/or
closure of the storagesite.
Authorisation of closure
following request from theoperator under
Article 17(1)(b) (Case 1) ora decision to withdraw thestorage permit under
Article 11(3) and to close
the site under
Article 17(1)(c) (Case 2).
Case 1: When a site isclosed following a requestfrom the operator, thecompetent authority is
responsible for:• inspections;• oversight of monitoring
and reporting;• approval of any updates
to monitoring andcorrective measuresplans;• ensuring the necessary
corrective measures are
implemented;• making periodic
adjustments to thefinancial security.
Case 2: When a site isclosed following thewithdrawal of a storage
permit, the competentauthority must take on the
Phase 5 operator activities
in addition to the competentauthority activities for Phase5.
• Approve or provide a
reasoned rejection of therequest to transfer
responsibility, considering
any opinion issued by theCommission. The
Commission’s opinion is
non-binding but thecompetent authority must
explain any departuresfrom the Commission's
opinion in the final
transfer decision.
• Release remaining
financial security after

22• End of injection
operations andcontinuous
operational
monitoring of
injection.
• Partial reclamation of thesite.
• Carry out ongoing
monitoring.
• Carry out reporting.
• Update risk
assessments, models
and plans formonitoring andcorrective measures.
• Take necessary
corrective measures inthe event of a leakage
or significant
irregularities.
• Surrender allowances
for any emissions fromthe site, including
leakages, underDirective 2003/87/EC.
• Remove injection
facilities.
• Perform site sealing.

• Submit transfer report.
• Make financial
contribution available
to the competentauthority (Article 20).
• End of operator
involvement.

5-20 years

Guidance document 1

Phase 6

3.2.

Post-transfer

fulfilling the obligations
under Article 20.
• Accept the responsibility
for all legal obligations
under Article 18(1) on
behalf of the Member
State, and release theoperator from liability
related to theseobligations.
• Long-term stewardship of
the site by Member State.
• Conduct monitoring todetect leakages and takenecessary corrective
measures in the event ofa leakage or significant
irregularities.
• Surrender allowances forany emissions from thesite, including leakages,
under Directive
2003/87/EC.

5-30 years

Interaction between operators and competent authorities

Interactions between operators and competent authorities on risk management will
depend on the stage of the project life cycle. Operators must interact with the competentauthorities in the following circumstances, all of which should be linked to the risk
management framework:●

applying for an exploration permit under Article 5;●

applying for a storage permit under Articles 6-9;●

reviewing the storage permit under Article 11;●

acceptance and control of the CO2 stream composition under Article 12;●compiling and updating the monitoring plan under Article 13;●

reporting under Article 14;●

routine and non-routine inspections under Article 15;●

notifying the competent authority in the event of a leakage or significant
irregularities and implementing corrective measures under Article 16;●

applying for closure of the storage site and updating the post-closure plan under
Article 18; and●transferring responsibility to the competent authority under Article 18.

In all cases, an ongoing and active dialogue between the operator and competentauthority is recommended as the best practice to adopt, including for projects that areoutside the scope of the CCS Directive as per Article 2. The nature and timing ofinteractions related to these activities are likely to vary across jurisdictions and projectspecific aspects.

23Guidance document 1

To provide predictability to operators, the Member States are encouraged to develop
specific guidance on their expectations to operators on the level of interaction for eachof the above circumstances. This includes expectations to the timing and frequency ofinteractions, and the extent of written inputs required. Guidance can include providing astandardised report structure for reports under Article 14, detailing the content to be
included.

4. Risk management approach
4.1.

Key principles

In the context of the CCS Directive, risk management should demonstrate that geologicalstorage of CO2 within a designated storage complex can be or is done safely inaccordance with Article 1(2) and Article 4(4). Risk management should be an ongoingand iterative process throughout the CO2 storage life cycle with the aim of continual
improvement of the risk assessment process. This will involve regular and ongoingassessments of the risks and uncertainties in the geological framework, models andperformance assessments.
Risk assessments should be documented in a traceable and transparent manner, withthe aim to build trust with the competent authorities and other stakeholders that the risk
assessments have been comprehensive and that results are underpinned byscientifically robust analysis. The competent authority can consult risk management
guidance in relevant standards (such as ISO 27914:2017 Clause 6 or DNV-RP-J203
Section 6) for guidance on how to evaluate the comprehensiveness and robustness ofrisk assessments. However, competent authorities should be fully transparent on therequirements that potential operator(s) need to meet. It is therefore recommended thatcompetent authorities publish a detailed list of essential requirements and evaluation
criteria that they will use to review risk assessments, referring to the relevant standards.
This GD 1 covers risks related to scenarios that may lead to a failure to achieve thepurpose of Article 1(2) of the CCS Directive. This means that it covers only
consequences with a potential impact on permanent containment, on human health oron the environment. The impacts of geological storage on human health or theenvironment fall into two broad categories:
1.

local impacts to human health or the environment, and2.

global effects from avoided release of CO2 into the atmosphere.

A key principle of risk management is that the level of risk is reduced as low asreasonably practicable (ALARP). This implies that some risks may be assessed ascontingent acceptable or tolerable if the cost or effort associated with reducing the risk
is disproportionate to the level of risk, and the risk can be maintained at an insignificant
level (see Section 4.3.4).
One important consideration for an ALARP demonstration and the determination of risk
significance is the principle that the risk of negative impacts should not outweigh the24Guidance document 1

positive effects. For CO2 geological storage activities, this implies that the risk of negative
impacts of a project to human health or the environment should not outweigh the
expected benefits to the social good, including from the emission reductions obtained.
Guidance on how to compare positive and negative effects is provided in Section Error!
Reference source not found..
At a high level, storage sites will need to satisfy three main requirements:●

capacity: sufficient storage volume is available or can be engineered to beavailable9;●

integrity: confidence that the site is secure with no significant risk of leakage ormaterial adverse impacts from induced seismicity, ground motion or earth
deformation; and●injectivity: the site has suitable reservoir properties that allow for sustained
injection at required rates into the geological formations without having a negative
impact on the integrity of the storage site.

A core part of risk management for CO2 storage projects is to identify and rank risk
scenarios against these three requirements and to develop and implement risk anduncertainty management strategies to address and manage these risk scenarios.

4.2.

Risk evaluation criteria

In line with ISO 27914:2017, risk evaluation criteria provide the terms of reference
against which the significance of risk is evaluated. For geological storage of CO 2, thesecriteria must be set on the basis of site-specific information and context.
This section outlines guidance on how to draw up risk evaluation criteria for individualstorage projects, with an emphasis on the risk of not achieving the purpose set out in
Article 1(2) of the CCS Directive, i.e. ‘environmentally safe geological storage of CO2 ispermanent containment of CO2 in such a way as to prevent and, where this is notpossible, eliminate as far as possible negative effects and any risk to the environmentand human health’. The focus is exclusively on the consequences related to leakage,
the environment and human health. It does not cover commercial impacts for theoperator, or reputational impacts to either the operator or the competent authority.
Consequences related to the volume of leakage are generally evaluated indirectlyagainst any subsequent impacts on the environment or human health. This should bedone using site-specific considerations. Impacts of leakage on the global environment
9 The capacity of prospective areas for geological storage of CO

2 within storage sites that use
structural trapping can be assessed using the CO2 Storage Resources Management
System (SRMS) methodology developed by SPE. In mineralisation projects, the capacity isassessed by the reactivity of the rock (over time) and the ability of the operation to avoid
CO2 exsolution prior to mineralisation without causing a negative environmental impact.
From a project perspective, the emphasis is generally on verifying sufficient capacity for
project volumes, rather than on estimating the total available capacity of the selectedstorage site. This also entails evaluating the capacity for sustained injectivity, i.e. injection
rates that can be sustained over the planned timeframe for injection.

25

Guidance document 1(less emission reductions) should also be evaluated, but these are normally of lower
significance than the potential subsequent impacts to human health or the local
environmental impacts. In the European Economic Area (EEA), these impacts are also
covered by the EU ETS (Directive 2003/87/EC), since all storage sites are ETS facilities.

4.2.1.

Categories of likelihood

The criteria for assessing the probability or frequency of an undesirable event are often
established by specifying different categories of likelihood10. For each category, thelikelihood is often conveyed in terms of different descriptors. The descriptors may include
quantitative probability or frequency bands, such as between 0.01 and 0.001 probability
that the event will occur in a single year. The descriptors are often supplemented withmore qualitative descriptors to help project developers factor in industry experience andstatistics.

4.2.2.

Categories of consequence – human health

Similarly, the criteria for assessing potential damage to human health as a result of anundesirable event are often expressed as categories of impact. The impact is often
described in terms of the severity of injuries and the number of potential fatalities, andassociated impact on life quality and work performance, e.g. illness, disability or lost
worktime. It can often be useful to describe, for each impact category, a situation thathas the potential to cause the associated impacts. For instance, ‘a moderate CO2 releaseat well site or topside with exposure to fewer than five people, causing respiratory or
temperature-related health effects requiring short-term medical treatment’.
Given the focus on potential for induced seismicity (and associated ground motion), it isrecommended that operators develop one impact example for leakage events and one
impact example for induced seismicity. The latter has the potential to cause annoyanceand possible damage to buildings and infrastructure, which can have knock-on damages
to human health. Fault slip, which leads to induced seismicity, is also a containment risk.
However, the impacts of this should be evaluated by assessing the possible damage
from any leakage and induced seismicity separately, and classifying the resulting impact
by the most severe damage expected to occur from leakage and ground motion.

4.2.3.

Categories of consequence – environment

The severity of environmental impact depends on the size of the area impacted, themagnitude of the damage to the environment in the area (flora and fauna) and thevulnerability of the flora and fauna that are affected. The impact categories tend toinclude descriptors related to each of the above (e.g. an exposure radius with respect tothe size of the area impacted), as well as the timeframe needed for ecological restoration
to return the environment back to its original, pre-event condition, if return is feasible.

10 ISO 27914:2017 defines ‘likelihood’ as ‘chance of something happening, expressed

qualitatively or quantitatively and described using general terms or mathematically, e.g. by
specifying a probability or frequency of occurrence over a given period’.

26

Guidance document 1

As for human health impact, it is often useful to provide descriptors to aid the impact
evaluation process. This can include how judgements should be made between impact
severity for, e.g. medium flux-rate and short-duration leakage events, compared to low
flux-rate, long-duration leakage events. The descriptors should assist the evaluation ofenvironmental effects from each of the main effects to cover in the hazard
characterisation (see Section 4.3.2), i.e. effects from CO2 leakage, intrusion of CO2
charged fluids and mobilised elements, displaced formation fluids, subsurface
compaction and seismicity.

4.2.4.

Assessing the level of insignificant risk

The aim of this section is to provide guidance on when a combination of a probability ofdamage occurring and the magnitude of damage represents a significant risk. It is
common practice in the maturation of CO2 geological storage projects to visualise risk
significance using a risk matrix, where each cell in the matrix represents a degree oflikelihood and consequence. Cells in the matrix are normally coloured to indicate thelevel of significance of risk scenarios placed in that cell, with red often used to indicate
unacceptable risk.
The operator should propose a risk matrix indicating their view of which cells represent
significant and insignificant risk for the project. The operator must then discuss andcalibrate this proposal with the competent authority. To this end, for each likelihood
range, the operator and competent authority should discuss and agree on theconsequence of each severity level (corresponding cells in risk matrix) for human healthand environment that constitute a ‘significant risk’. This should include assessing thenature of the damage to human health or the environment, the risk acceptance criteria
for such damage in applicable regulations and corporate policies, and the benefits of theCO2 storage activity.
Following a ‘project-specific risk assessment’, operators and competent authorities will
also need to decide whether the aggregate risk profile of the project from all project risk
scenarios is acceptable or insignificant. This also implies that the aggregate risk profile
for the project does not outweigh the project benefits. Section 4.2.5 below provides anexample of how to reach this decision. Once the aggregate risk profile has been finalised
and agreed on between the operator and the authority, the operator should develop andimplement an integrated plan for communicating these risks to the communities directly
impacted.

4.2.5.

Example: how to compare the aggregate risk profile with the
expected benefits of the project

Many risk scenarios for CO2 storage projects have a very low likelihood of occurring. For
this reason, it is recommended to compare the risks and benefits by looking at a portfolioof ‘identical’ or comparable projects as follows:1.

carry out a project-specific risk assessment;

2.

draw up the overall risk profile for the project in terms of the risk of leakage
and potential consequences to human health and the environment;27

Guidance document 1

3.

identify the overall benefit of the project in terms of human health and theenvironment, including the benefits in reducing global CO2 emissions;4.

assume that there is a portfolio of, for example, 100 identical or comparable
projects;

5.

assume that each risk scenario identified for the project occurs at theassessed frequency in each individual project, and that the assessed impact
occurs;6.

evaluate the cumulative damage and cumulative benefit from the portfolio ofidentical or comparable projects;

7.

assess whether the potential damage outweighs the benefit or vice versa.

Case: An offshore CO2 storage project is planning to inject 3 million tonnes (Mt) a year
over 25 years, storing a total of 75 Mt CO2. The likelihood that leakage will occur alongeach injection well over the lifetime of the project is assessed to be 1%. If leakage occurs,
the cumulative leakage will be less than 500 tonnes per well. The environmental impact
related to such a release is assessed to be low. No impacts to human health.
In a portfolio of 100 identical or comparable projects, the cumulative planned annual
storage is 300 Mt and the cumulative total storage is 7 500 Mt. This is the key benefit of
the project. The cumulative leakage from the injection wells will be 1 500 tonnes, and thecumulative environmental impact will be low. This is the key negative impact to humanhealth and the environment.
Clearly, in this case, the cumulative benefit of the portfolio outweighs the cumulative
negative impacts. In a real case, one would also need to include an assessment of thenegative impacts of all risk scenarios, not just the risk of leakage from the injection wells.
Nonetheless, this example illustrates how risk and benefits from a particular project canbe made more tangible and understandable for stakeholders by taking the portfolio
approach, i.e. comparing the risks and benefits against a portfolio of identical orcomparable projects.

4.3.

Risk assessment

4.3.1.

General guidanceThis section provides guidance on how to interpret and implement the requirements tocarry out risk assessments as laid out in Step 3.3 of Annex I to the CCS Directive. Thisentails characterising the hazards (Section 4.3.2), assessing exposure and potential
effects (Section 4.3.3) and characterising the risk (Section 4.3.4).
The risk assessment for geological storage of CO2 should be site-specific. This means it
should take into consideration the site-specific context and geological conditions,
including local population density, the nature of the local biosphere and hydrosphere, thenature and magnitude of any scenarios involving dispersal of CO2 to atmosphere or watercolumn, and whether the site is onshore or offshore. The composition of the CO2 stream
should also be factored in.

28

Guidance document 1

For each stage of the life cycle, the starting point would be to review any risk assessment
carried out in an earlier phase of the life cycle. Next, the risks should be assessed in lightof new data and an analysis of the results obtained through the project activities. Any
additional risks that were not previously identified should be considered if the new data
reveals new risks or uncertainties. This process should include a review of the geologicalframework, modelling, the numerical simulations, monitoring results and any otherrelevant data. It should also include consideration of the following questions:●

Does the available geological data and data resolution provide a sufficient basis
for the geological model that gives an adequately correct and detailed
representation of the storage site and its overburden?

●

Are the geological model(s) built and populated with appropriate lithologicalparameters with respect to the decisions to be made?

●Have the dynamic models been properly history-matched and aligned with
monitoring data?

●

Is the current list of possible leakage pathways comprehensive?

●

What is the potential magnitude of leakage events for the leakage risk scenarios
identified?

●Have the critical parameters affecting containment and leakage been duly
considered?

●Have the most relevant secondary effects of the storage project that may havean adverse impact on human health or the environment been considered (seeItems 2-5 in Section 4.3.2)?

●

Are there any other factors that could pose a hazard to human health or theenvironment (e.g. physical structures associated with the project)?

29

Guidance document 1

4.3.2.

Hazard characterisation

Hazard characterisation under Annex I, Step 3.3.1 of the CCS Directive, is synonymouswith risk identification, covered in Clause 6.7.2 of ISO 27914:2017 and Section 6.3.2 of
DNV-RP-J203. Users of this GD 1 are encouraged to also consult these standards for abest practice approach to identifying the risks of projects that involve the geologicalstorage of CO2. The hazard characterisation required by the CCS Directive (Box 2),
however, focuses exclusively on leakage and ‘other factors which could pose a hazard
to human health or the environment’.
Box 2: CCS Directive requirements to hazard characterisation.
Hazard characterisation must be undertaken by characterising the potential forleakage from the storage complex […]. This must include consideration of:a)potential leakage pathways;b)

the potential magnitude of leakage events for identified leakage pathways(flux rates);c)

the critical parameters affecting potential leakage […];

d)secondary effects of storage of CO2, including displaced formation fluids
and new substances created by storing CO2;e)any other factors that could pose a hazard to human health or theenvironment […].

The process of hazard characterisation must cover the full range of potential
operating conditions to test the security of the storage complex.
Local hazards to human health or the environment arise from five principal effects:
1.

Direct effects of leakage, resulting in elevated concentration of CO 2 andimpurities in the CO2 stream composition in the overburden, in theatmosphere or in the water column above a storage complex11. In thissection, leakage pathways are divided into two main categories: geologicalpathways (Table ) and manmade systems (Table ).

2.

Effects of intrusion of CO2 charged fluids and mobilised elements into
groundwater or other environmental receptors in the biosphere12.

3.

Effects from the displacement of formation fluids and mobilised elements by
the injected CO2, including brine (for aquifer storage) and hydrocarbons (forstorage within or below hydrocarbon fields).

11 Anomalies with CO

2 release to seabed or atmosphere can arise from other origins than theCO2 storage site, such as biogenic sources in the overburden.
12 ISO 27914:2017 defines the biosphere as the ‘realm of living organisms including theatmosphere, on the ground surface and in soils, in oceans and seas, in surface waters suchas rivers and lakes, and in the subsurface above the storage complex’.

30

Guidance document 1

4.

Effects of subsurface compaction and corresponding ground displacement(uplift or subsidence).

5.

Effects of natural or induced seismicity and associated knock-on events,
such as damage to wells and to the built infrastructure.

The leakage pathways specified in Table and Table are also relevant to the process ofidentifying risk scenarios for effects 2 and 3 in this list.
The risk identification process should identify threats that can cause any of these effects
to occur, and describe the associated risk scenario, i.e. the threat-event-consequence
sequence. The requirement to characterise each hazard implies that the associated risk
scenarios must also be characterised. Modelling and sensitivity analysis can be used to
identify the risk scenarios and the critical parameters that could result in leakage, or anyof the other principle effects.
For leakage-related risk scenarios, the hazard characterisation requires estimating thepotential magnitude of a leakage (i.e. leakage rates and duration) following various
credible modes of containment failure. While industry statistics may be able to support
characterisation of leakage rates and durations for some risk scenarios (e.g. active
wells), it is likely that the estimation of leakage magnitude for many scenarios will need
to be based on qualitative judgements.
In both cases, it is recommended that the operator estimates the expected or most likely
magnitude in the event of the associated risk scenario. A worst-case estimate of bothrate and duration will generally lead to undue exaggeration of the leakage magnitude.
To capture both the down- and up-side cases and properly reflect the degree of
uncertainty in the estimated magnitude of a leakage, operators are advised to estimate
the uncertainty range for both rate and duration, and to communicate these uncertainty
ranges.
If the geological formation(s) used for geological storage of CO2 is within a hydraulic unitthat is or has been used for other activities, e.g. neighbouring CO2 storage activities,hydrocarbon field developments or geothermal operations, then the operator should
consult with the competent authority to ascertain the nature, extent and duration of suchactivities, and consider the pressure influence from these activities when identifying risk
scenarios. Such influences may impact CO2 storage capacity and associated subsurface
compaction can also impact well and seal integrity. To achieve safe storage in a multisite hydraulic unit, it is important to reach a common understanding of the impact ofpressurisation on critical points in entire hydraulic units, including wells and faults.
The competent authority should therefore enable, and put forward requirements for,sharing related information between operators, and to maintain records of pressure
influence from previous operations. When acreage for CO2 storage is made available inhydraulic units that extend across national borders, the competent authority should
ensure that there is adequate sharing of information between the authorities in therespective countries to inform operational constraints on pressurisation.

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Guidance document 1

Table 5: Potential geological leakage pathways from geological storage sites.
Leakage pathway

Potential leakage mechanisms

Notes

Vertical leakage•
through
caprock13

Through the pore system in the
caprock if the capillary entry pressure
is exceeded, or through existing (high)permeable paths in the caprock.

Dependent on caprock characteristics,
and interplay with CO2 plume build-up in
storage site.

Caprock is locally absent or more
permeable.

Depends on caprock distribution andthickness, including changes to the facies
or erosion. Requires mapping using
seismic and well data.

•

Geochemical degradation of caprock•quality, including any alteration of
permeability along fault zones.

Depends on site-specific geochemistry
and potential reactions between caprock,CO2 stream constituents and formation
fluids.

Vertical leakage•along faults or
fractures

Fracturing of the caprock induced by•injection.

(Relevant for•storage options
that rely on
structural
trapping)

Via faults and/or fractures in caprock•or seals (prior to initiation of CO2
injection).
•

Depends on minimum principal stress incaprock and pressure build-up in storage
reservoir.
Fracturing induces (micro-)seismicity.
Not all faults are potential pathways forleakages. Some are closed or sealed.
Geomechanical or geochemical effects
can create or enhance fault
transmissibility.
Depends on fault and fracture distribution
and characteristics, and the pressure
history of the storage site.

(Relevant forstorage options•that rely on
structural
trapping)•••

Via faults that have been reactivated.•••

Depends on fault and fracture distribution,
characteristics and geomechanics.
Fault reactivation may induce seismicity.
Fault reactivation can occur due toinjection-induced changes in reservoirpressure and temperate or due to natural
seismicity.

Structural spill •Via a spill point (lowest point in•
structure that can provide lateralclosure) if the reservoir is overfilled, •and subsequent vertical or lateralleakage.
•

Depends on site structure, capacity andstorage management.
Can be managed by implementing themonitoring and operating strategy.
Relevant for storage options that rely on
structural trapping.

Lateral leakage •Movement of CO2 outside the lateral•boundary of the storage complex, e.g.
via up-dip migration.
•

Depends on up-dip facies, rock types andpermeability.
Mainly relevant to storage sites that relyon structural trapping, but without
structural closure.
Particularly relevant for sites that rely on
residual saturation trapping.

•CO2 exsolution •Failure of dissolution trapping prior to•mineralisation.

13 See interpretation of term ‘caprock’ in Section 2.4.

32

Relevant to sites that lack seals capableof providing structural trapping of freephase CO2, i.e. sites where containment
relies on effective trapping by othertrapping mechanisms.

Guidance document 1•

The reservoir pressure needs to be
maintained above bubble-point pressure
to avoid exsolution of CO2.

Table 6: Potential manmade leakage pathways.
Leakage pathway

Type ofpathway/mechanism

Notes

Wells and boreholes••

Risk depends on the characteristics of eachwell, including age, status (active, suspended,
abandoned), use (injection, production,
monitoring), construction and abandonment.

•

Risk also depends on the ability to implement
remediation options to (re-)establish wellintegrity in a CO2 storage environment.

•

Well integrity is required for all storage sites,
but the specific requirements to achieve
integrity may depend on storage site options
and local circumstances, e.g. sites where CO2
plumes will exist and sites where all injected
CO2 will be dissolved during the injection
process.

•See GD 2 for further information on evaluating
legacy wells for leakage risk.

Well blow-outs•(uncontrolled
emissions from
drilling and operation •of injection wells).

Likely to be rare as established drilling and welloperations practices reduce risk.

•

Pathways associatedwith mining activity
within or below
storage complex

Operational or
abandoned wells(and boreholes).

•Abandoned mineworkings.

•

Mining-induced
subsidence.

•

Future mining of
CO2 storage
reservoir.

33

Possible source of high-flux leakage during
drilling and injection operations, usually over ashort period of time.

•Blow-outs can be remediated.

•

Largely related to CO2 storage in coal beds.

•

Compaction and subsidence may impact wells
and the built infrastructure overlying areas ofmining activity, and loss of well integrity or fault
reactivation can create CO2 leakage.

•Specific issue for coal bed reservoirs.

Guidance document 1

4.3.3.

Exposure and effects assessment

The exposure and effects assessment under Annex I, Step 3.3.2 and 3.3.3 of the CCS
Directive (Box 3) are elements of risk analysis. The requirements to risk analysis arecovered in Clause 6.7.3 of ISO 27914:2017 and Section 6.3.3 of DNV-RP-J203. Usersof this GD 1 are encouraged to consult these standards for a best practice approach torisk analysis for projects involving the geological storage of CO2.
Box 3: CCS Directive requirements to exposure and effects assessment.
The ‘exposure assessment’ should be based on the characteristics of theenvironment and the distribution and activities of the human population above thestorage complex, and the potential behaviour and fate of leaking CO2 from identified
leakage risk scenarios.
The ‘effects assessment’ should be based on the sensitivity of particular species,
communities or habitats linked to identified leakage risk scenarios. Where relevant,it must include the effects of exposure to elevated CO2 concentrations in thebiosphere (including soil, marine sediments and benthic waters (asphyxiation;
hypercapnia) and reduced pH in those environments as a consequence of leakedCO2). It must also include an assessment of the effects of other substances that may
be present in leaked CO2 streams (either impurities in the injection stream or new
substances formed by storing CO2). These effects must be considered at a range of
temporal and spatial scales, and linked to a range of different magnitudes of leakage
events.
Box 2 focuses on the effects of a leakage. The exposure and effects assessment should,
however, also include an analysis of the exposure and the effects of the other principal
effects listed in Section 4.3.2.
The risk analysis process aims to provide the information required to estimate the levelof risk, i.e. the likelihood that a certain risk scenario can occur, and the magnitude ofdamage that could result if the risk scenario occurs. This step should therefore focus onassessing whether the results from the data collection process and any modelling andsimulation studies performed provide an adequate basis for evaluating the risks anduncertainties. The risk analysis process also involves the deliberation of possible risktreatment options for mitigating the risk, and whether this can be justified given the
additional cost, time required, and other practical aspects involved in mitigating the risk.
The risk analysis process may entail evaluating both the qualitative and quantitative
aspects of leakage, risk significance, and the associated uncertainties. Quantitative orsemi-quantitative risk analysis approaches should be applied to risk scenarios where it
is possible to obtain the relevant data for quantification, e.g. available empirical data,
statistics or scientific reasoning. The latter can involve dedicated modelling studies andevaluating the sensitivity to key parameters. An example where quantitative approaches
may be appropriate are well-leakage scenarios. If data to support a quantitative risk
analysis approach cannot easily be obtained, then the level of risk for associated risk
scenarios should be calibrated by the judgement of experts qualified in terms of theirapplicable professional expertise and project knowledge.

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Guidance document 1

A variety of quantitative estimation methods may be applicable to risk analysis, including
numerical models and analytical models. All methods can be carried out in a
deterministic or probabilistic manner and the underlying assumptions and boundary
conditions must be thoroughly understood before using the results. Similar methods may
be used to assess risks using the following illustrative analysis approaches:●

Scenario analysis: the process of analysing a range of possible future events byassessing alternative outcomes. This may involve constructing a few models thatsatisfy and represent the observed characterisation data to a similar degree andthen comparing the storage performance predicted by each model.

●

Reliability analysis: using methods that aim to estimate the probability of failureof an engineered system given stochastic loads and uncertain characteristics ofthe engineered system.

●

Sensitivity analysis: a quantitative assessment of parameter sensitivity based onmodelling the impact of parameter variations of key uncertain parameters to one
or more performance functions. The emphasis is usually on rigorously ranking
the relative importance of a set of uncertainties.

Judging the likelihood and consequence of risk elements, or the associateduncertainties, both qualitatively or (semi-)quantitatively, depends on the reliability of the
input parameters. Care should be taken to use a valid body of data and experience tojustify the application of quantitative analysis to risk elements affecting the geologicalstorage of CO2.

4.3.4.

Risk characterisation

Risk characterisation under Annex I, Step 3.3.4 of the CCS Directive (Box 3) is often
called risk evaluation. It involves categorising and ranking identified risks using risk
evaluation criteria. Risk evaluation is covered in Clause 6.7.4 of ISO 27914:2017 andSection 6.3.4 of DNV-RP-J203. Users of this GD 1 are encouraged to consult thesestandards for a best practice approach to risk evaluation for projects involving thegeological storage of CO2.
The risk evaluation process is supported by the risk analysis (Section 4.3.3). Risk
evaluation compares the results of a risk analysis against the risk evaluation criteria toascertain whether the risk is significant. The aim of the risk evaluation process is tocharacterise the potential significance of each risk by assessing the likelihood that risk
scenarios can occur and the severity of the consequences that could arise if they occur.
The significance of each risk should then be characterised and placed in one of thefollowing two risk categories:●

insignificant risks: risks that do not call into question the purpose of the CCS
Directive for the storage site concerned; and●significant risks: risks that must be reduced to insignificant by taking risk-reducing
measures in order to meet Article 4(4) and subsequently achieve compliance withthe conditions for transfer of responsibility (to meet Article 18(1)(a)).

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Guidance document 1

Under ISO 27914:2017, the result of the risk evaluation before mitigation sets theperformance requirements for the corresponding strategy for mitigating the risk14, i.e. thelevel of risk that needs to be achieved to be ‘insignificant’. It is considered best practice
to document both the level of risk before implementing risk treatments aimed at mitigating
the risk, the target level of risk to be achieved after the risk mitigation actions are taken,
and to justify why the selected risk controls will be effective in mitigating the risk. The
uncertainty attached to the predicted effectiveness of planned risk mitigation action
should also be evaluated and documented. See Box 4 for guidance on the selection ofrisk controls.
Box 4: CCS Directive requirements to the risk evaluation process.
Risk evaluation must comprise an assessment of the safety and integrity of the site
in the short and long term, including an assessment of the risk of leakage under the
proposed conditions of use, and of the worst-case environment and health impacts.
The risk evaluation must be conducted based on the hazard, exposure and effects
assessment. It must include an assessment of the sources of uncertainty identified
during the steps of characterisation and assessment of storage site and when
feasible, a description of the options to reduce uncertainty.
For many risk scenarios related to the geological storage of CO2, there may be significant
uncertainty related to both probability and severity. This also applies to the risk reduction
effect of the alternative safeguards. The CCS Directive requires consideration of worstcase impacts (Box 3). This can be done by assessing the worst plausible consequencesthat can follow from the risk scenarios. Alternatively, the level of risk can becommunicated using the best estimate, along with the associated uncertainty, forexample by giving a range of possible outcomes. The aim is to be objective and avoid
bias without unduly exaggerating the risk. The risks would then be managed andeffectively downgraded as more knowledge about the sites is acquired and uncertainties
are assessed and reduced.

14 Risk treatment refers to the process of implementing risk controls (safeguards). In line withISO 31000:2018, risk controls are measures that maintain and/or modify risk.

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Guidance document 1

Box 5: Guidance on the selection of risk controls.
Risk controls (safeguards) may be preventive or corrective. Preventive controls canbe implemented to reduce the probability of an incident carrying risk from occurring
or reduce the impact associated with an incident if it occurs. Corrective measures are
safeguards implemented to reduce the consequences from risk scenarios after they
have occurred. The CCS Directive definition is 'measures taken to correct significant
irregularities or to close leakages in order to prevent or stop the release of CO2 fromthe storage complex’.
Safeguards can be natural (inherent), engineered, or operational (procedural). They
may include the consideration and use of multiple storage sites and/or storage targets
within the same storage complex. Figure 2 shows a hierarchy of different types ofsafeguards reflecting the hierarchy of risk control mechanisms that may be applied.
The top three elements of the hierarchy of risk control (eliminate, substitute andisolate/separate) lead to 'inherent safety'. It follows that these three elements of risk
reduction are the most important for CCS projects, and they must be assessed at an
early stage.
Figure 2: Potential hierarchy of control to help compare alternative safeguards
to reduce risk.

The evaluation of more than one storage option ensures that a site with poor lifecycle containment is characterised and 'eliminated' following a proper risk
assessment, and instead a preferred site with a demonstrably secure capacity is
selected. The residual risk features within that preferred site can then be isolated byphysical separation (e.g. by creating a distance between the injection wells from any
susceptible faults and below the caprock).

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Guidance document 1

In addition to a qualitative or quantitative risk ranking based on a risk analysis, the risk
evaluation may involve facilitated sessions with a group of experts that have detailed
knowledge of the storage project. However, experts are biased by their experience. To
reduce bias in risk evaluations, it is important to select a broad group that includes both
representatives from the operator and experts that have no particular stake in the CCS
project. It might also include representatives from the public or the local authorities that
may evaluate certain risks differently to the operator or people with knowledge about thegeologic storage of CO2. One of the aims of stakeholder participation in the risk
evaluation is to enhance transparency around the risks and risk management amongst
groups exposed to risk.
The process of evaluating the risk and selecting risk treatment should form the basis fora dialogue with the competent authorities to ensure that the legal requirements of the
CCS Directive are met. Deciding what constitutes a significant risk versus insignificant
risk is, however, ultimately subjective, and it depends on the risk appetite of the entities
exposed to risk or will bear responsibility for managing the risk.
Therefore, to reach an agreement between the operator and competent authority that astorage site meets Article 4(4) – under the proposed conditions of use there is no
significant risk of leakage, and no significant environmental or health risks exist – it isrecommended that the operator is transparent about the risk controls considered andwhy the chosen risk controls were selected. The operator can then also be requested to
explain why certain risk controls were not selected or considered necessary to reduce
the risk to an insignificant level. Box 5 provides an example of how an operator could set
the stage for a dialogue with a regulator to agree on risk controls to be implemented toestablish that the risk of leakage along an abandoned well is insignificant.
In the process of assessing significant versus insignificant levels of risk, it should behighlighted that such determinations are not necessarily transferable between sites. For
instance, a risk scenario with the same likelihood for leakage to occur, and the samepotential magnitude of leakage, may be found to be insignificant risk at one site andsignificant risk at another site. This is due to differences in negative effects of the leakage
to human health or the environment. Such effects can, for instance, be quite different for
an offshore site compared to an onshore site. Similarly, the significance of an ‘identical’risk scenario related to any of the other effects listed in Section 4.3.2 can be evaluateddifferently for different sites.
It is also important for the operator to consider how the risks and risk profile will evolve
throughout the lifecycle of the storage project. This should include evaluating how theaggregate risk profile from all leakage risk is expected to evolve over time, and thecorresponding effect of risk treatment actions.

38Box 6: Example of how an operator set the stage for a dialogue with competentauthority to agree on level of insignificant risk.
Consider the following situation:
1.

Abandoned well within the permit area in an onshore storage project.

2.

Plume set to intersect the well 10 years after injection.

3.

Comprehensive well records exist from time of abandonment (1982).

4.

Well integrity considered to be good.

5.

The initial views of the regulator and the operator are as follows:

6.

Regulator: all abandoned wells that may be in contact with the plumemust be re-abandoned.

7.

Operator: well will be re-abandoned if leakage occurs.

A number of options are then identified to reduce the risk, as follows:
1.

Re-abandon well.

2.

Monitor well for early signs of leakage – re-abandon if detected.

3.

Monitor well for early signs of leakage – re-design injection strategy if
detected.

4.

Monitor for leakage at surface – re-abandon well if leakage is detected.

5.

Monitor for leakage at surface – assess impact of leakage and redesign
injection strategy. Re-abandon if significant leakage.

Figure 3: Potential risk reduction resulting from the 5 identified options illustratedusing a risk matrix.

The risk reduction potential of the measures is represented in the matrix above. A
dialogue would take place between the operator and the regulator to determine whichof the options should be taken in practice in order to meet the pre-conceived level of
insignificant risk. Note that the result of the dialogue would normally include selection
both of a monitoring strategy for this particular risk (monitoring either the well or thesurface) and of a corrective measure if an adverse event occurs (redesign of injection
strategy, re-abandoning of well). The process would be repeated for all risks that are
not ranked as insignificant pre-mitigation.

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