Risk assessment in geological storage of

CO2

Katriona Edlmann

What is risk management

• A risk is defined as the possibility of non-achievement of objectives (long term CO2 storage) due to uncertainties and threats affecting the storage process.

• Essentially all activities of a storage project involve (different degrees of ) risk

• All aspects of the storage system must manage their risks by identifying the risks, analysing the risks and then evaluating whether the risks should be modified by risk treatment in order to satisfy the risk criteria

• Throughout the risk management process, project managers constantly monitor and review the risks and ensure that the risks are controlled and no further risk treatment is required.

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Risk Definition

• Threat (leakage) quantified by its probability

Event

Risk

• Consequence: technical, financial, environmental, human..

Issues

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Risk management framework

Establishment of the context

Risk identification

Risk evaluation

Action

Risk treatment

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Risk estimation

Risk profile

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RISK ASSESMENT

Risk management workflow

CO2 storage system

Risk Identification

• Risk register

Risk Estimation

• Probability

• Severity

Risk Evaluation

• Risk mapping

• Risk ranking

Risk Treatment

Iterative process

Severity

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Severity

Reduction action n°1

Reductionaction n°2

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Risk estimation tools

Cross-disciplinary expert

workshops / questionaires –

expert elicitation

Subsurface modeling and

probability estimation Statistics

• Use of qualitative (expert elicitation) and statistical analysis

• Quantitative (modeling) and probabilistic tools

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CCS

Diversity of CCS risk

• Industrial risks: CCS capture, transport, storage

• Financial risks: Business or investment-related risks, credit risk, market risk , liquidity risk

• Communication risks: Corporate image

• Security risks: e.g. terrorism

• Natural risks: e.g. eruptions, earthquakes, climate change

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CCS risk uncertainties

• Immature technologies (capture)

• High subsurface uncertainties (particularly aquifers)

• Little industrial feedback: only 3-4 existing

commercial-scale CCS projects

• Integration of components (power plant –> transport

–> storage)

• Public acceptance?

• Economic models?...

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Geological storage risks The subsurface – complex system with high

degree of uncertainty

• Multiple and site-specific subsystems:

wells (injection, monitoring), aquifers,

caprocks, aquitards, freshwater, faults…

• Many interacting components: rock

minerals, CO2, formation fluids,

hydrocarbons under changing pressure and

temperature.

• Various models needed to represent the

THMC system and properly assess the

risks: geological model, reservoir model,

geochemical model, geomechanical

model.

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Primary risks for geological storage

• Loss of injectivity • Loss of capacity • Loss of containment

• Lateral extent of CO2 plume

• CO2 migration through caprock and overburden

• Induced seismicity • Uplift

Risk identification

Thorough identification of the potential caprock leakage

pathways and leakage impact factors – the risks

Site characterisation tool

(to support risk management)

Develop ranked procedure for data collection during site selection, assessment and

operation

Risk estimation

Expert elicitation to assign a severity and timescale of

potential caprock leakage if the risk was not fully characterised

Heletz CO2 caprock leakage Risk management process

Heletz caprock leakage risk study

• This study was undertaken within the EU funded MUSTANG project, looking at a multiple space and time scale approach for the quantification of deep saline formations for CO2 storage.

• Undertaken to investigate the leakage risks for the CO2 injection field site we are using at Heletz and was to be based on the Heletz field data.

• Sadly this data was not available when the leakage risk assessment was undertaken.

• Became a broad overarching look at CO2 caprock leakage risk factors.

• It provides an overview of many of the factors that could potentially contribute to leakage and attempts to assess the potential scale of the leakage.

Leakage pathway

identification

Questionnaire - Expert

elicitation

Leakage risk matrix

Site characterisation

tool

Caprock leakage risk study

Risk Identification CO2 Leakage Pathways

• 44 potential CO2 leakage pathways and leakage impact factors influencing CO2 leakage were identified and categorised into 6 primary categories: – Caprock matrix properties

– Caprock mineral alteration

– Fluids: injected, formation and migrating

– Stress and fracturing

– Wellbore environment

Risk Identification CO2 Leakage Pathways

Risk estimation - Questionnaire

• Methodology: Expert elicitation using a questionnaire

• 14 academic experts in CCS from the MUSTANG project completed a risk assessment questionnaire.

• They evaluated the impact of the severity (extent) and probability (timescale) of CO2 leakage by the identified potential CO2 leakage pathways (risks).

• They evaluated whether each potential risk present a significant CO2 leakage hazard if were not properly quantified.

• No specific field data was provided and the participants were asked to simply assess each risk based on how significant the CO2 leakage could be at maximum for each risk factor.

Expert elicitation

• When eliciting expert opinion, the results must be treated with caution as individuals; including experts, are subject to defined cognitive biases which will affect their judgement in situations of uncertainty.

• These biases are the result of decision making processes based on personal experience and personality that are used to simplify the often multifaceted complex scenarios.

• Types of bias include over-confidence, expert level and motivational bias.

Primary drawbacks

• Not site specific – no Heletz data available at the time

• Not life cycle

• No mitigation actions considered.

• The severity distance value takes no account of caprock thickness, caprock multi layering or proximity to valued subsurface resources.

Risk estimation - severity

1 - CO2 distribution into the first mm of the caprock

2 - CO2 distribution into the first 10 cm of caprock

3 - CO2 distribution into the first meters of the caprock

4 - CO2 distribution into the first tens of meters of the caprock

5 - CO2 distribution above

top caprock

• Severity captures the extent of the potential leakage, would the CO2 be distributed into the first few mm’s of the caprock or would it leak to the surface? A scale of 1 – 5 was used where a low severity value of 1 relates to a low extent of leakage.

SEVERITY

Risk estimation - probability

1 - Leakage happens after

10000 years

2 - Leakage happens after

1000 years

3 - Leakage happens after

100 years

4 - Leakage happens after

10 years

5 - Leakage happens during the injection period

• Probability quantifies the likely time period of the potential CO2 leakage pathway. A scale of 1 – 5 was used where a low probability value of 1 relates to a slow timeframe for the leakage.

PROBABILITY

Risk estimation - expert level

1 – Novice

2 – Limited knowledge

3 – Competent

4 – Knowledgeable

5 - Expert

• A personal Expert level was given by each participant for each risk factor assessed alongside the severity and probability values given. A scale of 1 – 5 was used where 1 is novice and 5 is expert.

CO2 leakage risk matrix 5 Risk levels assigned P

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5 Medium High High Extreme Extreme

4 Medium Medium High High Extreme

3 Medium

low Medium Medium High High

2 Medium

low

Medium

low Medium Medium High

1 Low Medium

low

Medium

low Medium Medium

1 2 3 4 5

Severity

Increasing extent of leakage

Risk Matrix plots

• The risk matrix plots will be presented, broken down into the six primary categories:

– Caprock matrix properties

– Caprock mineral alteration

– Fluids: injected, formation and migrating

– Stress and fracturing

– Wellbore environment

All low medium / medium risks

All low medium / medium risks

All low medium / medium risks

All medium / high risks

All medium / high risks

Either low medium or high risks

Leakage risks

11 high leakage risks were identified: improperly abandoned wells (most significant risk)

poor sealing of the injection well

injection rate and position

hydraulic fracturing

injection pressures

lithological discontinuities in the caprock

fracture density

high permeability lithological conduits in the caprock

caprock and storage reservoir dipping to surface

fracture permeability

fluid pressure changes

Risk matrix findings

• Correlation between severity and probability

• Influence of the risk value on the relationship between severity and probability

• Influence of scale on the leakage risk factors

• Determination of a site characterisation tool

Correlation between severity and probability (timescale)

• As the timescale decreases (increased probability) the severity of the leakage increases.

• This could be the result of a number of processing including:

• Conservative experts: give similar values for probability and severity.

• The impact of calculating arithmetic averages.

• indicates that the highest risk period is during the initial stages

Influence of risk on severity and probability

• For lower risk factors the average severity and probability for each leakage risk factor are similar to each other in that low severity (scale of the leak) corresponds to a low probability (longer timescale of the leak). – This could indicate that if the severity of the leakage is low

the leakage will happen over a longer timeframe.

• For the higher leakage risk factors the severity (scale of the leak) of the risk is generally slightly higher than the probability (timescale of the leak) of the risk. – This could indicate that if the severity of the leakage is high

it will happen over a shorter timeframe.

Influence of risk on severity and probability

Low risk values: severity & probability similar

Higher risk values: Severity higher than probability

Influence of scale of the risk factor on leakage risk

• Geological storage risk assessment involves data input from a range of scales:

mm km 100km microns m

Influence of scale of the risk factor on leakage risk

• The results indicate that small scale (pore scale) risk factors have a

lower risk categorisation and that large scale (field scale) factors have higher risk factors.

• The implication is that when constructing the CO2 storage site model the field scale geology and fracture networks must be very well constrained from the beginning of the CO2 storage characterisation.

Risk category Primary classification category Scale

Low medium / medium

Caprock matrix properties Caprock mineral alteration Fluids – injection, formation & migrating

Pore scale

High Stress / fracturing Well environment Geological architecture

Field scale

Site characterisation tool • Ranking the risk data from the risk matrix plot facilitates the

generation of a site characterisation tool that highlights areas where data collection and monitoring should be of high priority if potential leakage of CO2 through the caprock is to be minimised at both the site characterisation and initial operation stages of the CO2 storage process.

• The ranked risk tool is the first stage of the full risk mitigation plan and assists the risk manager / project manager to define the risk mitigation plan to decrease risks or lower uncertainty (especially for high risks).

• The tool supports decision making process for characterisation and monitoring to provide guidance on where the maximum data collection effort should be put.

• In practise site specific data will have to be considered to make site specific recommendations such as monitoring, investigation, analysis, modelling.

Ranked

risk

Identified leakage pathway or leakage

risk factor (risk)

Data required

High risk factors – these have a high risk of contributing to significant CO2 leakage at surface which will impact on both the

environment and communities. 1 Check for improperly abandoned wells (most significant risk) Pressure test abandoned wells in the storage area

2 Lithological discontinuities in the caprock Geological model (and analogue studies) of the interlayered caprock system from seismic and well to well

correlation to assess caprock continuity.

3 Fracture density Detailed fracture mapping of caprock from seismic, downhole and analogues.

4 High permeability lithological conduits in the caprock Geological model (and analogue studies) of the interlayered caprock system from seismic and well to well

correlation to identify any high permeability lithology within the caprock.

5 Caprock and storage reservoir dipping to surface Geological model of the whole storage system from seismic and well to well correlation to assess caprock

and reservoir formation does not dip to surface, even underwater

6 Fracture permeability Fluid pressure tests along fractures that intersect existing wells

Medium risk factors – these have a moderate influence on contributing to CO2 leakage at the surface which will impact on

the environment. 7 Caprock mechanical properties Mechanical testing of downhole and representative caprock core samples

8 Stress field orientation Determination of the storage site stress field

9 Fracture aperture Data on the fracture apertures – this can be generated in conjunction with fracture pressure tests

10 Caprock matrix compressive strength Mechanical testing of downhole and representative caprock core

11 Reservoir rock unconsolidation / collapse Mechanical testing of downhole and representative reservoir core

12 Caprock capillary entry pressure Caprock capillary entry pressures for formation waters and CO2 under reservoir temperatures

13 Matrix total porosity Caprock porosity measurements from downhole and representative caprock core

14 Clay mineral shrinkage Detailed analysis of caprock chemistry from downhole and representative caprock core

15 Mineral dissolution Detailed analysis of caprock chemistry from downhole and representative caprock core

16 Wettability Caprock wettability for formation waters and CO2 under reservoir temperatures

Medium low risk factors – these have a low impact on contributing to CO2 leakage.

17 Matrix permeability Caprock permeability measurements from downhole and representative caprock core

18 Pore compressibility Pore compressibility measurements from downhole and representative caprock core

19 Matrix anisotropy Horizontal and vertical permeability measurements from downhole and representative caprock core

20 Caprock relative permeability to CO2 Caprock relative permeability measurements with formation waters and CO2 on downhole and

representative caprock core

21 Interfacial tension Interfacial tension measurements with formation waters and CO2 on downhole and representative

caprock core

22 Geothermal gradient Detailed log of the borehole and formation geothermal gradient

23 Mineral precipitation Detailed analysis of caprock and formation fluid chemistry from downhole and representative caprock

core

24 Pore / pore throat size Caprock pore distribution measurements from downhole and representative caprock core

25 Thermal conductivity Caprock thermal conductivity measurements from downhole and representative caprock core under

reservoir temperatures and pressures.

26 CO2 sorption Subsurface mapping of organics

27 Electrostatic interfacial repulsion Caprock electrostatic interfacial repulsion measurements from downhole and representative caprock

core under reservoir temperatures and pressures.

Ranked risk

Identified leakage pathway or leakage risk factor (risk)

Data required

High risk factors – these have a high risk of contributing to significant CO2 leakage at surface which will impact on both the environment and communities. 1 Check for improperly abandoned wells (most significant risk) Pressure test abandoned wells in the storage area

2 Lithological discontinuities in the caprock Geological model (and analogue studies) of the interlayered caprock system from seismic and well to well correlation to assess caprock continuity.

3 Fracture density Detailed fracture mapping of caprock from seismic, downhole and analogues.

4 High permeability lithological conduits in the caprock Geological model (and analogue studies) of the interlayered caprock system from seismic and well to well correlation to identify any high permeability lithology within the caprock.

5 Caprock and storage reservoir dipping to surface Geological model of the whole storage system from seismic and well to well correlation to assess caprock and reservoir formation does not dip to surface, even underwater

6 Fracture permeability Fluid pressure tests along fractures that intersect existing wells

Medium risk factors – these have a moderate influence on contributing to CO2 leakage at the surface which will impact on the environment. 7 Caprock mechanical properties Mechanical testing of downhole and representative caprock core samples

8 Stress field orientation Determination of the storage site stress field

9 Fracture aperture Data on the fracture apertures – this can be generated in conjunction with fracture pressure tests

10 Caprock matrix compressive strength Mechanical testing of downhole and representative caprock core

11 Reservoir rock unconsolidation / collapse Mechanical testing of downhole and representative reservoir core

12 Caprock capillary entry pressure Caprock capillary entry pressures for formation waters and CO2 under reservoir temperatures

13 Matrix total porosity Caprock porosity measurements from downhole and representative caprock core

14 Clay mineral shrinkage Detailed analysis of caprock chemistry from downhole and representative caprock core

15 Mineral dissolution Detailed analysis of caprock chemistry from downhole and representative caprock core

16 Wettability Caprock wettability for formation waters and CO2 under reservoir temperatures

Medium low risk factors – these have a low impact on contributing to CO2 leakage.

17 Matrix permeability Caprock permeability measurements from downhole and representative caprock core

18 Pore compressibility Pore compressibility measurements from downhole and representative caprock core

19 Matrix anisotropy Horizontal and vertical permeability measurements from downhole and representative caprock core

20 Caprock relative permeability to CO2 Caprock relative permeability measurements with formation waters and CO2 on downhole and representative caprock core

21 Interfacial tension Interfacial tension measurements with formation waters and CO2 on downhole and representative caprock core

22 Geothermal gradient Detailed log of the borehole and formation geothermal gradient

23 Mineral precipitation Detailed analysis of caprock and formation fluid chemistry from downhole and representative caprock core

24 Pore / pore throat size Caprock pore distribution measurements from downhole and representative caprock core

25 Thermal conductivity Caprock thermal conductivity measurements from downhole and representative caprock core under reservoir temperatures and pressures.

26 CO2 sorption Subsurface mapping of organics

27 Electrostatic interfacial repulsion Caprock electrostatic interfacial repulsion measurements from downhole and representative caprock core under reservoir temperatures and pressures.

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Risk assessment in geological CO2 storage

The use of a formalized risk assesment approach is essential to:

Establish a reliable basis for decision making

Promote proactive rather than reactive management of the CO2 project

Establish a solid, systematic and accepted method for performance-based management of CO2 projects

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Risk Assessment

Provides an overview of technical and non technical risks (e.g. financial, project management, ...) and their changes over project lifetime

Risk ranking

Objective elements for decision making support

Safety demonstration Risk Management

Promote proactive rather than reactive management

Action plan for risk mitigation of critical risks

Overview on potential benefits associated to decisions (cost / benefits analysis)

Sustainable performance Risk Communication

Decision making support, budget support

Stakeholders and Top management

Regulators

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Risk assessment in geological CO2 storage

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