Module 9 Risk management, measurement, monitoring and verification in CO2 storage projects

Original text: R.J. Chalaturnyk & W.D. Gunter, APEC Capacity Building in the APEC Region,Phase II.

Revised and updated by CO2CRC


When a CO2 storage project is being proposed, measurements are taken for site characterisation and the risks are assessed. The scientific methods used for site characterisation are also applicable to monitoring the storage site during various stages of the project. A comprehensive measurement, monitoring and verification plan forms part of and contributes to a risk management program and to demonstrating that a CO2 storage project is meeting its objectives and complying with the regulations in place.

Learning objectives

By the end of this module you will be able to:

  • Be familiar with the concept performance assessment for CO2 storage projects;
  • Be familiar with risk assessment for geological storage projects;
  • Be familiar with stages in a CO2 storage project and the type of monitoring for each stage;
  • Be familiar with monitoring techniques; and
  • Know where to go to for detail on the topic of risk assessment and monitoring and verification.


Performance assessment refers to the process of evaluating the behaviour or performance of an element of a geological storage project relative to one or more performance standards. Performance incorporates both engineering and safety aspects into the assessment. Thus, performance is essentially the ability of the reservoir to retain stored CO2 over time.

In order to assess such performance, the long-term fate of CO2 initially injected into a geologic formation must be determined. Ultimately, if the CO2 migrates far enough to reach the biosphere, but the flux of CO2 to this environment is sufficiently low comparison to an acceptable flux performance standard, it does not pose a potential safety hazard.

Performance assessment forms a key component of a risk assessment for any geological storage project and ultimately feeds into the entire risk management process. In some processes such as EOR, there are elements of the performance assessment that are not contained in the risk management process. Prior to discussing some specific details of the performance assessment process, it is important to review the risk management process as it pertains to geological storage projects.

Risk management provides a comprehensive decision-making process that aids decision-makers in identifying, analyzing, evaluating and controlling all types of risks, including risks to health and safety. The objective of risk management is to ensure that significant risks are identified and that appropriate action is taken to minimize these risks. Such actions are determined based on a balance of risk control strategies, their effectiveness and cost, and the needs, issues and concerns of stakeholders. Communication among stakeholders throughout the process is a critical element of this risk management process. Decisions made with respect to risk issues must balance the technical aspects of risk with the social and moral considerations in the project.

Figure 9.1: Risk management decision making process (after CSA, 1997).

Figure 9.2: Risk management process (after HB 436:2004.)

The region outlined within the dotted line in Figure 9.2 generally describes the activities associated with performance assessment within the context of a full risk assessment.

Establishing the context for the performance assessment

The first step in a performance assessment should define the basic parameters within which the performance assessment should be conducted. These are the administrative details of the process and involve defining the:

  • Organizations or groups involved (stakeholders) and the processes to be followed for the performance assessment;
  • Performance assessment team which provides technical expertise and advice to decision makers. As such, this team is best formed from a multidisciplinary group of experts with specific knowledge and experience concerning the storage project currently being examined; and
  • Scope of the performance assessment. This should include descriptions of the storage project; the potential areas of risk associated with the storage project; decisions that may have to be made;stakeholders who may be affected by the project; and the risks and any assumptions that will be adopted at the outset of the performance assessment. This must include a description of the spatial extent of the storage project that will be assessed, as well as the timeframe of the assessment.

For geological storage projects, the most crucial components of performance assessment are (Wildenborg at al, 2004):

  • Assessment criteria: quantitative criteria that relate to acceptable levels of CO2 exposure and acceptable consequences for health, safety and environment. Examples are: the maximum acceptable CO2 concentration, heavy metal concentrations, or the maximum individual lethality risk;
  • Storage concept: a clear description of the concept of underground CO2 storage must be provided; and
  • Setting of the storage site: this involves a detailed description of the geological and geographical setting of the storage system including previous underground human activities in the area.

Perhaps the most difficult task among these components, a priori, is the establishment of the criteria against which the assessment results will be evaluated. To illustrate, wells (either injection or production) represent a subset or subsystem within the geological storage project that must perform satisfactorily. However, there must be criteria in place to assess the wellbores' performance. Experience in the oil and gas field demonstrates that most wells perform well during their operational life (10 to 15 years). For geological storage, satisfactory performance is required not only over the operational life but over much longer timeframes (in the order of 100 to 5,000 years). Current research and field demonstration activity on measurement, monitoring and verification is focussing much of their activities to assist in the establishment and assessment of these criteria.

Bowden and Rigg (2004) conducted a risk assessment study to assess reservoir risk in CO2 storage projects in Australia as part of the GEODISC project. For the technical assessment context, their study included both containment issues (the ability of the reservoir to contain most of the injected CO2) and effectiveness issues (the ability of the reservoir to receive the planned CO2 injection volumes). Their risk assessment criteria, which could be helpful as a guideposts for future assessments, was:

  • A 99% chance that the total injection will be held within the system for 1000 years;
  • Acceptable containment will be achieved, if one can be 80% confident that 99% of the injected mass will be contained within the system for 1000 years; and
  • It would be acceptable if there was less than a 20% chance that a reduction and/or delay of CO2 mass stored within a geological storage site would result in a zero or negative net greenhouse value.

For each geological storage project, the performance assessment team would be required to develop these types of criteria for evaluating the performance assessment results.

The methodology used by Bowden and Rigg to undertake and qualitative risk assessment by use of an expert panel to establish the likelihood and consequesnces of risks has been also applied to the Weyburn-Midale project. (Preston et al, 2009).

Wildenborg et al. (2004) have developed a methodology for risk assessment of CO2 storage that consists of three major steps, scenario analysis, model development, and consequence analysis, Figure 9.3. Performance assessment is embedded into this methodology. This method is based on risk assessment studies on the storage of radioactive waste, but it has been adapted to the particularities and challenges that geological storage present.

Figure 9.3: The scenario approach for safety assessment (from Wildenborg et al., 2004)

CO2 storage risk assessment methodologies include RISQUE, Structured What if Technique (SWIFT), Screening Risk Assessment (SRA) and TESLA (a decision making tool).

Identify the risks

For most current geologic storage projects, risk identification has been completed following a systems analysis approach. This approach recognizes that a geologic storage project includes several systems -wells, reservoir, surface facilities and others, which interact with each other. Systems analysis consists of several inter-related elements:

  • Development of a list of features, events and processes (FEPs) which together describe the geological storage system;
  • Identification of how FEPs interact within the geological storage system;
  • Construction of scenarios which describe the most likely set of FEP interactions; and
  • Description of how these interactions will be accommodated in the performance assessment modeling to be undertaken for each scenario.

Each of these will be described in more detail below.

Development of a list of features, events and processes (FEP) for geological storage

Features, events and processes can be described in the following way:

  • Features are physical characteristics or properties of the system such as lithologies, porosity, permeability, wells, faults and nearby communities;
  • Events are discrete occurrences affecting one or more components of the system, such as earthquakes, subsidence, drilling, borehole casing leak and pipe fracture; and
  • Processes are physico-chemical processes often marked by gradual or continuous changes that influence the evolution of the system such as precipitation of minerals, groundwater flow, CO2 phase behaviour and corrosion of borehole casing.

A European Commission funded study conducted as part of the Weyburn CO2 Monitoring and Storage Project (Maul et al, 2004) has developed an online FEP database specifically for geological storage projects. The database is internet-enabled incorporating hyperlinks to other relevant sources of information (reports, websites, maps, photographs, videos, etc.), and is searchable in a variety of ways. It includes FEPs relevant to the long-term safety and performance of storage systems after injection of CO2 has been completed and the injection boreholes have been sealed. Some FEPs associated with the injection phase are nevertheless considered where these could affect long-term performance. For any particular geological storage system, it can be utilized to identify an applicable, comprehensive list of FEPs. Moreover, the development of this lists can drawn a vast amount of information from natural analogues such as natural CO2 reservoir, and industrial analogues such as deep injection of wastes, or underground gas storage.

Classification of FEPs

The assessment context for the performance assessment helps to determine which FEPs need to be considered in an analysis and which can be considered irrelevant to the scope of the assessment in a given specific project. To provide a sense of the character of the FEPs identified for a geological storage project, Figure 9.4 provides a list of FEPs developed for the IEA Weyburn CO2 Monitoring and Storage Project (Stenhouse and Zhou, 2001).

Utilizing the definition of the storage system set out in the assessment basis or context, the FEPs are ranked and screened in order to identify the FEPs that are likely or very likely to occur. These FEPs are grouped and assigned to specific zones within the geological storage system (compartments). A combination of interrelated events and processes for a group may include (Wildenborg et al, 2004):

  • The integrity of the reservoir, seal, fault and well completions;
  • The migration of CO2 through the overburden; and
  • Health, safety and environmental impacts in the shallow subsurface or atmosphere.

Figure 9.4: Examples of features, events and processes associated with a CO2–EOR project(after Stenhouse, 2001).

Scenario development

Scenario development is concerned with the identification, broad description and selection of potential futures relevant to performance (and safety) assessment of the geological storage site. Scenario development includes the identification of relevant FEPs, synthesis of broad models of scientific understanding and selection of calculational cases to be performed. Scenarios provide the structure for discussing the likelihood and consequences of CO2 leakage from a storage reservoir and the framework for presenting any biases or shortcomings in the performance (and safety) assessment. Guidelines for Carbon Dioxide Capture, Transport and Storage (World Resources Institute, 2008), contains a set of possible risk scenarios together with mitigation/remediation options.

In general, experts begin with gaining knowledge of how the system has evolved in the past and then determine how the system might operate in the future if not disrupted. After this, they then consider the likelihood and consequences of different perturbations and disruptions. Expert judgment will also make use of the goals and objectives of the risk assessment, and, especially, current modeling capability and data availability.

Based on the above, the next step for geological storage projects is the development of different, plausible and credible ways in which the geological CO2 storage system might evolve over decades to hundreds to thousands of years. These scenarios essentially explore "what if… ?" type questions.

Scenarios are the starting points for the development of conceptual physical/chemical models for which performance assessment analyses are conducted. In identifying possible scenarios, it is generally accepted that there is one most likely way in which the geological storage system would be expected to evolve. This is generally referred to as the Base Scenario. The Base Scenario is defined as the expected evolution of the system being assessed while recognizing that there will be uncertainties associated with this Base Scenario. These uncertainties are typically explored using variants of the Base Scenario called Alternative Scenarios.

The following describes some issues associated with scenario development:

  • Challenges in making predictions about the future behaviour of humans interacting with the storage site;
  • Confidence concerning the longevity of expert consensus views;
  • Estimates of probability; and
  • Possible omissions in FEP lists.

As an illustration, the base scenario and alternative scenarios developed for the IEA Weyburn CO2 Monitoring and Storage Project are presented in Figures 9.5 and 9.6 respectively.

Base Scenario

  • System model domain: the Weyburn 75 well patterns and a 10-km zone surrounding it.
  • Time frame: inception of EOR using injected CO2 and with an nominal end time taken as the earlier of 5000 years or the time at which there is 50% loss (to the biosphere) of CO2 that was in place within the geosphere at the end of EOR.
  • The caprock may have natural fractures or discontinuities but all are isolated or sealed such that caprock integrity is not impaired.
  • There are a series of aquifer/aquitards above and below the reservoir horizon. These media may contain fractures and fissures.
  • Will consider physical trapping features, which have naturally contained the oil/gas within the reservoir.
  • Will consider geochemical effects (formation of carbonate minerals and CO2 removal by solubility and ionic trapping) in the aqueous phase of all aquifers.
  • The biosphere starts from the deepest possible potable aquifer and technically includes all of the glacial till and surficial deposits (i.e. it extends to a depth of about 300 m below ground surface). It includes soil, surface water, atmosphere, flora and fauna.
  • Includes the presence of all wells found within the system model domain.
  • All wells assumed to have been abandoned following current field abandonment procedures applicable at the time of abandonment. Note that this includes wells that may have been sealed in earlier years according to different abandonment procedures and regulations.
  • Well seals may degrade after abandonment. Well seals are primarily the cement used to fill the annulus between the casing and borehole, cement and metallic plugs used to fill the casing bore, and the cap welded onto the casing approximately 4 m below ground surface. Consideration should also be given to degradation of the casing itself within the reservoir and all aquifers and aquitards penetrated by the casing.
  • The base scenario includes consideration of FEPs that could affect the storage and movement of CO2. These include, but are limited to, processes such as hydrodynamics, geochemistry, buoyancy and density driven flow, dissolution of CO2 in water and residual oil, and pressure-temperature changes occurring within the geologic formations.

Figure 9.5: Elements constituting the Base Scenario definition (after Jazrawi et al., 2004).

Figure 9.6: Alternative Scenario descriptions developed for the Weyburn CO2 Monitoring and Storage Project (after Jazrawi et al., 2004)

Guidelines for Carbon Dioxide Capture, Transport and Storage (World Resources Institute, 2008), contains a set of possible risk scenarios together with mitigation/remediation options for a CO2 storage project. The list deals with leakage through faults, fractures, spill points and well, leakage into the soils and groundwater and surface water, CO2 accumulating in indoor environments and large releases to the atmosphere.

Analyze performance

Based on the scenario development and the features, events and processes included in these scenarios, an analysis strategy must be chosen to establish the likelihood of exceeding criteria established in the assessment context stage. This is a critical step in analyzing the geological storage site performance. The choice of analysis method will reflect the accuracy needed (in the results), cost, available data, level of expertise on the team and the acceptability of the analysis method to the stakeholders. The analyses may be qualitative, semi-quantitative or quantitative or a combination of these, depending on the circumstances.

Current performance analysis uses numerical modeling to provide a forecast of the behaviour of scenarios. The results, although in essence quantitative, can be used both in a quantitative or qualitative manner depending on the certainty about the model itself and its parameters. This modeling exercise not only provides a forecast, but also helps to better understand what FEPs are critical to the successful development of the project, as well as helping to identify uncertainties in both FEPs and scenarios.

Qualitative analyses use words to describe the magnitude of potential consequences and the likelihood that those consequences will occur. For geological storage projects, qualitative analyses serve well as an initial screening activity to identify risks which require more detailed analyses. Expert opinion and judgment are important ingredients of qualitative studies. They ensure that all pertinent guidelines, environmental risk indices, and processes have been addressed, and can assist in recommending appropriate comparative guidelines when specific data are unavailable. Moreover, the knowledge and experience of experts have a major influence on the quality of the assessment and on the real and perceived confidence in the results. This last factor actually applies to all risk assessment methods, and can be one of the most important considerations for assessments that are sensitive to members of the public. Qualitative methods for analyzing performance include evaluation using multi-disciplinary groups;specialist and expert judgment; and structure interviews and questionnaires.

In semi-quantitative analysis, qualitative scales are given values, as illustrated in Figure 9.7. The objective is to produce a more expanded ranking scale than is usually achieved in qualitative analyses. Care must be taken with the use of semi-quantitative analyses because the numbers chosen may not properly reflect relativities and this can lead to inconsistent, anomalous or inappropriate conclusions (HB 436:2004). These can also be used as an initial screening tool. Figure 9.7 provides consequence tables and likelihood tables used in assembling the results into an estimate of the risk for any particular scenario chosen for the geological storage project.

Quantitative analyses adopt numerical or analytical models to quantify both consequence and likelihood. In general, this has been the method adopted for most early risk assessment studies for geological storage projects. Performance assessments conducted in the IEA Weyburn CO2 Monitoring and Storage Project adopted both deterministic and probabilistic methods. A sophisticated reservoir simulator was utilized for deterministic analyses and an analytical model was constructed to permit probabilistic performance analyses to be conducted. The quantitative approach can use both natural and industrial analogues as a tool to validate both the numerical and analytical models to be used. Such validation is a fundamental step whenever new approaches are being taken and/or the experience with certain analytical methods is limited and the confidence in them not very high.

For deterministic performance assessments, single point estimates for each parameter are used in the analyses. In contrast, a probabilistic performance assessment generates a coherent set of consequence estimates that reflect the effects of parameter uncertainty. As in the deterministic assessment, a set of parameter values is passed to the computational model, which then generates an estimate of consequence. However, this simulation process is repeated, often thousands of times but with different sets of parameter values.

Figure 9.7: Semi-quantitative analysis categories for the combination of consequence and likelihood,which defines levels of risk.

Quantitative methods employed in performance (risk) assessment include (HB 436:2004):

  • Consequence analysis;
  • Statistical analysis of historical data;
  • Fault-tree and event-tree analysis;
  • Influence diagrams;
  • Simulation and computer modeling;
  • Statistical and numerical analysis; and
  • Probability analysis.

Measurement, monitoring and verification

Measurement, monitoring and verification (MMV) activities provide the confidence that CO2 has been injected and stored in an environmentally sound and safe manner. It also provides verification to both numerical modeling and performance assessment and provides the necessary accounting metrics for emissions trading scenarios (such as those under the Kyoto Protocol) based on geological storage.

The following terms are important to the discussion on monitoring the fate of injected CO2:

  • Migration - refers to movement of fluids (including injected CO2) within the injection formation. This can involve movement both vertically and horizontally within the designated injection horizon. The fluids remain "trapped" by both the upper and lower bounding seal layers;
  • Leakage - refers to movement of fluids (including injected CO2) outside the injection formation. This can involve movement through the upper and lower bounding seals or through wellbore pathways. Leakage includes all pertinent pathways through the geosphere. Monitoring for leakage is important as it includes all processes leading to CO2 movement towards and possibly into the biosphere; and
  • Seepage - refers to movement of fluids (including injected CO2) from the geosphere to the biosphere. Monitoring programs aimed at seepage processes are primarily focused on limiting any health, safety or environmental issues.

CO2 storage projects are generally considered in four phases. These phases are referred to in new and developing legislation for CCS:

  • Pre-operation phase- design, site characterisation, establishing baseline monitoring conditions, risk identification;
  • Operation phase- CO2 injection;
  • Closure phase – Period after injection has stopped and when wells are abandoned, facilities removed and site remediated while monitoring continues; and
  • Post-closure phase – Ongoing monitoring takes place until no longer required (the site is stable). (DOE, 2009).

(Note: The last two phases are also called the "Post-operational phase")

The monitoring required at each phase varies and each project will have specific monitoring programs to reflect the project's geology and objectives. Appendix 1 outlines a methodology for planning a monitoring program.

A monitoring program covers three monitoring domains:

  • The sub-surface domain (the reservoir);
  • The near-surface domain (shallow zones and soil); and
  • The atmospheric domain.

Figure 9.8: Monitoring domains (courtesy of CO2CRC).

The first two domains (subsurface and near-surface) involve monitoring using information obtained from fluid sampling and geophysical sensing in addition to remote monitoring from the surface or related boreholes.

The monitoring in the pre-operation phase is known as baseline monitoring. It establishes the initial condition of the storage system and the environment surrounding the storage site.

Monitoring during the operational phase of the project records the dynamic behaviour of the CO2 as it is injected and within the reservoir. Measurements include surface and downhole pressures, flow rates and the geochemical profile of the injected fluids. Together with tracer sampling, seismic surveys, and well log data, these measurements verify and update the pre-injection models used to predict the behaviour of the CO2 within the reservoir. Atmospheric, groundwater and soil samples are used to monitor the local environment for seepage that could pose a health, safety or environmental risk.

Monitoring technologies

Many of the technologies for monitoring a storage project have been used by the oil and gas industries and are being adapted for CO2 storage. Many of techniques are used for site characterisation, and the data obtained is used for design of the project, for identifying risks and providing the baseline measurements. New techniques, applicable to environmental programs (air, soil and water sampling), are also being adapted for use in CO2 storage projects.

Geophysical and remote sensing uses seismic, electromagnetic, gravity, microseismic and displacement sensors and petrophysical logging measurements.

One of the most common methods used is seismic monitoring. It is used to detect subtle changes associated with the presence of the injected CO2 and map the migration pathways.

Surface seismic monitoring maps the migration path of CO2 plume from injector to producer. The initial surveys carried out before injection need to be repeated during and after the CO2 injection to show the distribution of carbon dioxide over time.

Vertical Seismic Profiling (VSP) provides a high resolution geological image in the immediate vicinity of the boreholes. Seismic sources are located at the surface and receivers are positioned in the boreholes.

High Resolution Travel Time seismic enables monitoring of fine changes in fluid level and can verify the volume of CO2 injected.

Microseismic surveys are used to monitor for fractures or fault reactivation as a result of the injection of CO2.

Figure 9.9: Typical arrangements for vertical seismic profiling (VSP) (courtesy of CO2CRC).

Figure 9.10: A field view of a seismic survey underway at the CO2CRC Otway Project (courtesy of CO2CRC).

Gravity measurements have been used to monitor CO2 movement in the Sleipner project. These measurements show changes in density in a vertical column of rock and can detect the displacement of saline water by CO2.

A recent development in remote monitoring is satellite air-born radar interferometry (InSAR) which detects subtle ground deformation above the injection wells. This technology has been used to determine the level of uplift of the surface in the In Salah CO2 injection areas. This surface uplift is around 5mm/year. (Ringrose et al, 2009).

Geochemical monitoring involves geochemical analysis of fluids, gases, rock/soil, groundwater, surface water and the atmosphere.

CO2 in the injection stream can be tagged using chemical tracers in order to verify the plume behaviour. Water levels and the chemistry of shallow aquifers can be monitored to detect any injected CO2 leakage into these aquifers. Seasonal variation, flow rate and direction of water flows are recorded from deep water bores. Groundwater sampling using a low flow pump will help to detect any chemical changes in the unlikely event of CO2 leakage. High quality well bore fluid and gas samples can be collected at reservoir pressure from multiple levels in a monitoring well and analysed for their chemical and isotopic composition to detect the CO2 arrival.

Figure 9.11: Soil gas sampling at the CO2CRC Otway project (courtesy of CO2CRC).

Environmental sensing techniques include atmospheric gas detection and dispersion modelling, remote sensing techniques including multi spectral analysis

Atmospheric stations can continuously measure concentrations of CO2. A CO2 flux tower can continuously measures surface-air CO2 movement. Soil CO2 flux measurements can be taken at many locations in the project area. Measurement of tracers and isotopes can establish the origin of CO2 emissions to the local atmosphere quantify emissions.

Figure 9.12: CO2 flux station (courtesy of CO2CRC).

Project monitoring and verification results help to confirm the modelling predictions that there is no migration of CO2 beyond the containment site.

Information about the monitoring programs in place at active storage projects sites is shared through networks such as the IEA GHG monitoring network and CO2NET.

The IEA GHG has developed an online monitoring selection tool to identify and prioritise techniques that could form part of a monitoring program.

A Technical Basis for Carbon Dioxide Storage, prepared by members of the CO2 Capture Project, has a chapter devoted to various monitoring techniques and their limitations and applications. The chapter also includes several case studies.

In January 2009, the US Department of Energy published a comprehensive best practices module for monitoring geological storage projects. The report, Monitoring, Verification, and Accounting of CO2 stored in Deep Geologic Formations, includes a comprehensive list of monitoring techniques including a description of each, the benefits of using each technique and the challenges. It also categorises technologies into the monitoring domains.

Outline of steps in performance assessments

The following generalizes an approach for conducting performance assessments of a geological storage site:

1.Define the characteristics of the project and establish the assessment context.

Some of the issues that need to be considered within the assessment context are:

  • Environmental impact of the proposed sink mechanism;
  • CO2 capacity;
  • Retention/residence time of CO2 in the storage site;
  • Potential for accelerated leakage of CO2;
  • Rate of CO2 uptake by the storage site;
  • Validation of storage in the sink; suitability of the sink/match to the emission source and type; and
  • Cost of implementation/utilization of the sink mechanism.

2.Utilize online resources to identify and rank the important features, events and processes for the project.

  • Establish plausible scenarios for the long term evolution of the geological storage site;
  • Make use of qualitative assessment studies to appropriately rank the scenarios for subsequent performance assessment analyses. Qualitative studies can be used to identify where further, more detailed studies will be most beneficial and can assist in identify whether deterministic and/or probabilistic assessments should be adopted. The choice will depend on the nature of the questions which in turn determines the nature of the mathematical models used to describe the system; and
  • Conduct appropriate quantitative analyses on scenarios to confirm performance of the geological storage site will meet the criteria developed within the assessment context. If a performance criterion is not met, the design is reiterated until a satisfactory design is achieved or a new site must be found.

There are some important decisions that should be made before evolving the performance assessment towards risk evaluation. These questions relate primarily to the adequacy of the data, the methods used in the analyses, and the uncertainties associated with the analysis. Some of these decisions are listed below. While this list was not meant to be exhaustive it should provide the reader with a good overview of the types of questions to be asked at the end of any component of the performance assessment.

  • Is the performance (risks) much lower than initially estimated or is there no longer an issue of concern with stakeholders? If so, end the performance assessment here.
  • Have new issues developed? If so, return to establishing the context for the project.
  • Should new scenarios be considered? If so, return to identifying the risks.
  • Are the methods used in the analyses appropriate? If not, return and redo analyses using different methods.
  • Are the results of the analyses considered reasonable? If not, return and redo analyses using different methods.
  • Is the level of uncertainty associated with the estimates considered acceptable? If not, acquire better data and redo analyses using new data or better techniques.


Performance assessment evaluates the performance of an element of a storage project against one or more performance standards. It includes engineering and safety aspects of the initiative and is one aspect of the risk management process.

Risk management provides a comprehensive decision-making process that aids decision-makers in identifying, analyzing, evaluating and controlling all types of risks, including risks to health and safety.

A performance assessment should begin with defining the basic parameters for the study. This includes determining the key stakeholders and process to be followed, developing a performance assessment team and defining the scope for the study. The most crucial components to consider are selection of assessment criteria, description of the storage concept and describing the storage site. The most difficult component to undertake is selection of assessment criteria for the evaluation. This is the focus of much of the activity in current research and field demonstration in measurement, monitoring and verification.

Current practice for most geologic storage project is to use a systems analysis approach for determining and evaluating risks. This involves developing a list of features, events and processes and how they interact and will managed within the storage system. An online features, events and processes (FEPs) database has been developed to help with their identification. It includes FEPs that are relevant to long-term safety and performance of geological storage systems. Classification of FEPs occurs against the context for the performance assessment. This helps to determine which FEPs are important to consider. After FEP classification, scenarios are developed to identify, describe and select futures relevant to the performance assessment of the site. This provides the overall framework for the performance assessment and FEP selection. Base Scenarios (the expected evolution of the storage system) and Alternative Scenarios (those that illustrate the potential outcomes of uncertainties) are typically produced.

An analysis strategy is chosen to establish the likelihood of exceeding criteria established in the assessment context stage. Different analysis methods will be chosen based on accuracy needed in the results, cost, data available, level of team's expertise and the acceptability of the analysis method to stakeholders. The main tool for these analyses is numerical modeling of the conceptual physical/chemical models in different scenarios. This produces quantitative results which can be used for qualitative, semi-qualitative or quantitative analyses.

Measuring, monitoring and verification ensure that CO2 injection has been environmentally safe and sound. It also provides some of the necessary CO2 accounting required under emission trading scenarios such as the Kyoto Protocol. Monitoring the fate of CO2 involves monitoring migration, leakage and seepage and is carried out in the subsurface, near-surface and the atmosphere. Monitoring programs are developed for each distinct phase of a project – pre-operation, operation, closure and post-closure.


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U.S. EPA (Environmental Protection Agency). Class I underground injection control program: Study of the risks associated with Class I underground injection wells. U.S. Environmental Protection Agency report EPA 816-R-01-007, 2001.

Wildenborg, T., T. Leijnse, E.Kreft, M.Nepveu and A. Obdam. Long-Term Safety Assessment of CO2 Storage: The Scenario Approach. Proceedings 7th International Conference of Greenhouse Gas Technologies, GHGT-7, Paper I3-3, Vancouver, 5 p, 2004.


Quintessa's online generic FEP database for the geological storage of CO2:

EPA's National Risk Management Research Laboratory (NRMRL):

Society for Risk Analysis (SRA):

Crystal Ball:



TESLA decision making tool

Interactive Design of Monitoring Programmes for the Geological Storage of CO2

CO2 Capture Project: and

The US Department of Energy/National Energy Technology Laboratory guide to best practice for Monitoring and Verification:

IEA GHG Monitoring Network:

The Weyburn-Midale project:

The report from the first phase of the Weyburn-Midale CO2 monitoring and storage project:

A Technical basis for carbon dioxide storage. Publication available online from the CO2 Capture project once logged in as a user.: