Determining performance indicators for linking monitoring results and risk assessment – application to the CO2 storage pilot of Hontomin, Spain

International audienceRisk management is an essential part of any CO2 injection and storage operation, not only to ensure there will be no detrimental impacts towards health or the environment, but also as a mean to build trust with stakeholders. Operational risk management can be divided in three parts: 1/ risk assessment, where risk is studied and commonly involves numerical modelling; 2/ monitoring during operations is needed in order to check that the evolution of the site is in line with the assessment; and 3/ risk mitigation or risk treatment which includes any measure that can lower the risk either before or during operations. Currently, there are few papers looking at the links between these three parts, which are nonetheless essential for an optimal management of the risks: monitoring systems and mitigation measures should be put in place according to the results of risk assessment; monitoring should have set thresholds for activating corrective measures; risk assessment should be updated with results from monitoring, etc. The focus of this work is on the feedback from monitoring towards risk assessment and risk mitigation. Many papers already studied the field of " history-matching " , but this is generally restricted to the update of the geological and dynamical models of the operation, and it deals less frequently with the risk assessment update. However, as some field experience demonstrated (most famously at Sleipner), there is a high probability that the CO2 plume behaves differently than initially foreseen. This can have a large effect on the assessment of risks: some risks might not be relevant anymore while new risks might be discovered. It is thus important to get a current understanding of the risks during operations, otherwise some decisions (for instance deploying contingency monitoring or activating mitigation measures) could be based on outdated information. In addition, it is important that predetermined thresholds are in place for activating the appropriate mitigation measures. By comparing the initial assessment with the site evolution, it is expected that some deviation will occur. We should then distinguish between:-" acceptable " deviations that would not necessitate an update of the risk assessment-" large " deviations that would lead to an update of the risk assessment-" unacceptable " deviations that would lead to an update of risk assessment and the activation of appropriate mitigation measures. The purpose of this work is to propose indicators that enable to quantify the deviations between the observations from the monitoring system and the predictions from the risk assessment (including numerical modelling). Criteria are then created for distinguishing acceptable, large and unacceptable deviations. This is applied on a real operation: the CO2 storage pilot site of Hontomin, in Spain, operated by CIUDEN. Setting the indicators consists in finding one or several metrics related to each of the monitoring technique currently deployed at the site. The metric should allow to link the observations to the risk assessment. For instance the pressure measurement at or near the injection well can be linked to the risk of wellbore leakage. The completeness of the indicators is ensured by checking that each identified risk is represented by at least one indicator. The main difficulty of this work is to propose indicators that are both operational (i.e. can be computed quickly and easily) and in coherency with the stated objective. For instance, for monitoring techniques that are imaging the plume, the issue is to create meaningful quantitative indicators (e.g. approximate area of the plume, maximum distance from the injection well, or probability of leakage in the caprock)

Management of uncertainties on parameters elicited by experts – Applications to sea-level rise and to CO 2 storage operations risk assessment

International audienceIn a context of high degree of uncertainty, when very few data are available, experts are commonly requested to provide their opinions on input parameters of risk assessment models. Not only might each expert express a certain degree of uncertainty on his/her own statements, but the set of information collected from the pool of experts introduces an additional level of uncertainty. It is indeed very unlikely that all experts agree on exactly the same data, especially regarding parameters needed for natural risk assessments. In some cases, their opinions may differ only slightly (e.g. the most plausible value for a parameter is similar for different experts, and they only disagree on the level of uncertainties that taint the said value) while on other cases they may express incompatible opinions for a same parameter. Dealing with these different kinds of uncertainties remains a challenge for assessing geological hazards or/and risks. Extra-probabilistic approaches (such as the Dempster-Shafer theory or the possibility theory) have shown to offer promising solutions for representing parameters on which the knowledge is limited. It is the case for instance when the available information prevents an expert from identifying a unique probability law to picture the total uncertainty. Moreover, such approaches are known to be particularly flexible when it comes to aggregating several and potentially conflicting opinions. We therefore propose to discuss the opportunity of applying these new theories for managing the uncertainties on parameters elicited by experts, by a comparison with the application of more classical probability approaches. The discussion is based on two different examples. The first example deals with the estimation of the injected CO 2 plume extent in a reservoir in the context of CO 2 geological storage. This estimation requires information on the effective porosity of the reservoir, which has been estimated by 14 different experts. The Dempster-Shafer theory has been used to represent and aggregate these pieces of information. The results of different aggregation rules as well as those of a classical probabilistic approach are compared with the purpose of highlighting the elements each of them could provide to the decision-maker (Manceau et al., 2016). The second example focuses on projections of future sea-level rise. Based on IPCC's constraints on the projection quantiles, and on the scientific community consensus level on the physical limits to future sea-level rise, a possibility distribution of the projections by 2100 under the RCP 8.5 scenario has been established. This possibility distribution has been confronted with a set of previously published probabilistic sea-level projections, with a focus on their ability to explore high ranges of sea-level rise (Le Cozannet et al., 2016). These two examples are complementary in the sense that they allow to address various aspects of the problem (e.g. representation of different types of information, conflict among experts, sources dependence). Moreover, we believe that the issues faced during these two experiences can be generalized to many risks/hazards assessment situations. References Manceau, JC., Loschetter, A., Rohmer, J., de Lary, L., Le Guénan, T., Hnottavange-Telleen, K. (2016). Dealing with uncertainty on parameters elicited from a pool of experts for CCS risk assessment. Congrès λµ 20 (St-Malo, France). Le Cozannet G., Manceau JC., Rohmer, J. (2016). Bounding probabilistic sea-level rise projections within the framework of the possibility theory. Accepted in Environmental Research Letters

Developing subsurface energy exploitation strategies by considering seismic risk

International audienceThe injection or extraction of fluids in the subsurface for energy purposes (e.g. geothermal exploitation, CO2 storage or geological energy storage) requires both the operation efficiency and the associated environmental risks to be assessed and controlled. Even though scientific and technological progress allows more accurate 3D modelling of the subsurface, we still do not have a thorough understanding of coupled underground hydromechanical processes. Indeed, the injection or production of fluids interacting with existing geological features can still result in unintended and unexpected 'harmful' consequences. This review aims to propose a unified strategy ranging from an understanding of the hydromechanical factors at the origin of the induced seismicity to seismic risk evaluation expressed in terms of ground-motion effects. The challenge is to utilize mechanical modelling to anticipate the evolution of seismicity; how the population perceives this is also an important factor to be taken into account in this risk evaluation. While mechanical modelling may include some degree of uncertainty, probabilistic analysis is capable of providing a quantitative estimation of the risk incurred and feedback to the exploitation strategy

Development of a risk assessment tool for deep geothermal projects: example of application in the Paris Basin and Upper Rhine graben

International audienceThis paper presents the development of a tool to perform risk assessment for deep geothermal projects. The tool is aimed at project developers to help them present their project to local authority, decision-makers and financers so they can highlight how they take into account risks and consider mitigation measures to minimize them. The main criteria for this tool are the simplicity of use, the quality of presentation and flexibility. It is based on results from the H2020 GEORISK project that identified risks that apply to geothermal projects and proposed insurance schemes all over Europe. A characteristic of this tool is that it considers all the categories of risks that a project may face, including geological, technical, environmental risks as well as risks related to the social, economic and political contexts. The tool can be customized: selection of risks in a list that can be completed, adaptable rating scheme for risk analysis, possibility to choose the best display for results depending on the user needs. Two case applications are presented, one in the Paris Basin considering a doublet targeting the Upper Trias, a geological layer that presents some technical challenges; and one in the Upper Rhine graben targeting a fault zone, where the risk of induced seismicity must be carefully considered. A posteriori risk assessment highlights the main issues with these types of projects, and the comparison between the two cases emphasizes the flexibility of the tool, as well as, the different ways to present the results depending on the objective of the analyses

Facilitating the deployment of CO2 storage by exploiting synergies with geothermal energy

International audienceGeological CO2 storage should play a crucial part in the net zero emissions by 2050 target, as suggested by recent reports from the IEA or the IPCC. It contributes first by decarbonising high-emission sector by storing CO2 emitted during energy and industrial production. It is also a key aspect for achieving technological CDR (Carbon Dioxide Removal). Methods such as BECCS (BioEnergy with Carbon Capture and Storage) and DACCS (Direct Air Capture with Carbon Storage) rely on geological storage. Yet, the deployment of full-scale storage projects to date has not reached an adequate pace of change in order to contribute significantly to reach the net zero objective. Many factors can explain this observation: difficulty of a reliable business case (economic barrier), lack of political support and awareness (political barrier), concerns over public opposition (societal barrier), knowledge of favourable subsurface conditions (geological barriers), etc. In some ways, CO2-EOR, which is a synergy between CO2 storage and hydrocarbon production, has played a role in helping the deployment of CO2 storage, by providing business case and demonstrating the viability for parts of the CCUS chain. However, CO2-EOR also often encounter negative appreciation for its direct connection to hydrocarbon production, and contribution to CO2 emissions. In this paper, we focus on the synergy between CO2 storage and geothermal energy. Several authors have proposed such synergies. Tillner et al. (2013) envisage the coexistence of CO2 injection and a geothermal doublet. Buscheck et al. (2016, 2017) propose to exploit the thermal (and physical) energy of brine produced when injecting CO2. Kervévan et al. (2017) propose to dissolve CO2 in the geothermal brine and to store the resulting fluid in saline aquifer by using a geothermal doublet. Pure CO2 has also been proposed as a geothermal working fluid instead of water, notably due to favourable thermodynamic properties. CO2 based geothermal systems encompass two concepts: i. CO2-EGS (Enhanced or Engineered Geothermal Systems) first proposed by Brown (2000); ii. CO2 Plume Geothermal (CPG) in hydrothermal reservoirs introduced by Randolph and Saar (2011). This study aims to propose a structured approach to evaluate to which extent a combination of CO2 storage and geothermal energy would facilitate the deployment of CO2 storage. It will compare the global performance of the various options for combining CO2 storage and geothermal energy with the expected performance of a conventional CO2 storage project in saline aquifer. The proposed approach is based on BRGM's new method for performance assessment of subsurface uses. The method defines "performance" as any required conditions that would contribute to meet the objectives of the project. For a CO2 storage project, performance is primarily measured in terms of the quantity of CO2 stored in the targeted reservoi

Methodologies and technologies for mitigation of undesired CO 2 migration in the subsurface

International audienceThe development and implementation of the CO2 Capture and Storage (CCS) technology is highly dependent on the assurance of the storage process safety with regards to a potential CO2 leakage from the target zone. Low permeability caprocks are viewed as critical element for a safe containment of CO2 in the target storage formation. As a result, the presence of any potential pathway is of a major concern since it may allow buoyant CO2 to migrate along and reach an overlying formation or be emitted at the surface, potentially impacting drinking water resources or sensitive stakes at the surface. Undesired CO2 migration may occur through man-made (abandoned and operational wells) and/or natural (caprock sealing defects including faults, fractures and high permeability areas) pathways. Managing a potential CO2 leakage risk scenario is of first importance and a dedicated, site-specific strategy has to be set up. The storage safety could be guaranteed through an adequate site selection and characterization leading to the choice of a site where the evolution of the CO2 plume and potential impacts of the storage are judged acceptable. Specifically to this given storage site, a proper risk-management process should be set up to anticipate the potential deviations from this acceptable behavior, including assessing the risks, monitoring the site to detect any potential loss of confinement, mitigating any potential leakage and remediating possible impacts.This study is focused on the risk treatment stage, more specifically on the methodologies and technologies for mitigation and remediation of unpredicted CO2 migration in the subsurface. To date this subject has not been addressed effectively although it is currently receiving more attention from the industrial and scientific communities. This evolution may be linked with the new regulations on CO2 geological storage, notably in Australia, Europe and in the USA, which specify requirements on mitigation and remediation methods.A comprehensive knowledge of mitigation techniques is needed to meet these requirements, which can be summarized with the three following categories:- Technical issue – the first challenge is to determine which ones of the existing technologies applied on the source, the transfer pathway or directly on the impacts may be adapted to avoid, reduce or correct any potential impacts induced by a CO2 migration. In other words, these are the scientifically conceivable measures;- Operational issue – from an operational perspective, the maturity of a technology is essential to ensure its feasibility. The achievability of one measure is dependent on additional criteria especially on the balance between the benefits (impact avoided) and the costs (economiccosts and potential environmental negative impacts of the measure). The second challenge is therefore to specify properly those criteria for the measures and to develop tools to assess the relevance of each conceivable measures;- Implementation issue – the third challenge is, based on the knowledge available at a given time, to produce an intervention plan as required by the above-cited regulations. This plan should answer to the identified risk events, and also prepare the operator and the competent authority to make an informed decision for choosing the best mitigation and/or remediation option at the time of the detection of an abnormal behavior in the CO2 storage complex.The technical issue has already been tackled and with several technical papers devoted to specific techniques aiming at reducing the potential risks and impacts of CO2 based on either existing work conducted in other fields (e.g. oil and gas industry, soil or water remediation) or specifically developed for CO2 storage. However, new categories of remediation techniques have recently appeared based on newly emerging technologies. In addition there is a need of comparative data to help operators to select the most adapted measure. Decision-making tools are also required to balance the benefits gained by the implementation of a mitigation measure and its economic costs and potential environmental impacts. Finally, there is a lack of integrated studies on the mitigation plan setting-up process. For instance, no comparison between the different intervention strategies of existing and future CO2 storage projects has been published. There is thus a need of gathering the best practices for mitigation of undesired CO2 migration based on the scientific literature and experience gained from various CO2 geological projects.In line with these statements, BRGM and IRIS conducted a literature and experience review on the methodologies and technologies for mitigation of undesired CO2 migration in the subsurface on behalf of the IEA Greenhouse Gas R&D Program.The state of knowledge of CO2 leakage mitigation and remediation technologies has been first presented from a technical point of view. Thus, for different scenarios, the potential actions for avoiding, reducing or correcting impacts caused by an unwanted CO2 migration have been reviewed. The choice of the appropriate measure strongly depends on the nature of the leak. The intervention on leakage through man-made pathways (well remediation) stems from the oil and gas industry experience, and for some of them are considered as standard operations. However, in some cases of man-made leakage pathways, and more importantly in most cases of natural ones, the operator may not be able to rely on the well engineering experience, and may rather rely on either fluid management techniques or new breakthrough technologies for modifying the leaking paths or fluid properties. In case of an impacting CO2 migration, measures may be applied to remediate environmental impacts.The state of knowledge presented in this study integrates both measures that are standard and technically feasible at the present time as well as innovative and under development ones. For each measure and when possible, a technical description of the intervention technique, generic cost and time elements (intervention delay, efficiency time duration) as well as a discussion on the maturity of the technique are provided. Decision-making tools (cost-benefit, cost-effectiveness and multi-criteria analyses) integrating those criteria to help choosing the optimal series of remediation actions are presented in this study. The third part of the work is a review of the existing plans and guidelines for designing such intervention plans. A qualitative survey has been performed among a list of CO2 and natural gas storage sites. Recommendations – research and development directions or best practices - are proposed according to the outcomes of the entire study