Numerical assessment of the near-wellbore rock matrix permeability gain due to thermal stimulation

International audienc

Simulation of CO2 storage in coal seams: Coupling of TOUGH2 with the solver for mechanics CODE_ASTER®

A symposium on applications and enhancements to the TOUGH codes for multiphase fluid, heat, and chemical transport at the Lawrence Berkeley National Laboratory (LBNL)International audienceAmongst the various geological storage options currently under consideration, CO2 storage in coal formations presents the most economic potential for middle-term spreading but also the most uncertainties and technical difficulties. This study (part of the CARBOLAB project) investigates coupled flow and mechanical processes that will take place around the injection point at the bottom of the Montsacro mine in Asturias, Spain. In order to quantify the strain and stress fields due to changes in the fluid pressure field and to account for stress/sorption dependent porosity/permeability effects, an efficient coupling between TOUGH2/EOS7C, a special module with an Extended Langmuir Sorption model, and the solver for mechanics CODE_ASTER® has been developed by BRGM

Accounting for end-user preferences in earthquake early warning systems

Earthquake early warning systems (EEWSs) that rapidly trigger risk-reduction actions after a potentially-damaging earthquake is detected are an attractive tool to reduce seismic losses. One brake on their implementation in practice is the difficulty in setting the threshold required to trigger pre-defined actions: set the level too high and the action is not triggered before potentially-damaging shaking occurs and set the level too low and the action is triggered too readily. Balancing these conflicting requirements of an EEWS requires a consideration of the preferences of its potential end users. In this article a framework to define these preferences, as part of a participatory decision making procedure, is presented. An aspect of this framework is illustrated for a hypothetical toll bridge in a seismically-active region, where the bridge owners wish to balance the risk to people crossing the bridge with the loss of toll revenue and additional travel costs in case of bridge closure. Multi-attribute utility theory (MAUT) is used to constrain the trigger threshold for four owners with different preferences. We find that MAUT is an appealing and transparent way of aiding the potentially controversial decision of what level of risk to accept in EEW

Assessment of CO2 health risk in indoor air following a leakage reaching unsaturated zone: results from the first representative scale experiment

International audienceLeakage of CO2 from geological reservoirs is one of the most fearsome unexpected scenarios for CO2 storage activities. If a leakage reaches the ground level, exposure to high CO2 concentrations is more likely to occur in low ventilated spaces (pit dug in the ground, basement, building) where CO2 could accumulate to high concentrations. Significant literature and models about indoor exposure resulting from intrusion of soils gases in building are available in several domains (e.g., contaminated soils, radon, etc.). However, there is no guarantee that those approaches are appropriate for the assessment of consequences of CO2 leakage due the specificity of CO2 and due to the singularities of the source in case of leakage from anthropic reservoirs. Furthermore, another singularity compared to conventional approaches is that the risk due to CO2 exposure should be evaluated considering acute concentrations rather than long term exposure to low concentrations. Thus, a specific approach is needed to enable a quantitative assessment of the risk for health and living in indoor environment in case of leakage from a reservoir reaching the unsaturated zone below the buildings. We present the results of the IMPACT-CO2 project that aims at understanding the possible migration of CO2 to indoor environment and to develop an approach to evaluate the risks. The approach is based on modelling and experiments at laboratory scale and at field representative scale. The aim of the experiment is to capture the main phenomena that control the migration of CO2 through unsaturated zone, and its intrusion and accumulation in buildings. The experimental results will also enable numerical confrontation with tools used for risk assessment. Experiments at representative scale (Figure 1) are performed on the PISCO2 platform (Ponferrada, Spain) specifically instrumented and designed for understanding the impacts of CO2 migration towards the soil surface. The experiment is composed of a 2.2 m deep basin filled with sand upon which a specifically designed cylindrical device representing the indoor condition of a building (with controlled depressurization and ventilation) is set up. The device includes a calibrated interface that represents a cracked slab of a building. The injection of CO2 is performed at the bottom of the basin with a flow rate in the range of hundreds of g/d/m². The first results show that the presence of a building influences significantly the transport of CO2 in the surrounding soil leading to two competing phenomena: 1) seepage in the atmosphere mainly controlled by diffusion gradient and 2) advective/diffusive flux entering the building due to the depressurization. Models have been established to quantitatively assess the proportion of CO

Assessment of CO2 Health Risk in Indoor Air Following a Leakage from a Geological Storage: Results from the First Representative Scale Experiment

If a leakage of CO2 out of a geological reservoir were to happen and to reach the vadose zone below a building, CO2 could migrate through the vadose and the building's slab and accumulate in the building, leading to possible acute risk for the inhabitants. A representative-scale experiment, including a prototype for a building, was developed to better understand and quantify this possible risk. It brought fruitful directions for further modeling work, since unexplained CO2 peaks were observed in the prototype. Numerical simulations were carried out to address the variability of CO2 concentrations considering the influence of soil and building properties as well as meteorological conditions, with promising results for risk analysis

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

Anticipating abrupt shifts in temporal evolution of probability of eruption

International audienceEstimating the probability of eruption by jointly accounting for different sources of monitoring parameters over time is a key component for volcano risk management. In the present study, we are interested in the transition from a state of low-to-moderate probability value to a state of high probability value. By using the data of MESIMEX exercise at the Vesuvius volcano, we investigated the potential for time-varying indicators related to the correlation structure or to the variability of the probability time series for detecting in advance this critical transition. We found that changes in the power spectra and in the standard deviation estimated over a rolling time window both present an abrupt increase, which marks the approaching shift. Our numerical experiments revealed that the transition from an eruption probability of 10–15% to > 70% could be identified up to 1–3 h in advance. This additional lead time could be useful to place different key services (e.g., emergency services for vulnerable groups, commandeering additional transportation means, etc.) on a higher level of alert before the actual call for evacuation

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

Borehole damaging under thermo-mechanical loading in the RN-15/IDDP-2 deep well: towards validation of numerical modeling using logging images

International audienc

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