• Energy Research

AbstractThis 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.

Persistent scatterers synthetic aperture radar interferometry (PSI) analysis is viewed as a promising monitoring technique for multiyear detection of ground surface displacements during long term CO2 injection into deep aquifers (of the order of 25 to 50 years). This technique was successfully implemented at the CO2 storage site of In-Salah (Algeria). Yet, this success may not be generalized to future onshore industrial-scale CO2 storage sites, which are planned in far more complex contexts mostly presenting natural terrains variationeither agricultural or vegetal areas. These areas arecharacterized by poor Persistent Scatterer (PS)density, which might locally drop to zero, hence hampering the deployment of the PSI technique. For illustration purpose, a sector in the Paris basin (of 3,455 km²), where the potential implementation of CO2 storage sites has been investigated, is characterized by a land use composed of less than 5 % of artificial or urban areas and more than 95 % of natural (mainly forests) and agricultural areas. In such natural terrains, the absence of bright man-made structures might lead to sparse PS network (with density ~10 PS/km² to less than 1PS/km²). This constitutes a major obstacle to the phase unwrapping stage, for which the solutions are directly dependent on the PS density and makes reliable estimation of deformation using PS techniques a challenging task. The present study aims at exploring the applicability of two approaches to enhance the performance of the PSI technique in such constraining conditions for long term monitoring of CO2 storage sites. The first approach relies on the implementation of network of corner reflectors (CR) corresponding to artificial devices installed on ground to complement the existing "natural" PS network. A strategy for optimization (number and position) the CR network is proposed based on the position of the existing PS and on hydro-mechanical large-scale simulations constrained by the observations (through history-matching). The second approach relies on the use of two advanced PSI processing techniques: 1. Diffuse scatterers analysis (based on Ferretti et al., 2011), which can improve considerably the density of usable "natural" scatterers on certain un-urbanised area; 2. MulSAR technique (Pinel-Puyssegur et al., 2012), which is a processing method, that produces denoised wrapped phase time series, i.e. which facilitates the retrieval of the deformation signal obscured by decorrelation noise. To test the efficiency of these approaches, a synthetic case was constructed as follows: 1. we use as a "reference case" the deformation field observed at In-Salah during CO2 injection into the KB-501 well between 2004 and 2009; 2. the surface characteristics of this reference case are then modified by "artificially" applying the surface conditions (urbanized areas, natural terrains, either agricultural or vegetal areas) of an on-shore site in Western France, which can be considered representative of future industrial-scale storage sites in Europe. 3. by comparing the deformation field retrieved by the PSI technique combined with the afore-described approaches with the one of the reference case, the level of improvement can be estimated. Results show that the direct application of advanced processing techniques may be limited for zones with very high density of natural terrains (>90 % of the surface area), but can still be efficient for zones with moderate-to-high density of natural terrains. On this basis, we propose to improve PSI analysis in highly vegetal / agricultural areas for long term CO2 storage monitoring based on a combination of advanced processing PSI methods and an optimized CR network. References Ferretti, A., Fumagalli, A., Novali, F., Prati, C., Rocca, F., Rucci, A., 2011. A New Algorithm for Processing Interferometric Data-Stacks: SqueeSAR . IEEE Transactions on Geoscience and Remote Sensing 49 (9), 3460-3470. Pinel-Puyssegur, B., Michel, R., Avouac, J-P., 2012. Multi-link InSAR time series: enhancement of a wrapped interferometric database. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 5(3), 784-794.

Abstract Geological storage of the greenhouse gas CO 2 has the potential to be a widespread and effective option to mitigate climate change. As any industrial activity, CO 2 storage may lead to adverse impact on human health and the environment in the case of unexpected leakage from the reservoir. These potential impacts should be considered in a risk assessment process. We present an approach to assess the impacts on human health in case of CO 2 leakage emerging in the unsaturated zone under a building. We first focus on the migration of the CO 2 in the unsaturated zone and the foundation through numerical simulation with sensitivity analysis. Our results show that the intrusion of CO 2 into a building is substantially attenuated by the unsaturated zone and the foundation and may lead only under very specific conditions (very low ventilated parts of buildings, high flow rate and/or building situated very close to a leaking pathway) to hazardous CO 2 indoor concentrations. We have then integrated the former results in a global toolbox that provides an efficient and easy-to-use tool for decision support, which enables to assess the impacts on human health of CO 2 leakage from the reservoir to a building.

To guarantee the safety of CO2 storage operations, to meet regulatory requirements and thus to be accepted by the public, the operator of a CO2 storage site has to demonstrate that the risks are adequately managed, which includes the treatment of potential irregularities. This paper proposes a methodology to choose a corrective measure and to optimize its sizing in case of leakage from a CO2 geological storage through a semi-pervious caprock, a fault, a fractured zone or any other leakage pathway on which it is difficult to directly act. The corrective measures considered in our work are limited to fluid and pressure management practices implemented for controlling the plume migration and eventually for extracting the leaking fluid. The methodology is based on the use of the Multi-Attribute Utility Theory (MAUT) which enables multi-criteria analysis over a continuous set of alternatives. The implementation on a case study illustrates the methodology applicability. The influence of the main assumptions and uncertainties are addressed through a sensitivity analysis.

This paper presents a method created for assessing the performance of concepts hybridizing geothermal energy and carbon capture and storage. The performance of a system can be represented by a set of key performance indicators. Those need to cover at least the quantity of energy produced, the amount of carbon stored, the environemental risk and impacts, the economics, and the uncertainties and challenges associated. The paper details the set of 17 indicators proposed for this study.We assessed these indicators for each of the 15 hybrid concepts that were found in the literature, through about 150 relevant papers. This shows that the concept that have a higher score in term of climate change mitigation potential have also a higher technical complexity. On the other hand, lower capacity concepts rely on more mature technology. This means they can scale faster and thus make a more substantial contribution.

CO2 capture and storage (CCS) is recognized as a promising solution to tackle greenhouse gas emissions. Key issues associated with CCS relate to the integrity of the reservoir and the containment effectiveness. Some risk events (e.g. regional over-pressurization, leakage through a fault or an abandoned well) identified in the risk analysis may be linked with surface deformations anomalies, which can be detected and followed using surface deformation measurements.At In-Salah (Algeria), Interferometric Synthetic Aperture Radar (InSAR) data are available for all points due to ideal surface conditions. If a similar injection occurred in constrained conditions (large cover of vegetated areas for instance), a geodetic network (set of corner reflectors that constitute artificial measurements points) could be used to compensate the scarcity of existing persistent scatterers. The present study aims at exploring the feasibility of using such a geodetic network as part of the monitoring plan in constrained conditions. The sizing of such a network is discussed regarding three monitoring objectives: regional-scale surveillance, local anomaly with known and unknown spatial locations. In the context of In-Salah, a very limited number of measurement points (∼20) enables capturing the regional deformation pattern. The addition of a series of less than 5 supplementary points brings useful information to detect local anomalies of small-to-moderate (e.g. subsidence, with 1 km radius and 2 mm/y maximal amplitude) size for a known position. For detecting an unpredicted anomaly, the measurements network density needs to be largely increased, making the method more expensive. Though the results are not directly transposable in other settings, this experience feedback brings useful orders of magnitude and an original risk-oriented approach.