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For integrating green hydrogen to the future energy system, underground storage facilities are needed. So far, there is no underground hydrogen pore storage facility in Germany. However, there is a lot of experience in town gas, natural gas , and CO2 underground storage which now can be used for hydrogen storage pre-feasibility assessments, explorations and operations.In this approach the Ketzin anticline (Germany) is used for a pre-feasibility assessment for hydrogen underground storage in a saline aquifer by using experimental and measurement data from its time as a CO2 test site during 2004 to 2017.For this first feasibility assessment we focused on the influence of several reservoir parameters on hydrogen solubility and the production rate. Therefore, the influence of the brine´s salinity, capillary pressure, reservoir pressure and temperature of two potential storage formations at Ketzin site is analyzed.The Stuttgart formation was already used as a CO2 storage formation during the projects CO2SINK, CO2MAN, COMPLETE. Due to loss reduction by a optimal structural trapping the potential hydrogen injection and production well is located at the top of the anticline – about 1.5 km north to the former CO2 storage test site. Based on Fleury´s experimental data from 2013, including capillary pressure, six parameter setups are created to simulate six hydrogen production and injection cycles.For the second storage formation, the Exter formation, less experimental and measurement data is available. Therefore, six scenarios were designed on the basis of literature values. The end members represent a low and a high hydrogen recovery scenario which combine the best and worsed possible parameter setup for this formation.The results show that it is important to consider the regional conditions individually and to respond to the specifications of the site to minimize economic and safety risks in hydrogen underground storage.

Seismic and geoelectric methods are used as complementary tools for the identification of fluid/gas effects in underground storage and production scenarios. Both methods present a different resolution. Seismic data tend to be acquired by much more dense geometrical layouts, and geoelectric acquisition as a potential field method shows information integrated over spatial distances. We present results matching seismic and electrical resistivity tomography (ERT) results from two repeat surveys performed during CO 2 storage operations at the Ketzin pilot site in Germany. The approach is based on data acquired in 2009 and 2012 at different stages of total injected CO 2 volume. Masses are obtained from the averaged change in acoustic impedance and are compared to masses inferred from inverted electrical resistivities. Archie's equation is used to obtain saturations from the ERT models. The sensitivity of the background resistivity, R 0 , as a relevant parameter in determining the mass of injected CO 2 is analysed. A specific threshold analysis based on seismic thickness by bin has been applied to investigate the matching of seismically and ERT obtained masses. Both mass estimates match comparatively well, but show inherent sensitive parameters and their corresponding impact as temporal and spatial uncertainties that may cause mass differences for the areas of investigation.

Seismic and geoelectric/electro-magnetic methods are used as complementary tools for the identification of fluid/gas effects in underground storage and production scenarios. Both methods generally have very different resolution. Seismic tends to be acquired by much more dense geometrical layouts and the geoelectric or electro-magnetic acquisition being a potential field method shows information integrated over spatial distances. These inherent scale and design dependent differences require spatial tuning in joint inversion approaches and careful matching in independent interpretations of both methods. We present results matching seismic and electrical resistivity tomography (ERT) results from two repeat surveys acquired during CO2 storage operations at the Ketzin pilot site in Germany. The approach is based on data acquired in 2009 and 2012, at different stages of total injected CO2 volume. Volumes of injected mass are obtained from the averaged acoustic impedance change (seismic) in the vicinity of the injection well and compared to volumes inferred from the ERT cross-well acquisition. The results are compared radially with increasing distances from the injection location. Seismically derived masses of injected CO2 are used as a benchmark for a threshold-driven workflow analyzing the electric resistivity model. The cross-well ERT results have been obtained in a quadrant of the seismic survey acquisitions. Assuming radial symmetry for the ERT makes it possible to compare individual mass balances in the near-vicinity of the injection well. Archie's equation is used to obtain saturations from the tomographic geoelectric models. The sensitivities of parameters relevant in determining the mass of injected CO2 is analyzed. Variations in saturation exponent n, baseline resistivity R0, and porosity Φ enable specifying applicable ranges of the parameters and determining the investigation radii compared to the seismic derived benchmark. This is done for individual threshold levels for saturations derived from the ERT field data. Seismically and ERT obtained masses match comparatively well and subtle variations of the sensitive parameters are capable in explaining differences for individual investigation volumes. Applicable investigation radii lie between 20-100 m. A 10% in- or decrease of the mean parameters is able to match the seismic derived mass in this range. Above a threshold of 10% for the saturations, the derived mass decreases more rapidly showing a larger deviation from the seismic derived mass. Both methods underestimate the total injected mass. This is not surprising as there are both fluid related processes and structural heterogeneities not accounted for in either. Results of surface-downhole measurements support the findings and show applicability of the developed approach. The threshold-based approach may support the monitoring concept of a CO2 storage site and provides a basis for quantitative evaluation of its containment, as investigated in the frame of the EU project SECURe.

Designing low-cost network layouts is an essential step in planning linked infrastructure. For the case of capacitated trees, such as oil or gas pipeline networks, the cost is usually a function of both pipeline diameter (i.e. ability to carry flow or transferred capacity) and pipeline length. Even for the case of incompressible, steady flow, minimizing cost becomes particularly difficult as network topology itself dictates local flow material balances, rendering the optimization space non-linear. The combinatorial nature of potential trees requires the use of graph optimization heuristics to achieve good solutions in reasonable time. In this work we perform a comparison of known literature network optimization heuristics and metaheuristics for finding minimum-cost capacitated trees without Steiner nodes, and propose novel algorithms, including a metaheuristic based on transferring edges of high valency nodes. Our metaheuristic achieves performance above similar algorithms studied, especially for larger graphs, usually producing a significantly higher proportion of optimal solutions, while remaining in line with time-complexity of algorithms found in the literature. Data points for graph node positions and capacities are first randomly generated, and secondly obtained from the German emissions trading CO2 source registry. As political will for applications and storage for hard-to-abate industry CO2 emissions is growing, efficient network design methods become relevant for new large-scale CO2 pipeline networks.

We present the results of a rock physics driven workflow to analyze and steer a planned CO2 migration campaign, it combines a rock-physical seismic model, reservoir model and Bayesian scenario framework to assess monitoring configurations. The injection of CO2 into the subsurface requires a detailed understanding of the petrophysical properties and rock physical frame of the formation under stress. The underlying assumptions made for the unconsolidated high porosity formation have a significant impact on the expected seismic response. For a shallow aquifer pressure and saturation dependent elastic parameters are derived within a rock physical description. Distinguishing pressure and saturation related changes of the acoustic impedance is subject to the sensitivities of the properties used to derive the underlying seismic P- and S-velocities as well as densities. These uncertainties can induce a non-negligible variability in the footprint of a seismic image of the CO2 plume. The rock physics model is based on a solid frame consisting of quartz and clay and saturated with water and gas. The integrated workflow coupled with dynamic simulations provides a possibility to define and evaluate conformance measures during operation. Within this context the workflow is applied to the extended Svelvik CO2 field laboratory, which can be considered as a big sandbox model with capabilities for up-scaling to larger storage formations. An experimental design assessing the sensitivity of the information present for the site is translated into a scenario-based ensemble of dynamic models. Following, a practical quantitative workflow for a-priori assessment of monitoring strategies in probabilistic conformance verification is demonstrated. The results provide insight into the impact of different aspects of geophysical monitoring configurations (e.g., sparsity, noise levels, detection thresholds and timing) on the conformance verification accuracy.

The three-year (2017-2020) Pre-ACT project was established as one of the three large projects in the first round of the Accelerating CCS Technologies (ACT) program (https://act-ccs.eu). Pre-ACT was a collaborative effort between partners from six research institutes and four companies with an active role in CCS. The project ambition was to deliver cutting-edge research into the safe storage and monitoring of CO2, particularly to improve strategies for monitoring and management of the pore pressure distribution within the storage reservoir. Pre-ACT has established methodologies for assessing the conformance of a storage site, relative to its expected performance. The primary outputs are quantitative conformance systems (protocols), which rely on cost-effective monitoring, and guidelines on how to act in case of non-conformance. The protocols are applicable to industrial operators and focus on the main storage-related challenges for accelerated deployment of CCS: capacity, confidence and cost. We report here on the lessons learned within the project, both in terms of European collaboration between research institutes and industry partners in the new ACT-program, but most of all in terms of the new knowledge and methods related to monitoring and control over large-scale storage projects in the North Sea. In addition, we describe a unique experimental campaign with brine and CO2 injection at the new ECCSEL Svelvik CO2 Field Lab and touch upon the important work of communicating research findings to external stakeholders such as policy makers, regulators, and potential future CCS project operators.

Cheap and efficient groundwater pressure monitoring is a standard task in subsurface hydrology. We present application experience from a tube based pressure monitoring system that is applied to the Svelvik field laboratory for CO2 storage, Norway. In total 13 monitoring points were installed in depths between 51 and 89 m below ground level.The pressure sensor is located above ground. It is temperature compensated to reduce measurement errors due to temperature variations. The pressure sensor is connected to a downhole low diameter tube that has a perforation in the respective measurement depth. The tubes are installed as smart casing installations, i.e. in the borehole annulus. This allows to keep the borehole open during installation of other monitoring devices.Clean pumping of the well was not possible. Some filters were protected with fleece, while others were just perforated tubes. During installation, all tubes had hydraulic contact to the groundwater. After settling of the mud 3 of 4 fleece protected filters show sufficient communication, while all 9 filters that were just perforated were clogged and not usable for pressure monitoring.The system has following advantages: (i) the downhole material is robust and cheap, allowing for multiple measurement points; (ii) has a small diameter (6 mm in the present case); (iii) since the static pressure is removed, a smaller sensor range is required; (iv) the sensors are located at the top of the borehole and can be retrieved after the campaign. Further, it can be installed without downhole metal parts.The system has two disadvantages by design compared to submerged pressure sensors. (i) The absolute pressure can only be approximately determined, limited by the accuracy of the fluid density inside the tube. (ii) Pressure decreases can only be measured up to about 1 bar below piezometric head when the tube is filled with water.The upper metres, that may be exposed to temperatures below 0 °C are filled with antifreeze. The choice of antifreeze allows for a certain static pressure correction. Minimum weight liquid is pure ethanol with a density of about 0.8 kg, allowing to measure pressure up to 2.8 bars below piezometric head for e.g. the 89 m deep measurement.AcknowledgementsThis work has been produced with support from the SINTEF-coordinated Pre-ACT project (Project No. 271497) funded by RCN (Norway), Gassnova (Norway), BEIS (UK), RVO (Netherlands), and BMWi (Ger-many) and co-funded by the European Commission under the Horizon 2020 programme, ACT Grant Agreement No 691712. We also acknowledge the industry partners for their contributions: Total, Equinor, Shell, TAQA. We thank the SINTEF-owned Svelvik CO2 Field Lab (funded by ECCSEL through RCN, with additional support from Pre-ACT and SINTEF) for assistance during installation and for financial support.

Carbon Capture and Storage technology is considered to be able to contribute to a carbon neutral society and is again receiving increased attention in the efforts to reduce CO2 emissions. To ensure safe operation of such CO2 storage projects, reliable monitoring technologies are required. Due to the generally high electrical resistivity contrast between CO2 and formation water, Electrical Resistivity Tomography (ERT) can be considered one of the most effective geophysical techniques in the monitoring of CO2 migration in the subsurface.Within the ERA-NET co-funded ACT project Pre-ACT (Pressure control and conformance management for safe and efficient CO2 storage - Accelerating CCS Technologies) a CO2 injection and monitoring experiment was planned at the Svelvik CO2 Field Lab, located on the Svelvik ridge at the outlet of the Drammensfjord in Norway. The Svelvik field lab consists of four 100 m deep monitoring wells, drilled in July 2019, surrounding an existing well used for brine and CO2 injection. Each monitoring well is equipped with modern sensing systems including five types of fiber-optic cables, conventional and capillary pressure monitoring systems, as well as 16 ERT electrodes with a spacing of five meters.With 64 installed electrodes, a large number of measurement configurations is possible. We combine the free and open-source geophysical modeling library pyGIMLI with ECLIPSE reservoir modeling to simulate the expected behavior of all cross-well electrode configurations during a CO2 injection experiment. Simulated CO2 saturations are converted to changes in apparent resistivity using Archie's law. Different considerations have to be made to select a suitable set of electrode configurations, i.e. not too large geometric factors, maximum response to the predicted change, as well as sensitivity in the target area. We select sets of configurations based on different criteria, i.e. the ratio between the measured change in resistivity in relation to the geometric factor, the maximum change in apparent resistivity, and maximum sensitivity in the target area. The individually selected measurement schedules are tested by inverting them with different assumed data errors. The numerical results show adequate resolution of the CO2 plume.The CO2 injection took place between 27th October 2019 and 5th November 2019. Approximately two metric tonnes of CO2 were injected in 65 m depth. Preliminary field results indicate a considerably lower response than predicted by our model. These discrepancies can potentially be explained by oversimplified simulations as well as operational uncertainties. Results from baseline and repeat surveys can therefore support an integrated approach towards a revised static and dynamic model for the test site.Acknowledgements:This work was produced within the SINTEF-coordinated Pre-ACT project (Project No. 271497) funded by RCN (Norway), Gassnova (Norway), BEIS (UK), RVO (Netherlands), and BMWi (Germany) and co-funded by the European Commission under the Horizon 2020 programme, ACT Grant Agreement No 691712. We also acknowledge industry partners Total, Equinor, Shell, TAQA.Finally, we thank the SINTEF-owned Svelvik CO2 Field Lab (funded by ECCSEL through RCN, with additional support from Pre-ACT and SINTEF) for assistance during installations and for financial support.

Resolution within seismic imaging must be understood in all three dimensions to make quantitative approximations of subsurface geometries. Constructive interference of incident spherical waves within the first Fresnel zone will limit the resolution due to spatial aliasing. Motivated by the problem of estimating the influence of this effect on the volume uncertainty several interpretations of trapping faults, being equally probable within the first Fresnel zone, are perturbed and multiple realizations of a structural model constructed. After estimating the depth dependent mean frequency and velocity within a zone around the fault plane, the fault interpretations are stochastically perturbed. The frequency- and velocity-dependent perturbations of the dips are analytically derived based on geometric considerations. The anticipated maxima of the repositioned fault dips specify thresholds for deterministic definitions of high and low cases for the fault geometries in a framework. The structural models, resulting from repositioning the faults, show significant alterations of the hanging-wall and footwall horizon terminations due to the varying dips and repositioning of the interpretation. We have applied our to the structural and stratigraphic interpretation obtained for a prospect in the Gulf of Mexico. The spatial variations of the bounding faults result in a spread of volumetric outcomes when analyzing the gross rock volume of the compartment.

General solutions of inverse problems often can be obtained by introducing probability distributions to sample the model space. We have developed a simple approach to define an a priori space in a tomographic study and retrieve the velocity/depth posterior distribution by a Monte Carlo method. Utilizing a fitting routine designed for very low statistics to set up and analyze the obtained tomography results, we can statistically separate the velocity/depth model space derived from inverting seismic refraction data. A profile acquired in the Lesser Antilles subduction zone reveals the effectiveness of this approach. Resolution analysis of the structural heterogeneity includes a divergence analysis that can dissect long, wide-angle profiles for deep crust and upper mantle studies. The complete information of any parameterized physical system is contained in the a posteriori distribution. Methods for analyzing and displaying key properties of the a posteriori distributions of highly nonlinear inverse problems are therefore essential in the scope of any interpretation. It is possible to map velocity variations in their extent and structure by measuring the total as well as relative divergence of the velocity structure in the a posteriori space. We have applied the divergence analysis to a part of the transect where a backstop structure has been identified, and the method resolves shallow features and returns information concerning the confidence level of results. Assuming a relationship between forearc and backstop, we can obtain a structural image in accordance with previous interpretations. ©2010 Society of Exploration Geophysicists

It is commonly accepted that quasar redshifts have a cosmological character and that most of the quasars are at Gigaparsec distances. However, there are some cases where several quasars with completely different redshifts and a nearby active galaxy are aligned in a certain way or occupy a very small patch on the sky, which is claimed by some authors to be unlikely to happen by chance. Is there a small subset of quasars with non-cosmological redshifts? For quasars apparently associated with galaxies, we consider two scenarios for the origin of their redshift: 1. a standard, cosmological scenario, 2. a velocity-induced Doppler shift of a nearby object's spectrum (local, ejection scenario). We argue for a simple astrometric test which can distinguish between these two sources of quasar redshifts by constraining their proper motions. We give the predictions for the maximum possible proper motions of a quasar for the cosmological and local scenarios of the origin of their redshifts. We apply these theoretical results to the Bukhmastova (2001) catalog, which contains more than 8000 close QSO-galaxy associations. In the standard interpretation of quasar redshifts, their typical proper motions are a fraction of micro arc-second, and beyond the reach of planned astrometric missions like GAIA and SIM. On the other hand, the quasars ejected from local AGNs at velocities close to the speed of light would have proper motions 5-6 orders of magnitude larger, which would easily be measurable with future astrometric missions. The distributions of proper motions for the cosmological and local scenarios are very well separated. Moreover, the division corresponds nicely to the expected accuracy from GAIA and SIM., results unchanged, minor additions, 10 pages, 6 figures, 1 table, accepted to MNRAS

International audience; In 2007 the Sismantilles II experiment was conducted to constrain structure and seismicity in the central Lesser Antilles subduction zone. The seismic refraction data recorded by a network of 27 OBSs over an area of 65 km × 95 km provide new insights on the crustal structure of the forearc offshore Martinique and Dominica islands. The tomographic inversion of first arrival travel times provides a 3D P-wave velocity model down to 15 km. Basement velocity gradients depict that the forearc is made up of two distinct units: A high velocity gradient domain named the inner forearc in comparison to a lower velocity gradient domain located further trenchward named the outer forearc. Whereas the inner forearc appears as a rigid block uplifted and possibly tilted as a whole to the south, short wavelength deformations of the outer forearc basement are observed, beneath a 3 to 6 km thick sedimentary pile, in relation with the subduction of the Tiburon Ridge and associated seafloor reliefs. North, offshore Dominica Island, the outer forearc is 70 km wide. It extends as far as 180 km to the east of the volcanic front where it acts as a backstop on which the accretionary wedge developed. Its width decreases strongly to the south to terminate offshore Martinique where the inner forearc acts as the backstop. The inner forearc is likely the extension at depth of the Mesozoic magmatic crust outcropping to the north in La Désirade Island and along the scarp of the Karukera Spur. The outer forearc could be either the eastern prolongation of the inner forearc, but the crust was thinned and fractured during the past tectonic history of the area or by recent subduction processes, or an oceanic terrane more recently accreted to the island arc.

We propose a hybrid and adaptive smoothing method which accounts for attenuation and texture variations inherent in seismic data. Seismic conditioning is a fundamental step in numerous attribute assisted interpretation workflows. Despite its simplicity smoothing is utilized widely when it comes to noise reduction while preserving edges. Attenuation and dispersion of the acoustic wavefield often confines the use of such techniques to a limited texture or interval. We present a spatio-temporal windowing technique with adaptive smoothing. Depth dependant operator sizes are used to derive a variance based neighborhood estimate. This consecutively is used to condition the operator size in addition to defining the smoothing method. We alternate between the mean and median smoothing methods depending on the coherency in the seismic response. The median smoothing method is applicable to regions of high variability, whereas the mean form gives an enhanced continuity of the bedding and is hence preferable in coherent regions. The method proposed in this study is applied to a heavily faulted dataset offshore Norway on the continental shelf. Results obtained indicate that the method proposed for hybrid adaptive filtering can provide increased clarity in the identification and evaluation of subsurface features.

The 300-km-long north-central segment of the Lesser Antilles subduction zone, including Martinique and Guadeloupe islands has been the target of a specific approach to the seismic structure and activity by a cluster of active and passive offshore–onshore seismic experiments. The top of the subducting plate can be followed under the wide accretionary wedge by multichannel reflection seismics. This reveals the hidden updip limit of the contact of the upper plate crustal backstop onto the slab. Two OBS refraction seismic profiles from the volcanic arc throughout the forearc domain constrain a 26-km-large crustal thickness all along. In the common assumption that the upper plate Moho contact on the slab is a proxy of its downdip limit these new observations imply a three times larger width of the potential interplate seismogenic zone under the marine domain of the Caribbean plate with respect to a regular intra-oceanic subduction zone. Towards larger depth under the mantle corner, the top of the slab imaged from the conversions of teleseismic body-waves and the locations of earthquakes appears with kinks which increase the dip to 10–20° under the forearc domain, and then to 60° from 70 km depth. At 145 km depth under the volcanic arc just north of Martinique, the 2007 M 7.4 earthquake, largest for half a century in the region, allows to document a deep slab deformation consistent with segmentation into slab panels. In relation with this occurrence, an increased seismic activity over the whole depth range provides a new focussed image thanks to the OBS and land deployments. A double-planed dipping slab seismicity is thus now resolved, as originally discovered in Tohoku (NE Japan) and since in other subduction zones. Two other types of seismic activity uniquely observed in Tohoku, are now resolved here: “supraslab” earthquakes with normal-faulting focal mechanisms reliably located in the mantle corner and “deep flat-thrust” earthquakes at 45 km depth on the interplate fault under the Caribbean plate forearc mantle. None such types of seismicity should occur under the paradigm of a regular peridotitic mantle of the upper plate which is expected to be serpentinized by the fluids provided from the dehydrating slab beneath. This process is commonly considered as limiting the downward extent of the interplate coupling. Interpretations are not readily available either for the large crustal thickness of this shallow water marine upper plate, except when remarking its likeness to oceanic plateaus formed above hotspots. The Caribbean Oceanic Plateau of the upper plate has been formed earlier by the material advection from a mantle plume. It could then be underlain by a correspondingly modified, heterogeneous mantle, which may include pyroxenitic material among peridotites. Such heterogeneity in the mantle corner of the present subduction zone may account for the notable peculiarities in seismic structure and activity and impose regions of stick-slip behavior on the interplate among stable-gliding areas., This work has been funded by the European Union FP6 NEST (New and Emerging Science and Technology) — INSIGHT programme, under project “THALES WAS RIGHT” no. 029080, by French National Research Agency (ANR) CATTELL programme, German National Science Foundation DFG and TMR of IFM-GEOMAR as well as INSU-CNRS (missions embarquants), and by CPER Martinique for OBSISMER.

Summary Seismic attributes are one quantitative measure inherent in the phase, frequency and amplitude content of reflection and refraction data. Detection of structural and stratigraphic information based on seismic attributes is one of the fundamental workflows when it comes to interpreting subsurface features and seeking reservoir engineering information from seismic data. Not only do we need to identify the correct location of structures and edges like faults, it is of critical importance to understand throw profile behavior along faults and the true location of fault tips for volumetric and spill point analysis. Proper attribute analysis gives an interpreter a tool to help characterize the static and dynamic subsurface characteristics such as lithology terminations, possible juxtapositioning of lithologies and cross fault sealing capabilities to fluid flow. As we move into more complex environments, attributes based on structurally oriented filtering have been used to improve S/N ratios while preserving the discontinuities found in the data thereby enhancing stratigraphic boundaries and lithology terminations. We present an Euler-based method for directional filtering and apply this method to different structurally complex environments. We obtain improved S/N ratios and a more consistent and continuous edge mapping in comparison to conventional isotropic methods. Results for delineating salt in the Gulf of Mexico (GOM) and detecting fault extents offshore Norway indicate that methods based on structurally oriented filtering can provide increased clarity in the identification and evaluation of subsurface features.