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Summary The modular seismic acquisition system at the GFZ is basically suitable for underground exploration in crystalline, salt and clay rocks. Special features of the application result from the different properties of the media such as degree of heterogeneity, damping, anisotropy and their interaction with the excavation zone (EDZ) induced by the cavity (drifts, tunnels). This manifests itself in different frequency damping behaviour for compressional, shear and surface waves, which require a specific use of impulse and vibration sources at the joint depending on the task. Seismic borehole measurements can contribute to a significant improvement of the resolution.

The injection of CO2 at the Ketzin pilot CO2 storage site started in June 2008 and ended in August 2013. During the 62 months of injection, a total amount of about 67 kt of CO2 was injected into a saline aquifer. A third repeat 3D seismic survey, serving as the first post-injection survey was acquired in 2015, aiming to investigate the recent movement of the injected CO2. Consistent with the previous two time-lapse surveys, a predominantly WNW migration of the gaseous CO2 plume in the up-dip direction within the reservoir is inferred in this first post-injection survey. No systematic anomalies are detected through the reservoir overburden. The extent of the CO2 plume west of the injection site is almost identical to that found in the 2012 second repeat survey (after injection of 61 kt), however there is a significant decrease in its size east of the injection site. Assessment of the CO2 plume distribution suggests that the decrease in the size of the anomaly may be due to multiple factors, such as limited vertical resolution, CO2 dissolution and CO2 migration into thin layers, in addition to the effects of ambient noise. 4D seismic modelling based on dynamic flow simulations indicates that a dynamic balance between the newly injected CO2 after the second repeat survey and the CO2 migrating into thin layer and being dissolved was reached by the time of the first post-injection survey. Considering the considerable uncertainties in CO2 mass estimation, both patchy and non-patchy saturation models for the Ketzin site were taken into consideration.

The Ketzin pilot site for CO 2 storage in Germany has been operated from 2007 to 2013 with about 67 kt of CO 2 injected into the Upper Triassic Stuttgart Formation. Main objectives of this undertaking were assessing general feasibility of CO 2 storage in saline aquifers as well as testing and integrating efficient monitoring and long-term prediction strategies. The present study aims at revising the latest static geological reservoir model of the Stuttgart Formation by applying an integrated inverse modelling approach. Observation data considered for this purpose include bottomhole pressures recorded during hydraulic testing and almost five years of CO 2 injection as well as gaseous CO 2 contours derived from 3D seismic repeat surveys carried out in 2009 and 2012. Inverse modelling results show a remarkably good agreement with the hydraulic testing and CO 2 injection bottomhole pressures (R 2 = 0.972), while spatial distribution and thickness of the gaseous CO 2 derived from 3D seismic interpretation exhibit a generally good agreement with the simulation results (R 2 = 0.699 to 0.729). The present study successfully demonstrates how the integrated inverse modelling approach, applied for effective permeability calibration in a geological model here, can substantially reduce parameter uncertainty.

Spectral decomposition is a powerful tool that can provide geological details dependent upon discrete frequencies. Complex spectral decomposition using inversion strategies differs from conventional spectral decomposition methods in that it produces not only frequency information but also wavelet phase information. This method was applied to a time-lapse three-dimensional seismic dataset in order to test the feasibility of using wavelet phase changes to detect and map injected carbon dioxide within the reservoir at the Ketzin carbon dioxide storage site, Germany. Simplified zero-offset forward modelling was used to help verify the effectiveness of this technique and to better understand the wavelet phase response from the highly heterogeneous storage reservoir and carbon dioxide plume. Ambient noise and signal-to-noise ratios were calculated from the raw data to determine the extracted wavelet phase. Strong noise caused by rainfall and the assumed spatial distribution of sandstone channels in the reservoir could be correlated with phase anomalies. Qualitative and quantitative results indicate that the wavelet phase extracted by the complex spectral decomposition technique has great potential as a practical and feasible tool for carbon dioxide detection at the Ketzin pilot site. © 2016 European Association of Geoscientists & Engineers.

The geological storage of carbon dioxide (CO2) is the last link in the chain of Carbon Capture and Storage (CCS). CCS is, globally, regarded as one of the measures which need to be taken to reduce greenhouse gas emissions in order to limit global warming below 2°C, as agreed during the 2015 climate conference in Paris (COP21). During the past two decades, various storage projects at different scales were initiated, such as the Sleipner project in the Norwegian North Sea (commercial scale), the Illinois Decatur project (demo scale) or the Ketzin pilot site (pilot scale). As the first European onshore storage project, the Ketzin pilot site provided ideal conditions for demonstrating and testing a wide range of monitoring approaches. One of them was 4D seismic monitoring which was able to visualize the lateral propagation of the stored CO2 in the reservoir successfully. Monitoring data, such as the results of the seismic surveys, and reservoir pressure observations were used for setting up reservoir models as a basis for coupled process simulations at various time scales, enabling to predict long-term reservoir stabilization and to provide quantitative estimations of trapping mechanisms contributing to long-term stability.

The injection of CO2 at the Ketzin pilot site started in June 2008 and ended in August 2013. A total amount of about 67 kt of CO2 was injected into a saline aquifer. Aiming to investigate post-injection movement of the injected CO2, a third repeat 3D seismic survey, serving as the first post-injection survey was acquired in 2015. Consistent with the previous two monitoring surveys, a predominantly WNW migration of the gaseous CO2 plume in the updip direction within the reservoir is inferred in this first post-injection survey. There are no systematic anomalies detected through the reservoir overburden. The extent of the CO2 plume west of the injection site is almost the same as that one found in the 2012 second repeat survey (after injection of 61 kt). But there is a significant decrease in its size east of the injection site. The percentage of detected CO2 mass for the three seismic repeat surveys estimated using consistent input parameters shows a dramatically lower result for the third repeat than for the two surveys acquired during the injection period. Decrease in the size of the seismic anomaly may be explained as to be due to multiple factors, such as limited vertical resolution, CO2 dissolution and CO2 migration into thin layers, in addition to the effects of ambient noise. The assessments of various performance parameters comparing seismic monitoring and reservoir simulation results generally showed better conformance for the 2009 dataset than for the 2012 and 2015 datasets. The conformance assessment will be repeated with updated models after incorporating various new up-to-date monitoring data.

At the Ketzin pilot site for CO2 storage, from 2008 through 2013, 67,000 tons of CO2 were injected into the Triassic Stuttgart Formation, a saline aquifer at 630 m – 650 m depth. For continuous pressure and temperature monitoring over the whole depth range of the wells, a fibre optic cable was deployed in all deep injection and monitoring wells in the annulus outside the production casing. A VSP survey was acquired using a Mertz M12 vibro truck on 23 source points and using the whole length of deployed cable for recording. Seismic waves were recorded over a length of ~5900 m at a trace interval of 1 m. An inspection of the data quality shows that the signal to noise ratio is strongly affected by the coupling conditions of the cable. Within the cemented part of the casing, the coupling is reasonably good, whereas the signal to noise ratio is bad for uncemented intervals. In the lower half of the wells, coupling conditions are good enough to produce high-quality seismic shot gathers. These gathers were used for a 3D imaging of the reservoir complex used for CO2 storage in close vicinity to the injection and monitoring wells.

Elevated serum amino-transferase levels may be associated with liver injury. Testing for aspartate aminotransferase (AST) or alanine aminotransferase (ALT) is part of many routine screening approaches. The aim of this manuscript was to scrutinize the evidence for using ALT testing as a primary screening parameter for liver diseases. We conclude that (i) elevated serum ALT levels indicate a high specificity and a reasonable sensitivity liver injury, (ii) 10 - 25 % of German adults have elevated ALT levels, (iii) ALT values are increased in the majority but not all patients with acute and chronic liver disease (iv) elevated ALT-values are associated with an increased risk of liver-specific mortality, (v) elevated ALT values are also a risk factor for non-hepatic diseases including diabetes mellitus type 2, metabolic syndrome, cardiovascular diseases and malignancies, (vi) many liver diseases identified by an ALT screening can be treated successfully including prevention of development of clinical endpoints, (vii) an ALT-screening is very likely to be cost-effective although studies are needed for Germany to support this conclusion.

Fibre-optic Distributed Acoustic Sensing (DAS) or Distributed Vibration Sensing (DVS) is a technology, where an optical fibre cable is used as a sensor for acoustic signals. An ambient seismic wavefield, which is coupled by friction or pressure to the optical fibre, induces dynamic strain changes along the cable. The DAS/DVS technology offers the possibility to record an optoelectronic signal which is linearly related to the time dependent local strain. The DAS/DVS technology is based on the established technique of phase-sensitive optical time-domain reflec- tometry (phi-OTDR). Coherent laser pulses are launched into the fibre to monitor changes in the resulting elastic Rayleigh backscatter with time. Dynamic strain changes lead to small displacements of the scattering elements (non-uniformities within the glass structure of the optical fibre), and therefore to variations of the relative phases of the backscattered photons. The fibre behaves as a series of interferometers whose output is sensitive to small changes of the strain at any point along its length. To record the ground motion not only in space but also in time, snapshots of the wavefield are created by repeatedly firing laser pulses into the fibre at sampling frequencies much higher than seismic frequencies. DAS/DVS is used e.g. for continuous monitoring of pipelines, roads or borders and for production monitoring from within the wellbore. Within the last years, the DAS/DVS technology was further developed to record seismic data. We focus on the recording of Vertical Seismic Profiling (VSP) data with DAS/DVS and present an overview of various field tests published between 2011 and 2014. Here, especially CO2 storage pilot sites provided the oppor-tunity to test this new technology for geophysical reservoir monitoring. DAS/DVS-VSP time-lapse measurements have been published for the Quest CO2 storage site in Canada. The DAS/DVS technology was also tested at the CO2 storage sites in Rousse (France), Citronelle (USA), Otway (Australia) and Ketzin (Germany). At Ketzin it was possible to record a multi-offset VSP simultaneously within four wells, allowing a high-resolution imaging of the reservoir. These publications represent a wide range of different source types, source-receiver geometries and cable deployments (on tubing, behind casing). In conclusion, the DAS/DVS is a promising technology for VSP acquisition; the publications showed that it is possible to use DAS/DVS-VSP data for the calculation of velocity profiles, for well-ties and for seismic imaging. Some points have to be taken into account when recording DAS/DVS-VSP data. With an optical fibre, only a single value reflecting the strain between two points within the fibre is measured. The sensitivity of the fibre-optic cable is generally lower than that of a geophone with current readout units. If a fibre-optic cable has already been installed in a well, no well intervention is needed to acquire a VSP on demand, e.g. for time-lapse measurements. Several wells can be interrogated at the same time with full vertical coverage.

When CO2 replaces brine as a free gas it is well known to affect the elastic properties of porous media considerably. 3D seismic time-lapse surveys (4D seismics) have proven to be a suitable technique for monitoring of injected CO2. Forward modeling of a 4D seismic response to the CO2 fluid substitution in a storage reservoir is an important step in such studies. In order to track the migration of CO2 at the Ketzin pilot site (Germany), 3D time-lapse seismic data were acquired by means of a baseline (pre-injection) survey in 2005 and the monitor surveys in 2009 and 2012. Results of 4D seismic forward modeling with the reflectivity method suggest that effects of the injected CO2 on the 4D seismic data at the Ketzin pilot site are significant regarding both seismic amplitudes and time delays. They prove the corresponding observations in the real 4D seismic data at the Ketzin pilot site. However reservoir heterogeneity and seismic resolution, as well as random and coherent seismic noise are negative factors to be considered while the interpretation. In spite of these negative factors, results of 4D seismic forward modeling with the reflectivity method support the conclusion that the injected CO2 can be monitored at the Ketzin pilot site both qualitatively and quantitatively.

The Ketzin test site, Germany, is Europe's longest operating on-shore CO2 storage site. Between 06/2008 and 08/2013 about 70 kt of CO2 were injected in an anticlinal structure. The target reservoir is a sandstone saline aquifer at ~630-650 m depth. To enhance the understanding of the structural geometry of the site and to investigate the extension of the CO2 plume, several geophysical monitoring methods are applied at the Ketzin site, among which are seismics, geoelectrics and borehole measurements. Here, we focus on seismic methods, both surface a s well as zero-offset VSP. Prior to injection the baseline surveys of 3D seismic and zero-offset VSP were measured in 2005 and 2007, respectively. The 1st repeat measurements of 3D surface seismics were performed in 2009 after injection of about 22 kt of CO2, followed by the repeat of zero-offset VSP in 2011 after 46 kt of CO2 injection. The 2nd repeat of 3D surface seismic was measured in 2012 after about 61 kt of CO2 were stored in the target formation. Interpretation of these measurements allowed the ch aracterization of the CO2 plume's geometry and westward propagation direction. The amplitude variation is situated at the top of the reservoir near the injection well with a lateral extent of ~300-400 m after 1st repeat and ~400-600 m after 2nd repeat survey and a thickness of about 5-20 m. The amplitude anomaly matches the expected distribution of the CO2 plume derived from reservoir simulations, considering detection limits of seismic surface measurements. To increase the resolution and reliability of th e data, to improve the estimation of rock properties, and especially to enhance the imaging resolution of the CO2 plume, the time-lapse 3D seismic and zero-offset VSP data have been inverted for acoustic impedances. The applied inversion algorithms were Model Based Inversion and Band Limited Impedance Inversion for the 3D surface seismic and zero-offset VSP, respectively. The surface data and obtained impedances are compared with time-lapse VSP measurements and results of their inversion. The zero-offset VSP is inserted into an inline of 3D surface seismic crossing the receiver well, what makes a direct comparison of time-lapse amplitude difference and impedances possible. The comparison shows good agreement between these datasets regarding the impedances values. The high-resolution zero-offset VSP data complement the lateral image of the CO2 plume derived from 3D surface seismic in the vicinity of the well.

As part of the seismic monitoring at the Ketzin CO2 storage site, time-lapse VSP data were acquired. The purpose of the VSP experiment was to complement 3D surface seismic data with higher spatial resolution in close vicinity to the injection well. More than 45 kt of CO2 were injected between the baseline and repeat VSP surveys. For each VSP survey, data were measured at one zero-offset and seven offset source locations around the injection site with offsets varying between 282 m and 907 m. The VSP was recorded in a vertical well using an 80 level 3C geophone string extending 325 – 720 m below ground level, with an interval of 5 m between the levels. The CO2 was injected into a saline sandstone reservoir in 630 – 650 m depth. The injection well has a distance of 112 m to the recording well. Processing and interpretation of the offset VSP data comprises the following steps: (1) Seismic elastic FD modelling based on well log data. (2) Time-lapse processing of the modelled and measured data (application of a shaping filter on the repeat data to match the traces of the baseline data, removal of downgoing waves by fk-filtering). (3) Imaging of the data with 2D Kirchhoff and 2D Fresnel migration. (4) Comparison of the VSP with 3D surface seismic data. Processing and interpretation of the zero-offset VSP comprises the following steps: (1) Seismic elastic FD modelling based on well log data and results of the band limited impedance inversion. (2) Processing of the modelled and measured data (removal of downgoing and enhancement of upgoing waves by median filtering, application of an outside corridor to account for propagation effects of upgoing waves, such as multiples). (3) Band limited impedance inversion of the measured, modelled and 3D surface seismic data. (4) Comparison of the VSP with 3D surface seismic data. The offset VSP is comparable to the 3D surface seismic for both imaging methods, the 2D Kirchhoff and the 2D Fresnel migration. The time-lapse data show the CO2 signature in the depth range of the reservoir for those imaging planes crossing the CO2 plume. The zero-offset VSP time-lapse data show strong amplitudes in the depth range of the reservoir caused by the injection of CO2. The time-lapse amplitude of the modelled data is weaker than that of the measured data. Seismic velocities derived from the impedances indicate a velocity reduction of 30 %. Thus, time-lapse VSP imaging at Ketzin shows that monitoring of small injection amounts is feasible.

At the Ketzin pilot site, CO2 is being injected since 2008 in a sandstone aquifer at depths of approx. 630-650 m. As a part of a comprehensive geophysical monitoring program, 4D seismic surveys were acquired. The baseline measurement was carried out in 2005 and the 1st repeat in 2009, after 22000 tons of CO2 were injected in the target reservoir. The difference of the surveys revealed a time-lapse signature associated with the injected CO2, which matches the expected distribution of the plume derived from reservoir simulations. In scope of long-term low-cost monitoring, the possible sparsity of geometries for 2D seismic surveys, which still would enable imaging of the CO2 distribution, were investigated. The baseline and repeat seismic surveys were modeled for a set of sparse geometries and time-lapse effects were analyzed regarding the visibility of the CO2 signature, which is the focus of this presentation. For building 3D elastic models of the subsurface, the results of the acoustic impedance (AI) inversion of baseline and 1st repeat data sets, obtained in a previous study , were used. The P-velocity and density distributions were calculated from the AI-cubes with the Gardner’s equation. Since no S-velocity cube was available, the Vp-cube and the Castagna’s relationship obtained from logs were used for calculation of the required Vs-model. The same Vs-model was used for modelling of baseline and repeat data, as no changes in the S-velocities due to the CO2 injection are expected. The difference cubes, both from measured data and from inverted impedances, show besides the CO2 signature also a noisy background and some features owing mostly to the processing artifacts and acquisition. Within the modelling, these differences can approximate noise level which can be expected on the real processed data.

The Common Reflection Surface, or CRS technique offers a comprehensive workflow for improving seismic processing, imaging, and reservoir characterisation in time and depth, which has been demonstrated in a project of geological CO2 storage at the Ketzin site in Eastern Germany. In applications to the 3D seismic baseline data that was acquired before CO2 injection, the results of the CRS time processing chain are compared to a previous conventional processing. The CRS noise suppression and regularization in the prestack data result in the so-called CRS gathers where acquisition related data gaps and fold variation are compensated for using the lateral event continuation of the CRS method. Both, the data reconstruction and the enhanced prestack signal quality lead to an increased resolution of the subsurface image, and strongly improve the tie to the well data. In the mapping of shallow gas at extremely low fold at this time level, CRS-based AVO resolves a well defined outline and inner structure of the gas zone, and clearly discriminates high-amplitude events outside the gas zone. The CRS technique thus proves to be a versatile tool for improved structural assessment and reservoir monitoring in both, storage and exploration projects.

Elevated serum amino-transferase levels may be associated with liver injury. Testing for aspartate aminotransferase (AST) or alanine aminotransferase (ALT) is part of many routine screening approaches. The aim of this manuscript was to scrutinize the evidence for using ALT testing as a primary screening parameter for liver diseases. We conclude that (i) elevated serum ALT levels indicate a high specificity and a reasonable sensitivity liver injury, (ii) 10 - 25 % of German adults have elevated ALT levels, (iii) ALT values are increased in the majority but not all patients with acute and chronic liver disease (iv) elevated ALT-values are associated with an increased risk of liver-specific mortality, (v) elevated ALT values are also a risk factor for non-hepatic diseases including diabetes mellitus type 2, metabolic syndrome, cardiovascular diseases and malignancies, (vi) many liver diseases identified by an ALT screening can be treated successfully including prevention of development of clinical endpoints, (vii) an ALT-screening is very likely to be cost-effective although studies are needed for Germany to support this conclusion.

In standard KPSDM implementations of Kirchhoff prestack depth migration (KPSDM) the wavefield is smeared along two-way-traveltime isochrones. In the case of sparse sampling or limited aperture the image is sometimes affected by significant migration noise. Some modifications have been proposed which aim at reducing these artefacts by constructing a specular path of wave propagation derived from the slowness of coherent phases in the seismogram section and the heuristic restriction of the imaging operator to that wave path. Here we propose another physically frequency-dependent approach by using the concept of Fresnel-Volumes. Firstly the emergence angle at the receiver is determined by a local slowness analysis. Using the emergence angle as the starting direction a ray is propagated into the subsurface and the back-propagation of the wavefield is restricted to the vicinity of this ray according to its approximated Fresnel-Volume. We describe the procedure and show applications to a synthetic model as well as a real data set over a salt pillow in North Germany. Compared with standard KPSDM the image quality of our Fresnel-Volume-Migration is significantly enhanced due to the restriction of the migration operators to the region near the actual reflection point.

[1] A 400-km-long seismic reflection profile (Andean Continental Research Project 1996 (ANCORP'96)) and integrated geophysical experiments (wide-angle seismology, passive seismology, gravity, and magnetotelluric depth sounding) across the central Andes (21°S) observed subduction of the Nazca plate under the South American continent. An east dipping reflector (Nazca Reflector) is linked to the down going oceanic crust and shows increasing downdip intensity before gradual breakdown below 80 km. We interpret parts of the Nazca Reflector as a fluid trap located at the front of recent hydration and shearing of the mantle, the fluids being supplied by dehydration of the oceanic plate. Patches of bright (Quebrada Blanca Bright Spot) to more diffuse reflectivity underlie the plateau domain at 15–30 km depth. This reflectivity is associated with a low-velocity zone, P to S wave conversions, the upper limits of high conductivity and high Vp/Vs ratios, and to the occurrence of Neogene volcanic rocks at surface. We interpret this feature as evidence of widespread partial melting of the plateau crust causing decoupling of the upper and lower crust during Neogene shortening and plateau growth. The imaging properties of the continental Moho beneath the Andes indicate a broad transitional character of the crust-mantle boundary owing to active processes like hydration of mantle rocks (in the cooler parts of the plate margin system), magmatic underplating and intraplating under and into the lowermost crust, mechanical instability at Moho, etc. Hence all first-order features appear to be related to fluid-assisted processes in a subduction setting.