A B S T R A C TThe seismic K-Horizon is the key to gaining understanding on the deep supercritical geothermal rocks in Southern Tuscany. The K-Horizon is hosted in metamorphic rocks, which cause strong seismic wavefield scattering resulting in a poor signal-to-noise ratio. Our study aims to reveal high-resolution seismic images of the K-Horizon below a geothermal field in Southern Tuscany, using an advanced threedimensional seismic depth imaging approach. The key seismic pre-processing steps in the time domain include muting a large amount of persistent noise based on the statistical analysis of the seismic amplitudes, and tomostatics technique to correct for static effects. We carried out seismic depth imaging using Kirchhoff Pre-Stack Depth Migration and Fresnel Volume Migration techniques. Each migration technique was tested with constant and heterogeneous three-dimensional velocity models. Due to the difficulties in determining emergent angles for this low signal-to-noise ratio data set, the migration results with the heterogeneous three-dimensional velocity model show less coherent reflections compared to the migration results using the constant velocity model. Both velocity models however lead to relatively the same structure and depth of the K-Horizon, indicating the similarity of the average velocities along the wave propagation paths in both velocity models. With both velocity models Fresnel Volume Migration yields the K-Horizon with better reflection coherency and higher signal-to-noise ratio than standard Kirchhoff Pre-Stack Depth Migration. Nevertheless, both migration techniques have been able to reveal the K-Horizon with relatively high resolution and provide a reliable basis for geothermal rock characterization as well as steering of the first geothermal well penetrating the K-Horizon.
Continental shelves around the globe are hosts to vast reservoirs of offshore freshened groundwater. These systems show considerable complexity, often as a function of the geological heterogeneity. Data needed to characterise these systems are often sparse, and numerical models rely on generalized simplifications of the geological environment. In order to improve our understanding of these systems, it is necessary to implement modelling approaches that can produce large-scale geologically representative models using sparse data. We present an interdisciplinary stochastic modelling workflow incorporating borehole data, 2D depth-migrated seismic profiles, seismic attributes, and prior knowledge of the depositional setting. We generate a conditioned Gaussian field of porosity on the New Jersey shelf. We also perform a petrophysical conversion to a corresponding permeability distribution. The model dimensions are 134 km × 69 km × 1.7 km, with an adjustable resolution that can be adapted for process-based models of flow and solute transport. The integrated approach successfully translates small-scale porosity variations to a shelf-scale model that honors key characteristics of the New Jersey shelf wave-dominated depositional environment. The model was generated using open-source packages. All data and code to reproduce the complete workflow are provided along with this study so the model can be reproduced at any resolution for further studies of continental shelf processes offshore New Jersey.
<p>3D seismic measurements are a tool for high-resolution structural exploration of the subsurface using artificially generated seismic waves. Depending on the acquisition geometry and the seismic source, structures can be examined at depths ranging from a few meters to more than 10 km. The accuracy of the geological layer boundaries in the depth image resulting from the field data depends heavily on the quality and the details of the physical earth model and the imaging algorithms used.</p>
<p>The "DOSIS" project was initiated in order to design an optimized, combined and high-resolution method to facilitate finding answers for important geophysical and geological questions in the exploration of repository sites in Germany in the future. In the framework of the "DOSIS" project, the simulation of elastic waves using finite differences and the associated full-waveform inversion as well as the Fresnel-volume migration are further developed, so that seismic anisotropy and inelastic attenuation can be taken into account for a detailed characterization of the subsurface. These methods are tested and validated using both, synthetic data and real data in the form of a massive high-quality 3D seismic data set acquired in 2020 in the area of the "Asse" salt structure in Lower Saxony and provided by BGE.</p>
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