| 1. |
- Kumar, Sandeep, et al.
(författare)
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Groundwater monitoring and characterization by a vertical dipole of superconducting gravimeters in a karst aquifer, France
- 2021
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Ingår i: SEG Technical Program Expanded Abstracts. - : Society of Exploration Geophysicists. - 1052-3812 .- 1949-4645. ; 2021-September, s. 889-893
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Konferensbidrag (refereegranskat)abstract
- The Earth's mass distribution is continuously changing due to physical processes taking place either beneath the subsurface or on the surface. Some of the primary sources for these mass variations are tides in the ocean and solid Earth, atmospheric disturbances and seasonal climate changes. The development of Superconducting Gravimeters (SGs) has made it possible to characterize and monitor such mass variations at micro scales. Our study focuses on the LSBB karst catchment's hydrodynamics using a unique configuration of two SGs located 520 m depth apart. The installation of a SG (iGrav-31) at the surface of the LSBB several years after the installation of the first (iOSG-24) inside the tunnel has provided several new insights into the understanding of hydrological processes occurring in the LSBB. In this work, we compare differential and residual gravity time-series together with the ERA5 global hydrological loading model. In the subsequent section, we implement a rectangular prism method to compute forward gravity responses using input from the hydrological model. We also numerically evaluate and validate the already published hypotheses (Mouyen et al., 2019) about uncertainties related to groundwater storage's location in this catchment. Based on our observations, we find that most water-storage changes occur in the unsaturated karst zone between both SGs. The misfit between the residual gravity time-series and the local hydro-gravity effect computed from ERA5 model shows large lateral fluxes and rapid runoff occurring in the LSBB. Finally, we conclude this work by examining the radial and depth sensitivity of water masses' effect near the SGs, and enlisting some recommendations for further studies.
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| 2. |
- Aderemi, Adetomiwa, et al.
(författare)
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Porosity and permeability calculations in a Biolithite using x-ray tomography images
- 2023
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Ingår i: SEG Technical Program Expanded Abstracts. - 1052-3812. ; 2023-August, s. 1700-1704
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Forskningsöversikt (refereegranskat)abstract
- Engineering energy storage/extraction for geoenergy applications (e.g., geothermal energy extraction, CO2 and/or Hydrogen storage) requires a very good knowledge of subsurface heterogeneities. One of the principal factors that influences the response of the underground system is the continuously evolving pore networks of the targeted rocks. This work aims to understand the pore network of a natural Biolithite (Figure 1), coming from a Greek outcrop, and to predict the permeability of lab-scale systems (due to diagenetic alterations and/or natural deformation) using x-ray computed tomography (CT) images (3D) and stochastic model reconstructions. We emphasize on the importance of a reproducible image analysis workflow (Figure 2) during reservoir description, as an input to extracting pore network models that have representative geometrical and topological characteristics at core-plug scale.
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| 3. |
- Andersson, Fredrik, et al.
(författare)
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Fixed point algorithms for detection of parabolic events
- 2016
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Ingår i: SEG Technical Program Expanded Abstracts. - : Society of Exploration Geophysicists. - 1052-3812. ; 35, s. 3997-4002
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we show how to convert the problem of estimating delay, slope and curvature of a parabolic event into a frequency estimation problem. Two dimensional data (time and offset) is converted into samples on a two-dimensional manifold embedded in a three-dimensional spaced. To conduct frequency estimation on this manifold we design general domain Hankel matrices and make use of a fixed point algorithm that is designed to find minima of convex envelopes of functionals using a combination of a rank penalty and a misfit function, under the constraint of a certain matrix structure. We illustrate that the proposed method can successfully detect the parameters of the parabolic events also in the case of unequally spaced spatial sampling and in the presence of rather high levels of noise.
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| 6. |
- Dahlin, Torleif, et al.
(författare)
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Geophysical mapping of aquifers in Bolivia
- 2017
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Ingår i: Procs. SEG Technical Program Expanded Abstracts 2017, 24-27 September 2017, Houston. - : Society of Exploration Geophysicists. - 1052-3812. ; , s. 5317-5321
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Konferensbidrag (refereegranskat)abstract
- Electrical Resistivity Tomography (ERT) and Transient ElectroMagnetic sounding (TEM) is used for aquifer mapping in Bolivia. The results demonstrate the value of using geophysics in hydrogeological investigations of quaternary deposits, and that the methods are complementary so that the combination is beneficial. ERT produced highly useful results for delineating the aquifer geometry and internal aquifer structure, detect variations in sediment composition and locate areas with anomalous water composition. ERT proved to be very robust despite possible sources of disturbances in the form of powerlines and other infra structure. The depth penetration is however not always sufficient with the spreads mostly used here. TEM proved to be useful for reaching larger depths, although the application of the method is restricted in parts of the areas due to various man-made objects that cause coupling problems. TEM delimitated a rather thin saline layer at the base of the Punata aquifer, which will contribute to enhance the local groundwater management and exploitation.
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| 7. |
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| 8. |
- Duchkov, Anton A., et al.
(författare)
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Sparse wave-packet representations and seismic imaging
- 2010
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Ingår i: SEG Technical Program Expanded Abstracts. - : Society of Exploration Geophysicists. - 1052-3812. ; 29:1, s. 3318-3322
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Konferensbidrag (refereegranskat)abstract
- In this paper we introduce a new algorithm for seismic imaging based on the flow out of Gaussian wave packets. We follow the standard strategy of decomposing data into wave packets and flowing them out along rays to approximate the downward wavefield extrapolation, and finally applying an imaging condition. We revisit each computational step to gain efficiency. Furthermore, we develop procedure for seismic data decomposition in order to obtain highly sparse representations with Gaussian wave packets. As a result we get fast algorithm heavily exploiting sparse data representation and analytic description of Gaussian wave packets. We tests our algorithm on synthetic example of migrating common-shot gather.
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| 9. |
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| 10. |
- Engquist, Björn, et al.
(författare)
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Sweeping preconditioner for 3D Helmholtz equation
- 2011
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Ingår i: Society of Exploration Geophysicists. Expanded Abstracts with Biographies. - : Society of Exploration Geophysicists. - 1052-3812. ; 30:1, s. 3158-3163
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Tidskriftsartikel (refereegranskat)abstract
- TheHelmholtz equation describes wave propagation in the frequency domain and,as such, can be used for seismic imaging and fullwaveform inversion. We present two novel preconditioners for the efficientsolution of the Helmholtz equation in three dimensions. Both methodsfollow the general structure of constructing an approximate LDLt factorizationby eliminating the unknowns layer by layer starting from anabsorbing layer or boundary condition. In the first approach, werepresent the Schur complement matrices of the factorization in thehierarchical matrix framework. In the second approach, applying each Schurcomplement matrix is equivalent to solving a quasi-2D problem withthe multifrontal method. These preconditioners have linear application cost, andthe preconditioned iterative solvers converge in a number of iterationsthat is essentially independent of the number of unknowns orthe frequency. Numerical results on realistic 3D seismic models toconfirm the efficiency of these methods.
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