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  • 1
    Publication Date: 2012-12-19
    Description: Theoretical work and modelling studies have led to the hypothesis that the ambient seismic wave field on the surface can be affected by hydrocarbon reservoirs (〉800 m depth). Several field studies have linked spectral features on the vertical component between 1 and 10 Hz to reservoir locations. However, such evidence has been criticized due to concerns that surface recordings typically contain a large amount of surface wave noise and correlations to hydrocarbon targets could be caused by non-hydrocarbon variables such as topography or weathering layer thickness. In this paper, we suggest a two-step analysis strategy to address such issues. First, spectral power is only averaged over time periods and frequencies where the distribution of polarization attributes show no obvious dominance of a few surface wave sources. An interferometric test reveals differences in the wave field composition between the filtered and unfiltered data. Second, the residual seismic power is correlated to hydrocarbon as well as non-hydrocarbon targets. The correlations are quantitatively compared using rank correlation and bootstrap confidence intervals. The method is illustrated on a passive seismic data set acquired with three-component, broad-band seismometers at the tight-gas Jonah field in Wyoming, USA. We find evidence that the wave field was dominated by a small number of surface sources in all of the data except for the quietest time periods in the low-frequency range 1.5–3.0 Hz. Seismic power within this subset significantly correlates to a published reservoir map but not with a digital elevation model and less so with an infrastructure density map. The investigated hypothesis can thus not be rejected with this data.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 2
    Publication Date: 2014-06-21
    Description: Samples of shales from the Ordovician Bongabinni and Goldwyer source rock formations were recovered from the Canning Basin (Western Australia). Attenuation was experimentally measured on preserved plugs from these formations in the frequency range between 10 –2 and 10 2 Hz. Samples cored with different orientations with respect to the sedimentary bedding were prepared and tested in their native saturated state and after drying in the oven at 105 °C for 24 hr to assess the effect of fluids and of the sediment anisotropy on attenuation. To aid the interpretation of the experimental results, the clay-rich samples were characterized in terms of mineralogy, water content, porosity, permeability and microstructure. The two shales have significantly different quality factors; and this is seen to be dependent on both the saturation state of the samples and the propagation direction of the oscillatory signal. The attenuation coefficient for compression/extension parallel to bedding is less than that vertical to bedding in both the preserved and partially dehydrated situations. No frequency dependency is observed in the preserved samples within the range of frequencies explored in this study. On the other hand partially saturated samples show peaks in attenuation at around 40 Hz when the stress perturbation is transmitted normal to the macroscopic bedding. The interpretation of the attenuation measurements in terms of well-established theoretical models is discussed in view of the physical characteristics and microstructure of the tested rocks.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Lung 61 (1925), S. 504-508 
    ISSN: 1432-1750
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Zusammenfassung Es gelingt, mit dem vonLanger angegebenen Impfstoff in der überwiegenden Anzahl der Fälle gegen Tuberkulin zu allergisieren. Versager lassen sich vermutlich auf zu lang gelagerten Impfstoff zurückführen. Damit werden die vonSelter erhobenen Einwände gegen dasLangersche Allergisierungsverfahren hinfällig. Gerade die langsam eintretende, ständig zunehmende Allergisierung spricht sehr für dieLangersche Methodik und rechtfertigt unseres Erachtens durchaus, gefährdete Säuglinge im ersten Lebensjahre mit dem ImpfstoffLangers zu immunisieren, zumal Schädigungen nicht zu erwarten sind. Dagegen führten Versuche, per os gegen Tuberkulin zu allergisieren, in der überwiegenden Mehrzahl der Fälle zu keinem irgendwie praktisch verwertbaren Ergebnis.
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 2021-01-26
    Description: We present a 1D shear‐velocity model for Los Humeros geothermal field (Mexico) obtained from three‐component beamforming of ambient seismic noise, imaging for the first time the bottom of the sedimentary basement ∼5km below the volcanic caldera, as well as the brittle‐ductile transition at ∼10km depth. Rayleigh‐wave dispersion curves are extracted from ambient seismic noise measurements and inverted using a Markov chain Monte Carlo scheme. The resulting probability density function provides the shear‐velocity distribution down to 15 km depth, hence, much deeper than other techniques applied in the area. In the upper 4 km, our model conforms to a profile from local seismicity analysis and matches geological structure inferred from well logs, which validates the methodology. Complementing information from well logs and outcrops at the near surface, discontinuities in the seismic profile can be linked to geological transitions allowing us to infer structural information of the deeper subsurface. By constraining the extent of rocks with brittle behavior and permeability conditions at greater depths, our results are of paramount importance for the future exploitation of the reservoir and provide a basis for the geological and thermodynamic modeling of active superhot geothermal systems, in general.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 5
    Publication Date: 2020-02-12
    Description: Extensive passive seismic monitoring was carried out between September 2017 and September 2018 over the Los Humeros geothermal field in Mexico. This experiment, in addition to several geophysical, geological, and geochemical surveys was conducted in the framework of the European H2020 and Mexican CONACyT-SENER project GEMex for a better understanding of the structures and behavior of the local geothermal system currently under exploitation, and for investigating future development areas. 25 broadband stations (22 Trillium C-120s and 3 Trillium C-20 PH) recording at 200 Hz, and 20 short period stations (Mark L-4C-3D) recording at 100 Hz comprised the network which is sub-divided into two sub-networks. An inner and denser (~1.6-2 km inter-station distance) pseudo-rhomboidal array (27 stations) was laid out to cover the producing zone and retrieve local seismicity mainly associated to injection and production operations, and to comply with beamforming of ambient noise and time reverse imaging techniques. An outer and sparser (~5 km minimum spacing) array was placed at around 30 km radius surrounding the inner network, and was mainly dedicated to larger scale imaging techniques, such as seismic ambient noise tomography, and regional earthquakes tomography. The GEMex project is supported by the European Union’s Horizon 2020 programme for Research and Innovation under grant agreement No 727550 and the Mexican Energy Sustainability Fund CONACYT-SENER, project 2015-04-68074. Waveform data are available from the GEOFON data centre, under network code 6G, and are embargoed until January 2023.
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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  • 6
    Publication Date: 2020-02-12
    Description: Passive seismic low-frequency from approximately 1–6 Hz data have been acquired at several locations around the world. Spectra calculated from these data, acquired over fields with known hydrocarbon accumulations, show common spectral anomalies. Verification of whether these anomalies are common to only a few, many, or all hydrocarbon reservoirs can be provid-ed only if more and detailed results are reported. An extensive survey was carried out above a tight gas reservoir and an adjacent exploration area in Mexico. Data from several hundred stations with three-component broadband seismometers distributed over approximately 200 km 2 were used for the analysis. Several hydrocarbon reservoir-related microtremor attributes were cal-culated, and mapped attributes were compared with known gas intervals, with good agreement. Wells drilled after the survey confirm a predicted high hydrocarbon potential in the explora-tion area. A preliminary model was developed to explain the source mechanism of those microtremors. Poroelastic effects caused by wave-induced fluid flow and oscillations of different fluid phases are significant processes in the low-frequency range that can modify the omnipresent seismic background spectrum. These processes only occur in partially saturated rocks. We as-sume that hydrocarbon reservoirs are partially saturated, where-as the surrounding rocks are fully saturated. Our real data obser-vations are consistent with this conceptual model.
    Type: info:eu-repo/semantics/article
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  • 7
    Publication Date: 2020-02-12
    Type: info:eu-repo/semantics/conferenceObject
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  • 8
    Publication Date: 2020-02-12
    Type: info:eu-repo/semantics/article
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  • 9
  • 10
    Publication Date: 2021-12-22
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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