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A 2D vibroseis line was acquired in the Vienna Basin (Austria) for the purpose of comparing the data of digital multicomponent single sensors based on microelectromechanical system (MEMS) sensors alongside conventional vertical-component geophone arrays. For efficient removal of coherent noise during processing, all source points were recorded in single-sweep mode, i.e., no vertical stacking was performed in the field. On this densely sampled data set, several noise-reduction techniques, such as digital array forming, frequency-wavenumber (f-k) filtering in shot and receiver domains, and polarization filters, proved to be valuable in reducing source-generated noise. The results showed that, with the use of single-sweep recording and polarization filter techniques, it is possible to produce seismic sections for a singlereceiver three-component (3C) MEMS line that are comparable to a conventional geophone array line in signal-to-noise ratio. However, the higher number of single geophones and hence the stronger attenuation of random noise in the conventional array resulted in an advantage for the analog geophone data set. The second goal for this survey was to evaluate additional information contained in the horizontal components of the MEMS data. The multicomponent data allowed for the processing of mode-converted shear-wave data, performed for the first time in the Vienna Basin. Azimuthal anisotropy related to horizontal stresses was observed in the Neogene section of the shear-wave data set. A PP-PS event correlation allowed the identification of major shallow horizons. Interpretation of the final sections confirmed that the PS data are useful to distinguish between gas reservoirs and high-porosity water sands, which can cause similar P-wave amplitude variation with offset (AVO) effects.

We present a case study for designing a passive seismic monitoring network in a large underground gas storage site. The study included measurements of background seismic noise at selected locations across the site and background seismic noise along a string of receivers cemented in a shallow monitoring borehole. We measured the noise levels over a period of three months and studied the background seismic noise reduction in the shallow monitoring borehole. Specifically this study reveals a significant decrease with depth of the temporal variations in background seismic noise levels at the shallow monitoring borehole relative to the surface. We compare location accuracy from the downhole and surface monitoring arrays, and combinations of these to determine the optimal monitoring array. We also evaluate the detection threshold for microseismic events in the proposed shallow borehole monitoring array based on measured noise levels and empirical observations of microseismic events in similar reservoirs.

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