Low-frequency anomalies in spectral ratios of single station microtremor measurements: Observations across an oil and gas field in Austria
Published in
SEG/San Antonio 2007 Annual Meeting
Publication date
25 September 2007
Abstract
We investigate spectral ratios of the microtremor wavefield in the low frequency range (< 10 Hz) above and nearby hydrocarbon reservoirs. The spectral ratios are calculated from the different components of ground motion measured at single stations. An example of such a ratio in the literature is the horizontal-to-vertical spectral ratio (H/V-ratio). We elaborate the spectral ratio technique to detect and characterize hydrocarbon bearing structures. Our focus is on the peak amplitude of the V/H-ratio in the low frequency range, and we map this attribute along three profiles across an oil and gas field near Voitsdorf, Austria. Characteristic modifications across the hydrocarbon reservoir are observed, namely that higher values and larger variations of the peak amplitude occur above the reservoir. A finite difference model for seismic wave propagation produces similar patterns in the V/H-ratio. The model assumes vertical force variations within the reservoir to be the mechanism responsible for the observed phenomenon. The results of this case study indicate that spectral ratios of microtremors may contain useful information to detect and characterize hydrocarbon bearing structures in the subsurface.
