In this work we present a workflow to estimate a high-resolution acoustic velocity model of a seismic land dataset acquired in a geothermal exploration area. The data are characterized by poor S/N ratio and lack of reflections in the shallow part, above 2s. The model is obtained by exploiting the transmitted waves in a two-steps full-waveform inversion (FWI) approach. In the first, we perform a global FWI based on the genetic-algorithm (GA) optimization method. Making use of a large search range centered on a gradient-like velocity field, GA are used to estimate a low frequency velocity model. In the second step, the obtained model is used as the starting point for a gradient- based FWI. In the GA inversion we consider frequency lower than 10 Hz, while we extend the frequency up to 20 Hz in the local inversion, adopting a frequency marching scheme. The final velocity model shows an improved resolution in the shallow part of the subsurface. Its features, characterized by many details, can be employed directly as a geological interpretation tool. The reliability of the final velocity model is assessed by the data misfit achieved and by the comparison with the available VSP.
Use of Global-Local FWI of Seismic Land Data Acquired in a Geothermal Exploration Area
A. Tognarelli
;E. Stucchi;A. Mazzotti
2019-01-01
Abstract
In this work we present a workflow to estimate a high-resolution acoustic velocity model of a seismic land dataset acquired in a geothermal exploration area. The data are characterized by poor S/N ratio and lack of reflections in the shallow part, above 2s. The model is obtained by exploiting the transmitted waves in a two-steps full-waveform inversion (FWI) approach. In the first, we perform a global FWI based on the genetic-algorithm (GA) optimization method. Making use of a large search range centered on a gradient-like velocity field, GA are used to estimate a low frequency velocity model. In the second step, the obtained model is used as the starting point for a gradient- based FWI. In the GA inversion we consider frequency lower than 10 Hz, while we extend the frequency up to 20 Hz in the local inversion, adopting a frequency marching scheme. The final velocity model shows an improved resolution in the shallow part of the subsurface. Its features, characterized by many details, can be employed directly as a geological interpretation tool. The reliability of the final velocity model is assessed by the data misfit achieved and by the comparison with the available VSP.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.