Seismic depth imaging of a geothermal system in Southern Tuscany

Abstract

A B S T R A C TThis work represents a case study concerning the application of reflection seismic imaging methods in the context of geothermal exploration. Our goal is to obtain accurate structural images of a geothermal active area in southern Tuscany. These images will be required in subsequent studies as the input for geological model building and numerical simulation of the heat transport and fluid flow. The target region exhibits great geologic complexity, including strong velocity contrasts, lateral nearsurface inhomogeneities, fracture zones, and significant topography. Those features are typical for a volcanic hard-rock environment and pose significant challenges to conventional seismic imaging methodology. Therefore, we apply a sophisticated and robust depth imaging workflow to previously acquired surface seismic data. Within our workflow, we focus on estimating the seismic velocities of the predominant rock units and subsequently carry out Kirchhoff pre-stack depth migration and Fresnel volume migration to obtain high-resolution images of the subsurface. Our results demonstrate that the applied methodology provides a valueable tool for imaging in a complex environment such as a volcano-geothermal area. In detail, the resulting reflector images show the main horizons that delineate the Tuscan sedimentary rocks in the target region. The images from standard Kirchhoff migration can be significantly enhanced by utilizing Fresnel volume migration, which eliminates migration artefacts and provides a better result. Moreover, we obtain the migration velocities and depths for an important regional reflector, known as the K-horizon, which is of major interest for geothermal characterization.

Influence of depth, temperature, and structure of a crustal heat source on the geothermal reservoirs of Tuscany: numerical modelling and sensitivity study

“…However, the strength of the refection signal varies considerably along the profiles with local ambiguities and offsets (Riedel et al 2015). Similar phenomena have been observed in other seismic profiles which resolve the K horizon where "multiple reflections and complex appearance due to interconnecting reflections, refractions, and diffraction" have been reported (Gianelli et al 1997).…”

“…3). In an alternative interpretation by Riedel et al (2015), this stacking does not exist. Instead, the Burano unit west of the major fault is considered to be very thick, which may affect the thermal regime in that area.…”

“…A seismic depth migration analysis of the time-recorded reflection signals leads to uncertainty in position that increases with depth. The K horizon in the study area is deeper than 5 km, and the uncertainty in determining its depth given the available information has been estimated to be approximately 300m (Riedel et al 2015).…”

Advanced three‐dimensional seismic imaging of deep supercritical geothermal rocks in Southern Tuscany

“…; Riedel et al . ; Hloušek and Buske ). Some of these studies also emphasized the advantage of FVM over standard KPSDM (Lüth et al .…”

The 1d Velocity Model Using the Deep Seismic Sounding (Dss) Data and Local Earthquake Data Under Equal Conditions of the Experiment

“…, для моделирования геометрии геотермальных источников [2], для понимания процессов, происходящих в очаговых зонах [3], картирования зон разломов [4], флюидонасыщенности среды [5], для поиска полезных ископаемых [6], для обеспечения априорной информации о геологической среде других методов разведки [7].…”