1 2In a geothermal area, a detailed knowledge of the three-dimensional velocity structures aids the 3 management of the field and the further development of the geothermal source. Here, we present a 4 high-resolution study of the three-dimensional S-wave velocity structures from microearthquake 5 travel times for the Larderello-Travale geothermal field, Italy. We have also deduced the Vp/Vs and 6 Vp*Vs parameters for this area to emphasize the deep variations in the physical rock properties due 7 to fluid content and porosity. Furthermore, effective porous medium modelling has been performed 8 for site-relevant lithologies, to improve our interpretation of the results in terms of rock physics 9signatures. This has allowed us to estimate the variation range of the seismological parameters 10 investigated, as well as their sensitivity for suitable rock under specific physical conditions. Low
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.
The cross-calibration of different vintage data is an important prerequisite in attempting to determine the time-lapse seismic effects induced by hydrocarbon production in a reservoir. This paper reports the preprocessing and cross-calibration procedures adopted to modify the data of four seismic vintages (1982, 1989, 1992 and 1999) from the Oseberg field in the North Sea, for optimal conditions for a time-lapse seismic amplitude analysis. The final results, in terms of time-lapse variations, of acoustic impedance and of amplitude-versus-offset, are illustrated for selected data sets. The application of preprocessing to each individual vintage data set reduces the effects of the different acquisition and noise conditions, and leads to consistency in the amplitude response of the four vintages. This consistency facilitates the final amplitude cross-calibration that is carried out using, as reference, the Cretaceous horizon reflections above the Brent reservoir. Such cross-calibration can be considered as vintage-consistent residual amplitude correction.Acoustic impedance sections, intercept and gradient amplitude-versus-offset attributes and coherent amplitude-versus-offset estimates are computed on the final cross-calibrated data. The results, shown for three spatially coincident 2D lines selected from the 1982, 1989 and 1999 data sets, clearly indicate gas-cap expansion resulting from oil production. Such expansion is manifested as a decrease in acoustic impedance and a modification of the amplitude-versus-offset trends in the apical part of the reservoir.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.