GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.2 149 of vintage seismic reflection lines can be poor due to several reasons: very different acquisition periods (over 30 years, since 1970) that means different equipments, technologies and acquisition configuration used (e.g. Vibroseis or dynamite sources, different CDPs folding and acquisition parameters etc..). In spite of this, such kind of dataset represents, at the present day, an unrepeatable opportunity in terms of seismic records. Moreover, availability of raw data from oil and gas companies offers a valuable possibility for reprocessing through more modern techniques (Stucchi et al. , 2006) or for seismic attribute analysis (Taner et al. , 1979). The potential andbenefits of a seismic attributes applicationare continuously improving due to the increasing power of PCs and to the continuous developments of new attribute algorithms (Chopra and Marfurt, 2008), with some interesting application even on GPR data (Ercoli et al. , 2015, 2012). In this work, we present a first application on the aforementioned seismic lines, in order to provide new data through an improved visualization. We computed instantaneous amplitude, phase and frequency attributes, to allow the interpreters producing a better and more efficient interpretation of the main geologic units and discontinuities. Data and method. The dataset encompasses almost 85 unpublished 2D seismic reflection profiles located along and across the entire study area. Here, we present the first results obtained along a transect crossing the Apennines at the Castelluccio di Norcia basin. The seismic SEG-Y files were loaded into the GPL OpendTect software (http://dgbes. com/), by using stored CDP coordinates and a common seismic datum. The seismic profiles belonging to this ENE- WSW transect show subsurface features down to a depth of 5 s (twt, corresponding to 10–12 km), that allow us to infer a new subsurface geological model. Attribute analysis methods may allow to evaluate (http://doc.opendtect.org ): - strong reflective layers and signal strength, through the “ InstantaneousAmplitude ” (orTrace Envelope and “ Energy ”), as a discriminator for acoustic impedance contrasts, sequence boundaries, bed thickness and thin-beds, spatial correlation lithologic variations; - spatial continuity and discontinuity of reflections, through the “ Instantaneous Phase ”, making strong events clearer and emphasizing discontinuities like faults, pinch-outs etc. Among the instantaneous phase attributes family, the “ Cosine of the Instantaneous Phase ” (or “normalized amplitude”) has the benefit to be continually smooth, providing the +/- 180 degree discontinuity, so that strong and weak events exhibit equal strength; - low frequency anomalies as fracture zone indicator and bed thickness indicator, through the “ Instantaneous Frequency ”, higher frequencies and lower frequencies suggest sharp interfaces (e.g. thinly laminated shales), and massive bedding geometries, respectively; - another interesting attribute is represented by the “ Pseudo-Relief ”, particularly useful in 2D seismics, allowing to create a more consistent image for an easier interpretation of faults and horizons. It consists in two steps: a first “Energy” attribute (RMS amplitude) computation is followed by the application of a Hilbert transform. During this work, we computed those new attribute sections by using the standard time migrated seismic lines as input. Furthermore, we increased their interpretability also through the Fig. 1 - Attribute analysis on the Seismic line NOR3 (Acquasanta and Mt. dei Fiori area): a) standard amplitude section; b) Energy attribute calculated on NOR3; c) Pseudo-Relief in grey scale computed on NOR3.