Tomographic imaging by reflected and refracted arrivals at the North Sea

Abstract

We discuss some processing steps of a marine 3-D data set from the Oseberg field, North Sea. We compare the prestack depth‐migrated images obtained by the velocity fields provided by different tools: velocity spectra, reflection tomography, and joint tomographic inversion of reflected and refracted arrivals. The last ones are definitely better. We also produced a synthetic example by modeling the estimated earth structure and the actual recording geometry, and we reached similar conclusions. The correlation between reflected and refracted signals may be unclear for later arrivals because of their reciprocal interference and multiple reflections. We adopt a technique based on a surgical mute in the τ-p domain, which allows coupling the signals coming from the same elastic interface.

Joint 3D inversion of SWD and surface seismic data1

“…These important aspects are not described here for brevity. However, we got encouraging results by this approach in these further applications: we refer the interested reader to other recent papers (Vesnaver et al . 1999, 2000).…”

Characterization of the shallow aquifers by high‐resolution seismic data

“…Figure 7 shows a few picked reflections in a common shot gather, where we notice a good lateral continuity of the signal. The adopted tomographic method (Vesnaver et al 1999) is based on the simultaneous iterative reconstruction procedure algorithm (Van der Sluis and Van der Vorst 1987; Stewart 1991) and the minimum‐time ray tracing (Böhm et al 1999). We estimated the velocity field and the reflector structure in sequence, from the shallowest to the deepest horizon.…”

“…The AVO analysis was performed in order to extract the Poisson's ratio contrast (Accaino et al 2005), which provides useful information to characterize the petrophysical properties of the shallow layers, such as the fluid content. Finally, we used the interval velocity fields obtained from the travel‐time tomographic inversion (Vesnaver et al 1999) to perform a 2D pre‐stack depth migration of the processed seismic data, in order to build a realistic depth section of the investigated area.…”

Attenuation tomography: An application to gas‐hydrate and free‐gas detection

“…This provides information on both velocity and attenuation for the same seismic events and, therefore, on the rock formations crossed by the rays considered. We use the method described in detail by Vesnaver et al (1999) for both velocity and attenuation inversion. It uses a modified version of the minimum-time ray-tracing method developed by Böhm et al (1999) and an iterative process for the inversion, based on the simultaneous iterative reconstruction technique (SIRT) algorithm (van der Sluis and van der Vorst 1987).…”