Geophysical data acquisition - OGS

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Seismic inversion Coordinator: Aldo VESNAVER The Cat3D tomographic software G. BÖHM M. PERONIO The software package Cat3D allows the 3D traveltime inversion by adaptive irregular grids, for arbitrary recording geometry and combinations of different wave types: direct, reflected, refracted and diffracted arrivals. Since it allows, for example, the joint inversion of surface and VSP data, it is a valuable tool for calibrating the seismic surveys with the well information. During the year 2000, the software commercialization was supported by the OGS partners: Paneura (Trieste, Italy) and Fact (Houston, USA). Paneura had a booth at the EAGE International Conference and Exhibition in Glasgow. Various copies of Cat3D were installed in Europe. A major improvement of the software efficiency was an aggressive use of the dynamic memory allocation, which allowed increasing the computational speed, the size of processed data and the model complexity. Several graphic features were improved during the year, and new Import/Export model formats Surfer ® and GeoQuest ® , which were added to the existing ones (GoCad ® and Jason Geosystems ® ). The software installation was made easier and its documentation significantly extended. A particular effort was spent for the software porting for all major Linux distributions (Slackware, Red Hat, Mandrake, Caldera, Debian) in low-cost personal computers; of course, the Cat3D package runs also in different hardware platforms (as IBM, Sun and SGI) under the Unix operating system. Furthermore, we added a user-friendly menu for defining grids with a circular symmetry, which we prepared and tested for 3D VSP’s. Cover image of the user manual for the tomographic Cat3D package. 33
Joint 3D inversion of P, S and converted waves A. VESNAVER G. ROSSI During the last few years, ocean-bottom cables (OBC) were used at a large scale for 3D marine surveys for recording the three components of the particle velocity and the pressure waves. Also on land surface surveys and in VSP’s this technology is expanding, since it allows detect and separate P, S and converted waves. P and S velocity and, in particular, their ratio, are important lithological parameters to reconstruct porosity and pore pressure in the rocks. This information is important to delineate boundaries and preferential migration paths both in hydrocarbon reservoirs and in shallow water-saturated rocks. In most cases, rock interfaces reflect both P and S waves, and convert part of their energy from one wave type into the other one. When these events are observable and can be reliably picked, we can enhance a lot the 3D lithological description of the Earth, because of the data redundancy with respect to the estimated parameters. In fact, the unknowns describing the interfaces do not increase, and those ones for the velocities just double; viceversa, if P, S, P-S and S-P waves are available, including both reflected and head waves, the traveltime data increase by a factor much larger than two. Thus, the Earth model is much better constrained by the experimental data, and more robust with respect to errors in the traveltimes. The joint inversion of P, S and converted waves has an additional advantage. The sought velocity fields of P and S waves are almost decoupled, when considering pure P and S arrivals: their only connection are the possible common reflecting interfaces in the Earth. Converted waves provide new equations in the tomography inversion, which directly relates the two velocity fields. We set up a software prototype for the elastic inversion by generalizing our previous acoustic code. The ray tracing algorithm is based on the Fermat’s principle, and determines the ray path for a given ray signature by a bending type approach. For example, in a P-S converted wave, we use the P velocities up to the conversion point, where we switch to the S field, for computing and minimizing the traveltime along the ray path. The P and S velocities are estimated by an ART, SIRT or weighted SIRT algorithm. Time-lapse 3D tomography A. VESNAVER F. ACCAINO G. DAL MORO G. MADRUSSANI G. ROSSI The response in a seismic survey over a producing hydrocarbon reservoir changes during the years, due to the different pressure conditions of gas and the movements of the gas/oil/water interfaces. This information is crucial for optimizing the hydrocarbon production, locating the new wells in the unswept areas, and where the hydraulic conductivity is expected to be adequate, as in fractured or permeable formations. The 4D-TAIL Project is aimed at detecting these variations of lithologic parameters by Amplitude Versus Offset (AVO) analysis and 3D tomographic imaging. The OGS partners are two oil companies, i.e. TotalFinaElf UK and Norsk Hydro, and the University of Milan. This project is supported by the European Union in the Thermie Programme. 34
Page 2 and 3: Istituto Nazionale di Oceanografia
Page 4: Contents Introduction . . . . . . .
Page 7 and 8: Sea, close to the Antarctic Peninsu
Page 10 and 11: Measurements while drilling (data a
Page 12 and 13: Vallazza research well: 3D-RVSP sei
Page 14 and 15: Therefore, having beside a high ele
Page 16 and 17: • Standard 20’ container modifi
Page 18 and 19: • Offshore gravimetric survey “
Page 20 and 21: The GPR instruments. Integrated met
Page 22 and 23: Seismic data processing Coordinator
Page 24 and 25: allow for the different spatial sam
Page 26 and 27: Results of application of the stati
Page 28 and 29: Measurements while drilling (R & D)
Page 30 and 31: Wave modeling Coordinator: Géza SE
Page 32 and 33: Phase velocities of the five wave m
Page 34 and 35: (SPEM) and the Wavenumber Integrati
Page 36 and 37: The Marche Microzonation Project is
Page 40 and 41: The joint inversion of direct, refl
Page 42 and 43: Transferring technology from the oi
Page 44 and 45: At the end of the year, we started
Page 46 and 47: ODP Leg 178 - Site Location Site 10
Page 48 and 49: Core 1165B-14H Composite diagram sh
Page 50 and 51: Cenozoic Evolution of the South Ork
Page 52 and 53: Magallanes-Fagnano master fault TWT
Page 54 and 55: (Top): Structural map of the BSRs o
Page 56 and 57: Physical properties of sediment cor
Page 58 and 59: Bathymetric map of the North Atlant
Page 60 and 61: Synthetic Aperture Radar (SAR) remo
Page 62 and 63: Publications Wave modeling ARNTSEN,
Page 64 and 65: Seismic inversion ROSSI, G., AND VE
Page 66 and 67: TINIVELLA, U. AND LODOLO, E., 2000.
Page 68 and 69: POLETTO, F., LOVO, M., AND CARCIONE
Page 70 and 71: REBESCO, M., CITA, M.B., HIEKE, W.,
Page 72 and 73: Visitors Peter F. BARKER, British A
Page 74 and 75: About Trieste, Italy Overwiew Tries
Page 76 and 77: Near Trieste One cannot miss a visi

Geophysical data acquisition - OGS

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