55th EAEG Meeting

An algorithm for the elastic inversion in the w-k domain is considered. Diffraction tomographic techniques are used in the elastic case; 3D P-waves sources and vertical receivers are located on the surface of a medium characterized by small deviations of the elastic parameters from an uniform background. Born approximation is invoked and a singular value decomposition of the parameters - data transfer function is derived. Least square estimation along the eigenvectors is used to perform multiparameter inversion on synthetic data obtained in the space time domain. Numerical inaccuracies and interpolation errors can severely degrade the inversion of S impedance and density. P impedance, as usual, turns out to be well conditioned.

This paper presents some experimental results from a test line accquired by the Norwegian Petroleum Directorate in block 24/12 in the Norwegian part of the North Sea. This block is caracterized by, in general, poor seismic data quality. Reasons for the seismic quality problem is thought to be soft tertiary clays, some shallow gas-accumulations and the depth of some of the targets. Main targets have been jurassic and tertiary sands. In the Northern Barents Sea, the Norwegian Petroleum Directorate has for several years experienced that summing two parallell horizontally separated streamers give a noticeable signal to noice enhancement. This has also been experienced by HGS and Saga Petroleum as documented by Brink et. al. (1991). It was decided to shoot some profiles with this accquisition configuration in order to investigate if it could be helpful in this block, especially for the jurassic targets. As these targets are quite deep, it was decided to use two long streamers (4500 m). This enabled us to test both the effect of two streamers and the effect of different streamerlengths. The results of these tests will be presented in this paper.

The effects of irregular spatial sampling on prestack wave-equation processes such as DMO and migration have been noted by several authors for both 2-D and 3-D data. Phase and amplitude distortions arise as a result of applying DMO algorithms that assume regular spatial sampling to data not regularly sampled in offset, common midpoint (CMP), and azimuth. While algorithms now exist to compensate or equalize the DMO operator during data processing for such spatial irregularities, it is possible that random or systematic patterns in the data acquisition geometry leave deficiencies in the "DMO coverage" that cannot easily be remedied (Beasley and Klotz, 1992) . Traditional criteria for spatial sampling such as CMP fold and offset distribution are often set by rule of thumb and generally do not measure the quality of spatial sampling for DMO processing. In this paper, I demonstrate new methods of assessing the quality of data sampling for DMO that are based only on acquisition geometry and are independent of a geologic model or the actual seismic data.

Possible conflict between seismic surveys and commercial fishing has been a concern for the oil industry for many years. During the last 3 years, a significant research program on these problems have been undertaken in Norway, and the final results will be published during the spring of 1993. This paper will address the results of these research projects.

During recent years advances in software development has made it feasible to achieve decimeter accuracy in real-time in differential GPS (DGPS) systems on short ranges offshore under dynamic conditions. The technique applied is valled carrier phase ambiguity resolution on-the-fly (OTF). In May 1992 a test was performed on the seismic vessel New Venture of GEOTEAM Exploration Ltd A/S on a survey for Saga Petroleum a.s.

The resolution power of stratigraphic seismic inversion has been compared to a reservoir description based on 3D seismic attributes in a real case study of Rotliegend sandstones in the NW German gas province. The challenge of seismic interpretation in the study area consists of inter-well seismic reservoir prediction of thin sandstone reservoirs (thicknesses below 25 m) at depths between 4.5 and 5 km. Facies and diagenesis are the main limiting factors of prospects. A high degree of lateral heterogeneity has to be expected for several stacked reservoir zones. To unravel this complexity, 3D seismic has been used to a large extent (Burri et al. 1992). Some 3D wells are available to calibrate the seismic signature of different reservoir quality units.

Amoco's exploration team for the Kohat Plateau in the Northern Pakistan Foreland Region acquired and integrated a comprehensive data package which identified structures formed by oblique compression (transpression). Our data shows that basement is involved with the development of structures in this area and that each structure has very high vertical relief with thrust faults and reverse faults radiating outward. Our interpretation suggests that transpressional deformation resulted in forming en echelon tears which caused basement and the sediment cover to buckle to foren shishtarays (Pivnik & Sercombe, 1992), or structures which fit the 'Kohat Anticline Model' (Sercombe & etal, in prep.).

A large multichannel seismic reflection dataset, recorded along the pacific sector of the periantarctic shelf by the OGS-Trieste during the first geophysical surveys (1987-89) of the Italian Antarctic Reserch Program, has been processed and interpreted with specific techniques in order to draw a comprehensive scheme of the structure, the seismostratigraphy and the evolution of the Ross Sea. The exploration of this basin is of considerable scientific interest for reconstructing the main geodynamic phases which have produced the present crustal conditions of the Antarctic continent with particular regard to the following topics: - The uplift of the Transantarctic Mountains - The relationships between East and West Antarctica - The relationships between the rift processes along the pacific margin of Antarctica and the Gondwana breakup The present study illustrates methods and results of the processing and the interpretation of the antarctic seismic data with reference to the following research themes: - Reconstruction of the structural and seismostratigraphic characteristics of the sedimentary sequence - Outline of the deep crustal conditions in areas with favourable signal to norse ratio - Reconstruction of 3D structural models of the interpreted horizons - Preliminary time and space analysis of the deformation

Poui Field, Trinidad is an example of continued resource development and reserve growth through multi-discipline team efforts and technology application. The Field is structurally complex and extensively drilled requiring careful and detailed planning of development wells. The multi-discipline team perspective includes reservoir and operational engineering, geology, geophysics and computer mapping experts. Methods include delineation of complex structural fault blocks, field studies, reservoir management planning and 3-D seismic enhancements. Recoverable reserve estimates for Poui Field have grown from 68 million barrels of oil in 1973 to 226 million barrels of oil, presently.