Claude Signer

Three‐dimensional texture attributes for seismic data analysis

In this paper we describe several new 3D texture attributes for automated interpretation of seismic data. The attributes, dip, azimuth, chaotic texture, and continuity, are robust with respect to properties such as tilted layers and amplitude variations. They are applicable to mapping of for example gas chimneys, structural features such as fault systems and salt domes and stratigraphic features such as carbonate reefs, sand channels, and fan systems.

Seismic reservoir monitoring on Gullfaks

Until recently, time‐lapse seismic monitoring was considered unproven for tracking the movement of an oil‐water contact (OWC). However, Statoil petrophysicists working on sonic logs from the Gullfaks Field in the Norwegian North Sea uncovered changes in log response that were favorable for seismic monitoring. Open hole logs from three wells drilled through the original OWC, compared to logs from wells drilled into water‐flushed areas, showed consistently higher velocities in the water‐filled zones than in those filled with oil.

Joint inversion of PP and PS reflection data for VTI media: A North Sea case study

Despite the significant advantages of combining PP and PS reflection data in anisotropic parameter estimation, application of this approach has been hindered by the inherent complexity of PS‐wave moveout. To overcome this problem, V. Grechka and I. Tsvankin suggested a model‐independent procedure to construct the traveltimes of pure SS‐wave reflections from PP and PS data. Here, we apply their method and anisotropic multicomponent stacking‐velocity tomography to a 2‐D line acquired over the lower Tertiary Siri reservoir in the North Sea.The computed traveltimes of SS reflections from several horizons are used to estimate the effective SS‐wave normal‐moveout (NMO) velocities, which are combined with the NMO velocities of PP‐waves in the tomographic velocity analysis. Comparison of the vertical and NMO velocities of the PP‐ and SS‐waves provides clear evidence of anisotropy in the section above the reservoir. The interval parameter estimation is performed under the assumption that the section is composed of...

Anisotropic inversion and imaging of PP and PS reflection data in the North Sea

The technology of ocean-bottom surveys has put mode-converted waves at the forefront of seismic exploration and reservoir characterization. For example, PS-waves proved effective in imaging offshore reservoirs screened by gas clouds that cause high attenuation/scattering of compressional energy (e.g., Thomsen, 1999). Also, information about shear-wave velocities contained in converted modes can be used to separate the effects of saturation and pressure and reduce uncertainty in predicting lithology and fluid saturation. The high sensitivity of PS-wave reflection coefficients to shear-wave velocity and density makes converted-wave AVO analysis potentially powerful for detecting hydrocarbon-saturated rocks.

Reservoir characterisation using 4C seismic and calibrated 3D AVO

In this case study, modern seismic technology is used to characterise the Lower Tertiary Sin reservoir (Norwegian-Danish North Sea border). Based on 4-component (4C) seismic and calibrated 3D AVO (Amplitude Versus Offset) data, it is possible to define fluid types, assess reservoir quality and map the geometry of the trap. It is well-known that the ratio of P wave velocity and S wave velocity (V p /V s ) in porous media is sensitive to both lithology and type of pore fluids. As a consequence. both these effects influence the AVO response. Whereas extensive well-log information is usually required to calibrate the lithology effect if AVO analysis is to be use for mapping of pore fluids, this paper presents a procedure for using seabed 4C seismic profiles to calibrate the lithology effect and thereby enables pore-fluid mapping from 3D AVO. Such a methodology is attractive at the exploration or appraisal stage when the well control is limited. The potential of the procedure is demonstrated in a case study of a Late Paleocene fan system from the North Sea. Firstly, 3D spectral attributes are used to divide the seismic data into depositional packages. Then the 4C seabed data are processed using a novel model-based technique. The model consistency obtained between all data sets allows a calibration of the 3D AVO cubes to be computed. Finally, the calibrated 3D AVO cubes can be inverted for fluids in each lithological unit recognised.