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3D/4C Emilio

Azimuth processing and anisotropy analysis in a fractured carbonate reservoir

Eni E&P, San Donato, Italy

James Gaiser

WesternGeco, Denver, Colorado, U.S.

Andrea Grandi

Polimi, Milan, Italy

Heloise Lynn

Lynn Inc., Houston, Texas, U.S.

Corresponding author: laura.vetri@agip.it

The first 20% of the full text of this article appears below.

In recent years multicomponent 3D seismic data have demonstrated their usefulness for characterizing fractured reservoirs. Many theoretical and field studies have shown that variation of attributes (such as velocity, amplitude, and frequency of P-wave data acquired along different source to receiver paths), can be used as an indicator of azimuthal anisotropy. Lateral heterogeneity encountered by the different azimuth source-receiver raypaths could give rise to azimuthal variations in traveltime and/or transmission characteristics, and thus masquerade as azimuthal anisotropy. To remove this ambiguity, mode-converted split shear waves can be employed. S-wave splitting across a fractured medium is a well studied and understood phenomenon that exploits the traveltime delay between the fast and the slow S-waves, and their polarization azimuths to infer fracture properties.

In analyzing the anisotropy effects at a target, the presence of an anisotropic overburden must be taken into account. The presence of both dipping fractures and fracture systems of different orientation can complicate the simple model used by current theory, where fractures are assumed to be vertical and parallel.

To test the suitability of state-of-the-art multicomponent seismic technologies for fracture characterization and to identify the fracture system in the carbonate reservoir, a 3D/4C survey was recorded at Emilio Field in the Adriatic Sea. Four PP-wave and eight PS-wave restricted azimuth data sets, suitable to detect azimuthal anisotropy, were produced by exploiting the 320 CMP fold coverage and the uniform azimuth distribution. The PS-wave azimuth volumes were combined together through 4C Alford rotation for the final fracture analysis. Valuable anisotropy information was derived from pre-and poststack analysis of all these volumes.

This paper presents highlights of the azimuthal data processing and the results of anisotropy analyses. Indications from seismic data were crosschecked with fracture information from the geologic setting, borehole data, and well production in the investigated area.

Emilio Field . . . [Full Text of this Article]