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The Leading Edge; January 2005; v. 24; no. 1; p. 86-92; DOI: 10.1190/1.1859708
© 2005 Society of Exploration Geophysicists
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Hybrid inversion techniques used to derive key elastic parameters

A case study from the Nile Delta

R. Roberts, J. Bedingfield and D. Phelps

Apache Egypt Companies, Cairo, Egypt

A. Lau

Apache Corp., Houston, USA

B. Godfrey, S. Volterrani, F. Engelmark and K. Hughes

WesternGeco, Cairo, Egypt

Corresponding author: Ron.Roberts@egy.apachecorp.com

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

This case study reviews the workflow and the results achieved in terms of updated development drilling plans from a 1500-km2 prestack inversion project over a West Mediterranean Deep Marine Concession in the Nile Delta. Four successful exploration and one appraisal well have been drilled to date on this concession. Figure 1 shows the location of the concession (red box) in the offshore Nile Delta, and indicates the locations and field names of the discoveries to date. The 3D survey over this concession was recorded using long offsets (6000 m). Information contained in these offsets has been used to try and obtain rock property estimates that may help distinguish lithology and fluid types in order to high grade drilling locations and help build more reliable reservoir models.


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  		Figure 1. West Mediterranean Concession outlined by the red box. The four prospects/discoveries targeted by the project are shown.

 
The main inversion objective was to improve the existing reservoir model to help create an optimum development plan for the gas-charged complex of channel and levee sands discovered in the block. This was enabled by the generation of 3D cubes of three elastic parameters: P-impedance, Poisson's ratio, and density. These data were then used to derive additional 3D cubes of petrophysical parameters such as water saturation and net-to-gross.

Successful seismic inversion requires a high signal-to-noise ratio and a wide bandwidth. In this case study, a hybrid inversion technique was used to derive the seismic attributes. The technique combines full waveform prestack inversion and three-term AVO inversion. The project was focused only on the Pliocene interval where gas-charged type 3 AVO sands are present; it was not considered reliable for the Miocene and below where the sands are deposited below a high-velocity anhydrite layer. To date, the Pliocene has been an amplitude-supported play in the area (Figure . . . [Full Text of this Article]






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