Geohazard Detection in Deepwater Clastics Basin: A Seismic Technique with Application to Deepwater Mediterranean

By

Nader C. Dutta¹, R. Utech¹, Tarek Nafie², John Bedingfield³

(1) WesternGeco, Houston, TX (2) WesternGeco, Cairo, Egypt (3) Apache Egypt Company, Maadi, Egypt

 Detection of hazardous zones, associated with high-pressured fluids in unconsolidated sands and shales, prior to drilling, is essential for environmental as well as health and safety. Drilling for deepwater targets is associated with high cost and risk, while margins of commercial operations are small. Therefore, it is imperative to control cost through accurate well planning and reliable anticipation of geohazards.

This paper deals with a novel seismic approach that uses the full bandwidth and the entire offset range of the conventional 3D seismic data to detect the presence of hazardous zones. Both in shallow and deeper zones, P- and S-velocities were determined using seismic full waveform prestack inversion. Shallow waterflow (SWF) layers in the deepwater, Mediterranean were identified through the associated high ratios of P- to S-velocities. A new, rock model-based approach especially suited for deepwater pore pressure imaging was applied to predict the presence of both shallow and deeper over-pressured zones.