Schlumberger

Technical Paper: 3D VSP acquisition and 3C processing on a deep subsalt prospect in the Gulf of Mexico

Society: SEG
Paper Number: 3064038
Presentation Date: 2008
 

Abstract

Good quality seismic images can be difficult to achieve in the deepwater, sub-salt sediments of the Gulf of Mexico. 3D vertical seismic profiles (3D VSP), with the receivers placed below the salt, can be a useful technique in improving sub-salt image quality. This paper describes how a 3D VSP was used to prove the existence of reservoir horizons, confirm reservoir dip and generally confirm seismic correlations. Success was achieved by way of several innovations in acquisition and processing. We deployed 40 downhole receivers, the largest array deployed in the Gulf of Mexico at the time of recording. Previously, a survey of this magnitude required several tool settings and several times the rig time. Noise in the data prompted development of station consistent deconvolution, a new casing ringing reduction technique. We also adapted surface seismic techniques for reducing random noise and source noise from a nearby surface seismic shoot. Common image point gathers (CIP) were introduced as a means of verifying the migration velocity model and as quality control tool for the final image stacking. The 3D VSP image volume produced an excellent tie to the existing surface seismic and well data, and confirmed presurvey interpretations and correlations.