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SWLGS Luncheon Topics

Updated January 20, 2004

May 2002

Imaging through gas clouds: A case history from the Gulf of Mexico
Steve Knapp and Nigel Payne, Seitel Data and Tony Johns, WesternGeco


Abstract Summary
Results from the world's largest 3D four component OBC seismic survey will be presented. Located in the West Cameron area, offshore Gulf of Mexico, the survey operation totaled over 1000 square kilometers and covered more than 46 OCS blocks. The area contains numerous gas invaded zones and shallow gas anomalies that disturb the image on conventional 3D seismic, which only records compressional data. Converted shear wave data allows images to be obtained that are unobstructed by the gas and/or fluids. This reduces the risk for interpretation and subsequent appraisal and development drilling in complex areas which are clearly petroleum rich. In addition, rock properties can be uniquely determined from the compressional and shear data, allowing for improved reservoir characterization and lithologic prediction.

Data acquisition and processing of multicomponent 3D datasets involves both similarities and differences when compared to conventional techniques. Processing for the compressional data is the same as for a conventional OBC survey, however, asymmetric raypaths for the converted waves and the resultant effects on fold-offset-azimuth distribution, binning and velocity determination require radically different processing methodologies. These issues together with methods for determining the optimal parameters of the Vp/Vs ratio (?) will be discussed. Finally, images from both the compressional (P and Z components summed) and converted shear waves will be shown to illuminate details that were not present on previous 3D datasets.

Biographical Sketch
Steve Knapp (stknapp@seitel-inc.com) manages 4SIGHT, an alliance between Seitel Data and WesternGeco formed to acquire, process and market 3D multicomponent data in the shallow Gulf of Mexico. He began his career with Digicon Geophysical after obtaining a Bachelor's degree in Geology and Materials Science from Rice University and a Master degree in Geology from Texas A&M. Following assignments in the Netherlands and Colombia with Digicon, he joined Triton Energy as an international explorationist, coordinating seismic data acquisition and processing on many projects covering the globe. In 1999 he joined Seitel Data and has been involved in the advancement of emerging technologies such as AVO, inversion, visualization in addition to multicomponent seismology..