Reducing seismic reflector distortion beneath gas clouds in the Malay Basin using full-wavefield imaging approaches

Abstract

A seismic example from the Malay Basin is presented, demonstrating improved seismic imaging beneath gas clouds using full-wavefield imaging approaches. Overall imaging concepts, synthetic examples, and field implementation strategies are discussed, and results that tie with well information are presented. Seismic imaging beneath gas clouds using the full-wavefield redatuming technique improves the image by estimating the waveform transmission operators via equivalent-medium representation of the overburden from the gas cloud reflection response for use in a form of multidimensional deconvolution of the wavefield. The other example shown uses the full-wavefield migration seismic imaging technique, which utilizes primaries and higher-order multiples as signals to improve the reflectivity estimation in imaging. The demonstrated full-wavefield imaging approach uses information carried by the gas cloud reflection response to correct seismic image distortion. Removing the internal multiple using conventional demultiple processing in the gas cloud area will also remove the valuable information of the subsurface that it carries. Such multiples must be preserved for this method to be successful. The information is translated into transmission operators that are estimated by simulating the reflection response through an effective medium of the gas cloud overburden. The effective medium is obtained via nonlinear full-waveform inversion techniques from the reflections of the gas cloud overburden area. Finally, a deconvolutional process removes the transmission operators from the gas cloud reflections and recovers the underlying reflectors. Full-wavefield imaging can reconstruct the amplitudes of the reflection response below a gas cloud overburden zone so that the complex transmission imprint on the area underneath is removed properly. The Malay Basin field case study shows that implementation of this approach can provide a reliable amplitude image of the subsurface affected by gas clouds, calibrated and verified by the well information.