Processing of Three Dimension Vertical Cable Data over SEG/EAGE Physical Model
Authors: Guimaraes M.G. , Sekharan K.K. , Sukup D. , Krail P. 
Published: October 2008

A physical model similar to the SEGIEAGE numerical salt model was constructed to study the problems and issues of acquiring and processing seismic data over geological situations involving salt and subsalt layers. A large 3D dataset acquired simulating vertical cable is composed of 8 swaths with 8 cables with 8 transducers in each cable to produce truly 3D Common Cable Gathers (CCG) that were processed through pre-stack depth migration. The final image is composed of the stack of all CCG migrated including both upcoming and down-going wave fields. Partial images obtained from stack of depth volumes of each field separately show that down-going field data had reflections with more continuity and higher SIN ratio than the up-coming waves in parts with non-steep dips. The up-coming, however, did a better job in the flanks of the salt. Separation of the up-coming and downgoing fields to different datasets for separated migration did not result much difference in the final image. The general results have been showing that vertical cable technique is an excellent tool to obtain depth image of complex geologic structures. The power of stacking migrated images of different hydrophones and cables with different illuminations increase tremendously the signal-to-noise ratio of the depth image resulting In a more reliable information of the subsurface.

Introduction

Imaging geological structures beneath salt is still a great challenge and even the most current conventional acquisition equipment and sophisticated processing techniques used to obtain the Image of these structures fails to provide reliable results. In order to understand the issues involved in acquiring and processing seismic data over such areas, a physical model Similar to SEG/EAGE numerical model (I) was constructed (funded by Marathon Oil Co and Louisiana Land and Exploration) at the Allied Geophysical Laboratories of the University of Houston (2). The model consisted of a complex salt block with a canopy, toe faults and rugose surface at the top, surrounded by sedimentary layers and a three dimensional structure beneath the salt. A conventional 3D marine data set consisting of nearly 20 million traces was acquired over this model. A different approach to conventional 3D data acquisition was used. Vertical cables anchored at the bottom of the ocean while a source boat shot a regular grid over the surveyed area (3) were simulated. This technique of seismic data acquisition has been seen as an excellent method for exploration of different types of prospects, (4), (5), (6) and (7) especially for deep water and areas where the conventional streamer is unable to obtain coverage. We simulated this different approach to acquire data over the SEGIEAEG physical model. The model and a detailed acquisition scheme description were presented last year (8). In this paper we will show the procedures used in processing the data through pre-stack depth migration and present the results.

Acquisition

The data were acquired in the beginning of 1997. Basically 8 cables were deployed in each of four areas of the model. In each area, two shot patches displaced by 25 m in both × and y direction of 99 lines and 165 shots spaced at 50 m apart, were carried out (fig. 1).