Abstract

A suite of air gun configurations was tested in the Gulf of Mexico using a MEMS based OBC acquisition system. One advantage of this acquisition system was the significantly improved low frequency response of the sensors and instrumentation. The improved low frequency response allowed the response of the air gun configurations to be characterized to 1 Hz and below.

The data from the various air gun configurations were analyzed by comparative analysis between the air gun configurations, by analyzing the phase coherence within each of the tested configurations and by examining low-passed versions of brute stacks. The results from the three methods appear to support one another with the conclusion being that conventional air gun sources generate recoverable energy above 5 or 6 Hz. In the area where the test was conducted, coherent energy from the air gun sources could be identified at 11 to 12 s TWT for frequencies above 6 Hz.

Introduction

Low frequency (<10 Hz) content is very important for imaging deep targets and for inversion. Lack of low frequency content means that deep reflectors are poorly imaged or not imaged at all. Additionally other sources of information must augment the seismic data to stabilize inversions. Traditionally streamer data has limited frequency content below 10 Hz and is quite often deficient in frequency content below 5 Hz.

A suite of tests were conducted in the Gulf of Mexico to characterize the low frequency content of conventional air gun arrays and to investigate changes to traditional air gun technology to usefully modify the air gun signature.

The test utilized a 4C, MEMS based, cabled node style OBC acquisition system. Four 6-km acquisition cables were used for the data acquisition. Three of the cables were placed end to end to provide a 720 station, 2D line. The fourth cable was offset 100 m to the southwest of the third cable, Figure 1.

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