SEISMIC SIGNATURES OF LARGE AIR GUNS

Abstract

Large chamber air guns are a reliable and effective source of energy for marine seismic surveys. Air guns with chamber volumes of 300 and 1000 cubic inches demonstrate desirable low‐frequency responses and high absolute energy levels. Overall performance has been compromised, however, by the bubble effect. Previous attempts at minimizing the bubble response have resulted in loss of reliability, reduced power, or incomplete bubble suppression, or a combination thereof. In this paper, we present the results of experimental tests on air guns with 300 and 1000 cubic inch chambers and describe a divided‐chamber gun which greatly attenuates the bubble effect. Significant improvements in the width and flatness of the frequency spectra are demonstrated by analysis of the actual signatures obtained in deep water and with record sections comparing the results obtained with the standard and improved guns along an identical traverse. The bubble‐attenuating air gun simultaneously provides improved resolution, high absolute‐energy levels, and excellent reliability.