The impact of bubble curtains on seismic air-gun signatures and its high-frequency emission

Abstract

In marine seismic acquisition, air guns are the most common source and, in recent years, research on their impact on the marine environment has increased. The main focus is on the reduction of emitted high frequencies, approximately greater than 200 Hz, which are normally not useful for seismic imaging. Therefore, potential ways to reduce the high frequencies from air guns are investigated and the development of alternative source types has increased. We have investigated the impact of bubble curtains on the source signature from seismic air guns because bubble curtains are known to mitigate high frequencies in other applications, e.g., pile driving for offshore wind farms. We have conducted tank experiments with two different configurations of bubble curtains around a single air gun and compared the results to the conventional source signature without a bubble curtain. The two different bubble curtains vary in size and in the way they are attached to the air gun. The amount of injected air into the bubble curtains is varied for both configurations. We compare the measured results to simulated data using a common model for air-gun source signatures. The results indicate a reduced peak amplitude with increasing air injection through the bubble curtain. This corresponds to a gradually decreasing frequency content for frequencies greater than 50 Hz. The frequencies of the source signal of less than 50 Hz are practically unaffected by the bubble curtain. In addition, the bubble time period of the source signal is slightly increased with an increasing amount of air injection through the bubble curtain. The main cause for the reduced peak amplitude is likely to be a buffer effect of the bubble curtain on the released air. Hence, a bubble curtain concentrated around the air-gun ports could be an efficient and practical solution to reduce the high-frequency acoustic emission from air guns.