How can we reduce the environmental impact of marine seismic surveys?

Marine seismic sources emit acoustic energy in the form of the seismic wavefield used for the remote sensing of subsurface impedance contrasts in the earth. The environmental impact of seismic sources is typically measured in terms of impulsive acoustic pressure (the sound pressure level, SPL) and the accumulated acoustic energy (the sound exposure level, SEL). We use global examples of the following marine source concepts to quantify the relative SPL and SEL in each scenario: • Large arrays of air guns activated simultaneously with no significant overlap in emitted acoustic pressure, • Small arrays of air guns activated simultaneously or in rapid succession with overlap in emitted acoustic pressure, • Individual air guns activated continuously with overlap in emitted acoustic pressure, and • Towed marine vibrators operated continuously. Continuous sources clearly have the lowest SPL and SEL. Examples from various basin settings are shown where benefits in data quality and survey efficiency may also complement the lower environmental impact. Another surprising geophysical outcome is that continuous sources with low SPL do not have compromised signal penetration to deep target depths compared to traditional large arrays of air guns activated simultaneously. These outcomes are relevant to how future marine seismic surveys might be designed to meet stricter environmental controls as well as presenting various new opportunities for how the surveys could be acquired more efficiently and processed.