Acoustic field characteristics of seismic surveys in the shallow water environment of the Bohai Sea

Abstract

AbstractAir gun arrays are designed to generate strong energy pulses of less than 100 Hz for offshore oil and gas exploration. In shallow seas, due to the directivity of air gun arrays, the complex propagation conditions and the limitations of acquisition methods, it is difficult to accurately evaluate the spatial time and frequency transmission characteristics of airguns. To alleviate the existing lack of knowledge about the transmission characteristics of air gun pulses in the shallow waters of the Bohai Sea, we analysed three‐dimensional ocean bottom cable seismic data collected during a seismic survey in the Bohai Sea, China, in June 2017, which were used to evaluate the reception level, frequency domain characteristics and spatial distribution characteristics within a 5.55 × 5.575 km area. The results showed that in shallow water, multipath propagation causes downfrequency chirplike sounds and an increased sound field. Within 0.3 km, the transmission model follows a cylindrical diffusion, and the sound loss rate decreases as the transmission distance increases until reaching 8 km. Signal capture by the sound channel results in a high transmission loss frequency band, whereas multimode interference weakens the transmission loss. The gun array directivity and the transmission channel are the two main factors affecting the acoustic field. This research provides an improved understanding of the acoustic field of airguns in the Bohai Sea, which can benefit the acoustic modelling of air gun arrays, the design of future seismic exploration projects and the conservation of marine life.