Abstract:

GI air gun is becoming the main shooting source in offshore seismic exploration. With two gas chamber, named chamber G and chamber I, it can suppress bubble oscillation much better than conventional air gun with only one gas chamber. Based on free bubble oscillation theory, the working mechanism of GI air gun is analyzed, and the numerical model of GI air gun signature is established considering the effects, such as heat transfer across the bubble wall and fluid viscosity, on bubble oscillation. The model is used to simulate the bubble oscillation and far-field signature,  and the simulation results indicate that: ① when the gas is released from chamber G and the bubble reaches its maximum volume, the released gas from chamber I restrains effectively the contraction of bubble, the movement of bubble wall is slowed down, and the bubble is gradually becoming stable. ② the signature of GI air gun has strong peak amplitude and weak sidelobes, which is helpful for high resolution offshore seismic exploration.

Key words: offshore exploration, signature, GI air gun, numerical simulation, heat transfer