海上地震勘探GI枪子波数值模拟

摘要

GI枪震源已经逐步成为海上地震勘探的主要激发方式.常规气枪只有一个腔室,而GI枪具有G腔和I腔2个腔室,能够较好地压制气泡振荡.基于自由气泡振动理论,分析GI枪的激发机制,在考虑气泡壁的热传导作用和流体粘度对气泡振动影响的基础上,建立了海上勘探GI枪子波数值模型,并对气泡的振动过程和远场地震子波进行了数值模拟.结果表明:当G腔内气体释放所形成的气泡体积达到最大时,I腔内气体的释放有效地抑制了气泡的收缩,气泡壁运动速度明显减小,气泡变得稳定;GI枪激发所产生的子波具有明显的峰值和较小的旁瓣,有利于高分辨率海上地震勘探.%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 Gl 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.