Marine Broadband Airgun Vibration Source Based on Combination of Virtual and Real Depth

Abstract

The invention discloses an offshore broadband air gun seismic source based on virtual and real depth combination. The source comprises a main seismic source and N-stage auxiliary seismic sources, wherein a first wave of the first-stage auxiliary seismic source in the N-stage auxiliary seismic sources and a ghost wave of the main seismic source are completely counteracted at the far-field end, a first wave of the next-stage auxiliary seismic source and a ghost wave of the previous-stage auxiliary seismic source are completely counteracted at the far-field end, the auxiliary seismic sources areequivalent to air gun seismic sources set at a specific virtual depth, meanwhile, the main seismic source and the N-stage auxiliary seismic sources are designed to be air gun arrays with real depth combination, and first waves of air guns at different depths in the main seismic source are subjected to same-phase superposition by adopting a time-delay excited mode. According to the method, the low-frequency response is effectively improved, meanwhile, the frequency domain notch introduced by the virtual and real depth ghost waves is compensated, so that the design purpose of a broadband seismicsource wavelet is achieved.

Description

technical field [0001] The invention belongs to the field of airgun seismic source design, in particular to a marine broadband airgun seismic source based on the combination of virtual and real depths. Background technique [0002] At present, the commonly used air gun seismic source at sea is composed of multiple air guns with different capacities at the same depth. Simultaneous excitation of multiple guns is used to achieve the superposition of the first wave in phase, and at the same time, the difference in the bubble oscillation period caused by the difference in capacity is used to offset the remaining bubbles. When the first wave propagates to the sea surface, the polarity reverses to form a ghost wave. The existence of source ghosts causes the absence of some specific frequencies in the frequency domain and reduces the resolution of seismic data, which is called the notch effect. In order to eliminate the notch effect, it is proposed to place airgun sub-arrays or si...

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