Marine vertical cable seismic (VCS) collects seismic waves by hydrophone array vertically suspended in seawater to prospect the offshore geological structure and monitor the reservoir. Due to its irregular source-receiver geometry, the primary imaging has narrow illustration coverage. Here, we proposed a cross-correlation transformation based on ghost wave interferometry. This method can transform the ghost reflections from the vertical cable seismic profile into the virtual surface seismic primaries just like those excited by the source and recorded by marine seismic towed-streamer below sea surface. After processing these virtual primaries with conventional method, we can obtain the ghost reflection imaging section with high resolution which effectively extend the illustration footprints in the subsurface. By application of this transform, virtual primaries are generated from the first-order ghost reflections of the actual VCS data. Then, migration of these virtual primaries provides a high-resolution image of hydrate-bearing sediments.

Offshore seismic surveys are typically conducted using streamers, which can make it challenging to accurately image deep and steep reflectors due to their horizontal layout and limited offset range. In recent years, vertical cable seismic acquisition has been developed as an alternative approach that utilizes a vertical layout to obtain wave field information not achievable by conventional streamers. However, relying solely on vertical cable seismic data does not produce high‐quality images due to its sparse detector distribution. To address this issue, we propose a joint imaging method based on reverse‐time migration that incorporates both streamer and vertical cable records. Our approach combines the back‐propagated wave fields of the streamer and vertical cable at each step of wave field extrapolation, providing more comprehensive wave field information than either one could provide individually. We then utilize zero‐delay cross‐correlation imaging conditions to generate a migration profile. To improve the efficiency of our reverse‐time migration algorithm, we employ a plane‐wave source encoding strategy for joint imaging. The effectiveness of our proposed method is validated using both the wedge model and the Marmousi model. By utilizing reverse‐time migration in the plane‐wave domain, our joint imaging method overcomes the limitations of poor imaging of steep‐dip formations with conventional streamer data. Additionally, it suppresses migration noise caused by insufficient illumination range from either streamer or vertical cable data alone. Overall, our joint imaging approach offers a promising solution for improving the accuracy and quality of offshore seismic surveys.

Amplitude Versus Offset forward modelling plays a crucial role in identifying gas hydrate reservoirs. However, since gas hydrates commonly exist in thin intermediate seafloor layers, traditional Amplitude Versus Offset techniques based on the Zoeppritz equation with the semi‐infinite medium assumption may not accurately depict the reflection amplitude of hydrates. In this paper, multi‐component Amplitude Versus Offset forward modelling using the Brekhovskikh equation was performed to simulate the Amplitude Versus Offset response of thin‐layered gas hydrate reservoirs more accurately. The numerical experiments demonstrate that the overall trends of the P‐wave and S‐wave Amplitude Versus Offset curves calculated by the Brekhovskikh equation and the Zoeppritz equation are consistent under various reservoir thicknesses, porosities and hydrate saturations, but the Amplitude Versus Offset curves calculated by the Brekhovskikh equation reveal more details. When the angle is greater than 30°, the gradient of the P‐wave Amplitude Versus Offset curve calculated from the Brekhovskikh equation as a function of hydrate saturation and porosity is greater than that calculated by the Zoeppritz equation, whereas the S‐wave Amplitude Versus Offset is not sensitive to changes in hydrate reservoir parameters. To further validate the Brekhovskikh equation in practical Amplitude Versus Offset analysis of gas hydrates, a geological model of gas hydrates is established based on logging data in the South China Sea. Subsequently, the bottom simulation reflection Amplitude Versus Offset of the P‐wave was computed using the Brekhovskikh equation and the Zoeppritz equation. Comparison with the actual vertical cable seismic data indicates that the Amplitude Versus Offset curve using Brekhovskikh equation is more consistent with the amplitude trend than the Zoeppritz equation. This finding suggests that the Brekhovskikh equation holds great potential for establishing an Amplitude Versus Offset identification marker for gas hydrates and improving seismic data interpretation in gas hydrate exploration.