Abstract

The earthquake poses a potential hazard to the safety of deep-sea gas hydrate reservoir. The increase in temperature of ocean induced by global warming causes the decomposition of some deep-sea natural gas hydrates, which intensified the adverse effects on deep-sea reservoir. By revising the dynamic theory of natural gas hydrate porous media, a simplified model of vertical seismic response of deep-sea gas hydrate reservoir was established. The analytical solution of vertical seismic response of natural gas hydrate reservoir is obtained by Laplace transform method. The effects of water depth, temperature and saturation on vertical seismic response of natural gas hydrate reservoirs are studied in detail. Due to the decomposition of natural gas hydrate, the reservoir contains gas bubbles, and the bulk compressive modulus of the reservoir fluid changes under deep water pressure, which has significant impact on the vertical seismic response.

Introduction

Natural gas hydrates (NGH) have become an important part of the world's energy development because of their cleanliness, efficiency, and abundance of reserves. However, natural gas hydrates are known to be unstable and the greenhouse effect of their gas generation is much higher than that of carbon dioxide, which can cause serious ecological disasters if they are not disposed of properly. With the increase of climate warming in recent years, the melting of polar ice caps and the warming of seawater, these factors have affected the stability of deep-sea natural gas hydrate reservoirs and have caused the decomposition of some deep-sea natural gas hydrates (Archer et al., 2009; Yan et al., 2020). Due to this decomposition, natural gas hydrate in the reservoir no longer exists in its original solid form, but produces some bubbles to melt in the pore water, forming pore water containing micro-bubbles, which moves with pore water. When seismic waves are transmitted to the quasi-saturated reservoir after partial hydrate decomposition, its seismic effect often causes seismic amplification effect in the reservoir, so the seismic response study of natural gas hydrate is an important work with application value.

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