Abstract
Hydrate decomposition is an important potential cause of marine geological disasters. It is of great significance to understand the dynamic relationship between hydrate reservoir system and the overlying seabed damage caused by its decomposition. The purpose of this study is to understand the instability and destruction mechanisms of a hydrated seabed using physical simulations and to discuss the effects of different geological conditions on seabed stability. By applying pressurized gas to the low permeability silt layer, the excess pore pressure caused by the decomposition of hydrate is simulated and the physical appearance process of the overlying seabed damage is monitored. According to the test results, two conclusions were drawn in this study: (1) Under the action of excess pore pressure caused by hydrate decomposition, typical phenomena of overlying seabed damage include pockmark deformation and shear–slip failure. In shallower or steeper strata, shear-slip failure occurs in the slope. The existence of initial crack in the stratum is the main trigger cause. In thicker formations or gentler slopes, the surface of the seabed has a collapse deformation feature. The occurrence of cracks in the deep soil layer is the main failure mechanism. (2) It was determined that the thickness and slope of the seabed, among other factors, affect the type and extent of seabed damage.
Highlights
Gas hydrates are special ice-like compounds; its stability is affected by temperature and pressure [1].the pressure of the stable zone decreases or temperature rises, leading to hydrate dissociation [2].Thermal disturbances to a hydrate stratum during hydrate exploitation or natural environmental changes may cause dissociation of the hydrate
It can be seen from the table that the destruction of the overlying seabed caused by hydrate decomposition simulated in this paper can be divided into two failure modes
The failure modes of models 20-5, 20-10, 20-15 and 13-5 are annular collapse failure
Summary
Gas hydrates are special ice-like compounds; its stability is affected by temperature and pressure [1].the pressure of the stable zone decreases or temperature rises (caused by activities such as earthquakes, volcanoes, climate change, or a drop in sea level), leading to hydrate dissociation [2].Thermal disturbances to a hydrate stratum during hydrate exploitation or natural environmental changes may cause dissociation of the hydrate. The pressure of the stable zone decreases or temperature rises (caused by activities such as earthquakes, volcanoes, climate change, or a drop in sea level), leading to hydrate dissociation [2]. The dissociation of the hydrate releases 164 times the volume of gas and 0.8 times the volume of water into the pore space [3]. This compound is a natural source of clean energy and a potential factor that induces geological hazards [4]. Hydrate decomposition and submarine landslides are related, and hydrates may be an important reason for associated submarine landslides [5,6,7]. Despite the observations of ongoing and previous studies, the mechanism of hydrate decomposition in slope sediments is still unclear and requires further investigation
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