Numerical Analysis of Soil Deformation and Collapse Due to Hydrate Decomposition

Abstract

Natural gas hydrates are an ideal alternative clean energy source. Many countries are currently attempting the trial production of gas hydrates. Japan became the first country to achieve offshore hydrate trial production in 2013, and China conducted 60 days of continuous trial exploitation in 2017. This study analyzes the changes in the internal stress of the hydrate zone and hydrate saturation of the soil throughout the monitoring period and calculates the failure stress of the hydrate deposit layer. The Mohr−Coulomb model is used to simulate Japan's test exploitation conditions to verify the feasibility of the method. Finally, the hydrate decomposition range, the difference in the soil dip angle in the test exploitation area, and the bearing capacity of the hydrate reservoir are numerically simulated to evaluate the stability of the soil. Through the sensitivity analysis of the hydrate decomposition range and the inclination angle of the hydrate sediment layer, it can be found that the hydrate decomposition range has the greatest impact on the deformation, and the soil around the decomposition area may be sheared and collapsed. Within 1 week of decompression and exploitation, the hydrate decomposition radius is approximately 3 m. When the inclination angle increases from 3°to 9°, the sediment deformation increases by 12 times. Therefore, it is necessary to pay attention to the critical value of the decomposition range during the exploitation process.

Experimental investigation on hydrate dissociation in near-wellbore region caused by invasion of drilling fluid: ultrasonic measurement and analysis

“…Nevertheless, some issues will probably occur during drilling or exploitation of natural gas hydrates offshore (Yan et al 2018;Song et al 2019;Yan et al 2020;Yang et al 2021;Li et al 2021a). Among them, as presented in Figure 1, hydrate dissociation around wellbore and borehole collapse caused by drilling uid disturbance during drilling operation is one issue that can't be ignored (Li et al 2020).…”

Review on the Test Methods and Devices for Mechanical Properties of Hydrate-Bearing Sediments

“…Dissociation of hydrates leads to a decrease in effective stress due to the release of methane gas and water [10], triggering the risk of geohazards such as seabed subsidence, wellbore failure, and large-scale submarine landslide collapse [11][12][13][14][15]. Furthermore, the safety of drilling platforms is seriously affected by the creep of the reservoir [16][17][18]. Therefore, the mechanical properties obtained from the reservoir are of great importance in forecasting the potential risk of geological hazards [19].…”

Hydrate Dissociation Evaluation and Stratum Subsidence Response Induced by Depressurization in Hydrate-Bearing Permafrost

“…In particular, a few studies investigated the relationship between hydrate decomposition front and reservoir settlement. Hydrate decomposition is the critical factor leading to reservoir subsidence, 34 so it is essential to study the relationship between hydrate dissociation front and reservoir subsidence. By establishing the relationship between them, we can predict the stratum subsidence in advance according to the hydrate decomposition front and set the safe hydrate dissociation range according to the formation subsidence limit.…”