Study On The Influence Of The Seabed Structures Stability Due To Natural Gas Hydrate Dissociation

With the comprehensive and rapid development of economy, energy demand is growing quickly. The oil and gas resources are hugely consumed. And the development of economy faces enormous challenges. The gas hydrate is considered to be the most development prospects of alternative energy in the21st century. However, when environmental conditions change, the stability of gas hydrate bearing sediments is damaged and large amounts of gas and water are released, which greatly reduces the engineering mechanical properties of seabed sediments. The softening of the seabed soil, slope failure and submarine landslides geological disasters will occur, and thus causing the destruction of the seabed engineering facilities, such as seabed pipelines, communication cables, drilling platforms.Therefore, it is very necessary to research stabilities of the seabed structures due to hydrate dissociation. In this paper, finite element numerical simulation is used to study the influences of seabed structures due to hydrate dissociation. The main works could be summarized as follows:(1) To study the process of hydrate sediments modulus softening and strength reduction, the finite element numerical method is established to consider the hydrate dissociation using stress release method. The corresponding computer program is developed and the reliability of the program is discussed.(2) The program is used to simulate the influences of submarine slope stability due to hydrate dissociation. Three calculation conditions are designed to study the effects of modulus softening and strength reduction on slope deformation respectively. Then, the effects of overlying soil thickness on the slope stability and deformation in the process of hydrate dissociation are discussed.(3)Then, laying the foundation in hydrate sediments is simulated. When pile foundation is located in the strata at different depths, two different conditions of pile end in the hydrate layer and the lower sediment layers are compared. The effects of pile foundation and the surrounding soil stress and deformation due to hydrate dissociation are analyzed.Finally, when pile foundation is at different distances from the hydrate layer, the effect of hydrate dissociation on the pile foundation is researched. Four calculation conditions of10m,50m,70m and80m spacing are designed. When how far the pile foundation and hydrate layer, there is the minimal impact in the stress and deformation of the pile foundation due to the hydrate dissociation, which provides a reference for the development of gas hydrate in the seabed pile foundation stability.