Physical Properties of Gas Hydrate-Bearing Pressure Core Sediments in the South China Sea

Jiangong Wei,Tingting Wu,Xiuli Feng,Jinqiang Liang,Wenjing Li,Gang Wu,Rui Xie,Paolo Madonia

doi:10.1155/2021/6636125

Abstract

Gas hydrates are a potential future energy resource and are widely distributed in marine sediments and permafrost areas. The physical properties and mechanical behavior of gas hydrate-bearing sediments are of great significance to seafloor stability and platform safety. In 2013, a large number of pressure cores were recovered during China’s second gas hydrate drilling expedition in the South China Sea. In this study, we determined the gas hydrate distribution, saturation, physical properties, and mechanical behavior of the gas hydrate-bearing sediments by conducting Multi-Sensor Core Logger measurements and triaxial and permeability tests. Disseminated gas hydrates, gas hydrate veins, and gas hydrate slabs were observed in the sediments. The gas hydrate distribution and saturation are spatially heterogeneous, with gas hydrate saturations of 0%–55.3%. The peak deviatoric stress of the gas hydrate-bearing sediments is 0.14–1.62 MPa under a 0.15–2.3 MPa effective confining stress. The permeability is 0.006– 0.095 × 10 − 3 μ m 2 , and it decreases with increasing gas hydrate saturation and burial depth.

Highlights

Natural gas hydrates, which are widely distributed in continental margins and permafrost areas, have been suggested to be a potential renewable energy resource in the future
By comparing our results with those of previous studies, we investigated the influences of the gas hydrate distribution, saturation, effective confining strength, and burial depth on the permeability and strength of the sediments
The physical properties of the hydrate-bearing pressure core sediments recovered during the GMGS2 in the South China Sea were analyzed and reported for the first time

Summary

Introduction

Natural gas hydrates, which are widely distributed in continental margins and permafrost areas, have been suggested to be a potential renewable energy resource in the future. Previous lab tests and numerical simulations have revealed that gas hydrate formation and decomposition may change the sediments’ properties, such as their permeability and strength [10,11,12,13,14,15]. Lab experiments are the main method used to determine the physical properties of gas hydrate-bearing sediments, such as their permeability and shear strength. Key parameters, such as the permeability and shear strength, needed for numerical simulations can be obtained through lab experiments and field testing [18]. In order to prevent gas hydrates from dissociating during core retrieval from marine sediments [23, 25, 26], various pressure coring tools have been developed in recent years [3, 27,28,29]; only a few studies have been conducted on pressure core gas hydrate-bearing sediments [22, 23, 30]

Methods

Discussion

Conclusion