Abstract

Natural gas hydrate (NGH) is a potential energy resource. To exploit this resource safely and sustainably, especially for long-term exploitation, it is necessary to investigate the time-dependent behavior of gas hydrate-bearing sediment. In this work, the influence of hydrate saturation and fines content on the shear rate dependence of hydrate-bearing sediments under plane strain conditions has been studied. The results show that the shear rate dependence of the hydrate-bearing sediments was more significant under a higher hydrate saturation. The fines content effection on the shear rate dependence was also discussed by the particle tracking velocimetry technology.

Introduction

Natural gas hydrate (NGH) is a clathrate crystal formed by gas (mainly methane gas) and water at low temperature and high pressure. It is widely found in deep seabed sediments and permafrost regions on land, and which is a promising energy resource (Wang et al., 2018). Most NGH resources exist in marine sediments, and the exploitation of them may cause geological and engineering-related problems, such as submarine ground and wellbore instability (Yoneda et al., 2011).

To realize the safe and sustainable exploitation of NGH resources, it is critical to study the mechanic characteristics of hydrate-bearing sediments. Especially, to ensure the possibility of long-term exploitation, research on the time-dependent behaviors of hydrate-bearing sediments is necessary. At present, only a small number of relevant studies under triaxial conditions have been reported (Iwai et al., 2018; Miyazaki et al., 2011), and it has been found that the hydrate-bearing sediments exhibit a significant time dependence. The geological characteristics in different regions are different, such as particle size distribution and hydrate saturation. And some geological disasters, such as submarine landslides, are plane strain (Alshibli and Sture, 2000). Therefore, it is necessary to study the time dependence of the mechanical characteristics of hydrate-bearing sediments with different hydrate saturation and fine particle content under plane strain conditions. Shear rate dependence study is an efficient method to investigate the time-dependent properties of materials. Previous studies (Wu et al., 2020) have found that under plane strain conditions, the stiffness and peak strength of hydrate-bearing sediments have significant shear rate dependence. With the same experimental equipment and research methods, more important related factors need to be studied.

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