Abstract
Laboratory-synthesized specimens are employed for an experimental study on the mechanical properties of hydrate-bearing sediments (HBS) due to the difficulty of field coring. A representative synthesized sample for the analysis of the mechanical properties of HBS in the experimental study requires evenly distributed hydrates in the pores of the sample. However, a specimen made with an improper sand–water mixing method might have an uneven water distribution, resulting in an uneven hydrate distribution when applying the ice-seeding method for hydrate formation. This study adopted three kinds of methods to mix sand and water before forming hydrates and applied the low-field nuclear magnetic resonance (NMR) technique to investigate how these methods affect the hydrate distribution, further affecting the mechanical properties. To analyze the mechanical properties of HBS, we conducted drained triaxial tests. As shown in low-field NMR, when we compacted a sample of the sand–water mixture and froze it upside-down before hydrate formation, a sample with an even water distribution was obtained. Subsequently, the hydrate in HBS distributed also evenly. The stress-strain curves present different strain softening and hardening patterns due to the different hydrate distributions. Moreover, the samples with the evenly distributed hydrates have higher initial elastic modulus and strength than the ones made with other methods.
Highlights
Accepted: 25 April 2021Natural gas hydrate, a crystalline material composed of a water cage surrounding natural gas molecules [1,2], exists widely in deep permafrost and submarine strata where there are the proper temperatures and pressures, as well as abundant natural gas [3,4]
It is of vital importance to study the mechanical properties of hydrate-bearing sediments (HBS) for the efficiency and safety of natural gas hydrate production
The distribution of hydrates may be affected by the distribution of water in the sample before hydrate formation, which can be obtained by low-field nuclear magnetic resonance (NMR)
Summary
A crystalline material composed of a water cage surrounding natural gas molecules [1,2], exists widely in deep permafrost and submarine strata where there are the proper temperatures and pressures, as well as abundant natural gas [3,4]. Commercial exploitation of natural gas hydrate has not been achieved, and it is still in the research stage, due to the safety problem of exploitation and gas transportation [7,8]. The decomposition of hydrate will destroy the original cemented structure of the reservoir, which may prompt strata instability and even climate change [13,14]. It is of vital importance to study the mechanical properties of hydrate-bearing sediments (HBS) for the efficiency and safety of natural gas hydrate production
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
