Mechanical properties of the clayey-silty sediment-natural gas hydrate mixed system

Abstract

Mechanical properties of hydrate-bearing strata are crucial to evaluate hydrate production related geohazards. However, the mechanical parameters of the hydrate reservoirs in the Shenhu area of the South China Sea have been rarely reported. In this paper, the sediments from the top of the hydrate reservoirs in the Shenhu area are taken to analyze the triaxial shearing behaviors of clayey-silty sediments containing tetrahydrofuran (THF) hydrates. The results indicate that the stress–strain curves of THF hydrate-bearing clayey-silty sediments show strain-hardening failure characteristics under a relatively low hydrate mass fraction (≤16.7%). Triaxial shearing strength, tangent modulus, and cohesion force increase with the increase of hydrate less fraction. However, prime results from pure THF hydrates reveal a brittle failure mode, which is totally different from that when hydrate mass fraction is more than 16.7%. Therefore, hydrate fraction (either mass fraction or volume fraction), rather than hydrate saturation, is strongly recommended to characterize the content of hydrate within clayey-silty sediments. The clayey-silty sediment-hydratemixed system is suggested to be divided into pure sediment, hydrate-bearing sediment (HBS), sediment-bearing hydrate (SBH), and pure hydrate, for which a universally applicable mechanical property evaluation method is thus established.

Keywords

• Natural gas hydrate (NGH)
• Mechanical properties
• Clayey-silty sediment
• Shenhu area
• Tetrahydrofuran (THF)
• Mass fraction