Multistage Triaxial Tests on Laboratory‐Formed Methane Hydrate‐Bearing Sediments

Abstract

A sound understanding of the geomechanical behavior of hydrate-bearing sediments (HBSs) is essential not only for assessing reservoir and wellbore stability during methane gas production but also for projecting the impact of global warming on the stability of geological settings that contain hydrates. This study experimentally investigated the geomechanical responses of laboratory-formed methane-HBS to triaxial shearing under drained conditions. The hydrate pore habit formed in the sediments is noncontact-cementing, which is different from contact-cementing or grain-coating hydrate pore habits formed when the excessive gas method is used. The multistage triaxial test method, which shears a single specimen under different confinements, was employed to examine its applicability in measuring geomechanical properties of the HBS. Conventional single-stage triaxial tests were also performed to serve as baselines. The results show that both the strength and stiffness of HBS increase with increased hydrate saturation and confining stress. Shear dilatancy increases with increased hydrate saturation and decreased confining stress. The peak strength and peak/postpeak shear dilation measured using the multistage tests are comparable to those using the single-stage tests. However, the stiffness measured in later stress stages in the multistage tests was enhanced by the stress-strain history of earlier stages. Therefore, the multistage test offers an efficient way of measuring the strength and volumetric response of the HBS with a much smaller number of specimens than the single-stage test. This benefits the geomechanical characterization of the HBS, as obtaining the pressure cores is extremely costly and preparing lab samples is usually sophisticated and time consuming. Key Points: • Multistage triaxial tests are conducted on noncontact-cementing, hydrate-bearing sediments under drained conditions • The strength, dilatancy, and stiffness of the hydrate-bearing sediments are measured • The multistage test can be a viable and efficient method to measure the strength and dilatancy of the hydrate-bearing sediments

Strain Rate‐Dependent Hardening‐Softening Characteristics of Gas Hydrate‐Bearing Sediments

“…The analysis of stress-strain behavior based on Rowe's stress-dilatancy theory suggests that GHs contribute a structuration effect in GHBS. This effect was substantial in water-limited systems with structuration strength (c′) up to 2 MPa at the onset of dilation and 1.6 MPa at peak strength (Figure 6b and supporting information Table S3), which was high compared to results from other experimental studies with GHBS (e.g., Choi et al, 2018;Ghiassian & Grozic, 2013;Yoneda et al, 2016). However, in water-saturated specimen c′ was substantially lower, reaching values of 0.4 MPa at the onset of dilation and 0.6 MPa at peak strength.…”

Pore‐Scale Investigation Of Methane Hydrate‐Bearing Sediments Under Triaxial Condition

“…However, understanding interactions between hydrate and sediment skeleton within the hydrate bearing sediment has been dominantly supported via simplified conceptual models (Waite et al, 2009;Yun et al, 2007). Limited published triaxial tests are mostly on sediments with hydrate saturations lower than 70% when methane is used as guest molecule (Choi et al, 2018;Hyodo, Li, et al, 2013;Yoneda et al, 2016). Meanwhile, high hydrate saturations, sometimes higher than 80%, are often found in natural reservoirs (Boswell et al, 2009;Kumar et al, 2014;Lee et al, 2013;Wu et al, 2011;Yamamoto & Ruppel, 2015), and these high energy density reservoirs are the first targets for gas production.…”

Micromechanical Investigation of Stress Relaxation in Gas Hydrate-Bearing Sediments Due to Sand Production

“…MH has attracted research interest in a range of engineering and scientific fields, among which are geophysical exploration [14][15][16][17]; environmental impact [7,18,19]; geohazards (e.g., slope stability, dissociation-induced tsunami events, deep-water mud volcanoes) [20][21][22][23]; mechanical property evaluation [24][25][26][27][28]; macro-and micro-mechanical constitutive modeling [29][30][31][32][33][34][35]; thermo-hydro-chemical-mechanical (THCM) formulations for simulation of gas production and the associated difficulties [36][37][38][39][40][41][42][43][44][45][46][47].…”