Triaxial compressive properties of artificial methane-hydrate-bearing sediment

Abstract

[1] Knowledge of the mechanical properties of gas-hydrate-bearing sediments is essential for simulating the geomechanical response to gas extraction from a gas-hydrate reservoir. In this study, drained triaxial compression tests were conducted on artificial methane-hydrate-bearing sediment samples under hydrate-stable temperature-pressure conditions. Toyoura sand (average particle size: D 50 = 0.230 mm), number 7 silica sand (D 50 = 0.205 mm), and number 8 silica sand (D 50 = 0.130 mm) were used as the skeleton of each specimen. Axial loading was conducted at an axial strain rate of 0.1% min −1 at a constant temperature of 278 K. The cell and pore pressures were kept constant during axial loading. We found that the strength and stiffness of the hydrate-sand specimens increased with methane hydrate saturation and with the effective confining pressure, and the secant Poisson's ratio decreased with the effective confining pressure. The stiffness depends on the type of sand forming the skeleton of the specimens, although the strength has little dependence on the type of sand. According to an earlier work, hydrate-sand specimens are thought to contract in the early stage of axial loading before starting to expand owing to the dilatancy effect, as is the case for many other geological materials. The test results in this study are discussed in relation to the deformation mechanism proposed in an earlier work.

A Model for the Elastic Modulus of Hydrate-Bearing Sediments

“…The axial compression of Toyoura sandy sediments containing water and hydrate was conducted at drainage condition (Miyazaki et al, 2010(Miyazaki et al, , 2011. The initial porosity of the sand skeleton was 0.4.…”

Coupled multiphase fluid flow and wellbore stability analysis associated with gas production from oceanic hydrate-bearing sediments

“…The geomechanical properties of HBS were derived from laboratory experiments by Masui et al (2005Masui et al ( , 2008 and Miyazaki et al (2010Miyazaki et al ( , 2011 on reconstituted hydrate-bearing Toyoura sand as well natural offshore samples from Nankai Trough, Japan. We use a Mohr-Coulomb elastoplastic constitutive mechanical model in which the parameters describing the mechanical properties are corrected for pore-filling solid content (hydrate and ice).…”

“…We use a Mohr-Coulomb elastoplastic constitutive mechanical model in which the parameters describing the mechanical properties are corrected for pore-filling solid content (hydrate and ice). Based on the experimental results of Masui et al (2005Masui et al ( , 2008 and Miyazaki et al (2010Miyazaki et al ( , 2011, we assume that certain mechanical properties (bulk and shear moduli, and cohesion) increase linearly with hydrate saturation (Table 1). For example, from the data of Masui et al (2005Masui et al ( , 2008 we derived the cohesion values ranging from 0.5 MPa at 0% hydrate saturation to an extrapolated 2.0 MPa at 100% hydrate saturation; this results in a hydrate-dependent shear strength that matches the laboratory data quite well over relevant ranges of hydrate content ( Figure 1).…”

“…We assume that the dilation angle is independent of hydrate content, although the experimental results by Masui et al (2005Masui et al ( , 2008 indicate a slight increase in the dilation angle with hydrate content. The mechanical properties derived from Masui et al (2005Masui et al ( , 2008 and Miyazaki et al (2010Miyazaki et al ( , 2011 were chosen because of the lack of published geomechanical data on hydrate bearing…”

“…Gulf of Mexico sand, and because the data set of Masui et al (2005Masui et al ( , 2008 and Miyazaki et al (2010Miyazaki et al ( , 2011) is (to the author's knowledge) the most complete and systematic geomechanical strength data set of HBS available to date. Moreover, the geomechanical properties (strength and compressibility) of the Toyoura sand is consistent with typical deep water Gulf of Mexico unconsolidated sand of relatively high porosity (Zoback, 2007).…”