Natural Gas Hydrates
Whether the triggering of a phase-change from hydrates to gas and water – during gas production – by depressurization/thermal-stimulation/chemical-inhibitor-injection - would significantly deteriorate - the strength and stiffness of Hydrate-Bearing Sediments and alter the stress field – and thereby, leading to wellbore-stability/sand-production/marine-subsidence/landslides issues?
If so, which one of the following four parameters would remain to be the most sensitive – in mitigating the cohesion force of Hydrate-Bearing Sediments – leaving aside the variations in internal friction angle?
(a) hydrate-dissociation time;
(b) residual hydrate saturation;
(c) hydrate dissociation ratio;
(d) initial hydrate saturation?
In addition, upon the enhancement in hydrate dissociation ratio, to what extent, the mechanical behavior of Hydrate-Bearing Sediments are expected to vary – during the evolution of the volumetric strain – towards evaluating it’s dilatancy characteristics?
The geomechanical behavior of hydrate sediments depends on the hydrate saturation at a particular time. If we are looking at the subsidence/landslides / wellbore-stability issues, the hydrate dissociation rate is very important (from the geomechanics point of view). There are some constitutive models which are able to predict the behavior of hydrate sediment under different hydrate saturation. These models are the MHMC model (Karl et al., 2010), the MHCS model (Uchida et al., 2012 and 2016), the HISS-MH model (Gai et al., 2017), and the Hydrate CASM model (De La Fuente et al., 2020). The Critical state models are able to predict the more realistic volumetric response of hydrate sediments.
Recently, we have performed a numerical study for the elastic model and the HISS-MH for solving the boundary value problem; and it was observed that near the well-bore with the HISS-MH model, 15% of volumetric strain is reached as compared to 8% for elastic model (after 30 days) under same initial conditions.
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