Casing-sediment interaction during gas hydrate dissociation : constitutive and centrifuge modelling

• Main Author: Baghbanrezvan, Sina
• Other Authors: Ng, Charles Wang Wai
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: Energy harvesting; Energy conversion; Centrifugation; Natural gas; Hydrates; Sedimentation and deposition; Mechanical properties; Methane hydrate
• Online Access: https://repository.hkust.edu.hk/ir/Record/1783.1-128175; https://doi.org/10.14711/thesis-991012994405203412; https://repository.hkust.edu.hk/ir/bitstream/1783.1-128175/1/th_redirect.html

Gas hydrate-bearing sediments (GHBS) have been considered as a potential energy source for the future due to their global abundance. While hydrate significantly strengthens the host sediment, dissociation would inevitably alter hydro-mechanical properties of it. Consequently, this could trigger instabilities in the gas production casing. It is, therefore, essential to devise safe and economical strategies for energy harvesting from GHBS at commercial scale. The understanding of these inter-related causes and mechanisms is still very limited. In this study, a state-dependent critical state model is developed for methane hydrate-bearing sediments (MHBS) within the theoretical framework of bounding surface plasticity. A phase parameter is newly introduced into the constitutive model to account for the coupled effects of temperature and pore pressure on the mechanical behaviour of MHBS. This unique feature of the proposed model enables it to capture the behaviour of MHBS inside the methane hydrate stability region. A non-associated flow rule is adopted and a modified dilatancy expression is proposed considering the degree of hydrate saturation, morphology, phase parameter and stress state of MHBS. The comparison between the computed results and measured results of drained triaxial tests on MHBS reveals that the model is capable of capturing the key features such as the evident strain softening behaviour due to hydrate degradation and the change in stress-strain and volumetric behaviour of MHBS at different initial conditions inside the stability region. A key contribution of this study is a newly developed centrifuge energy harvesting chamber (CEHC). This is the first chamber that can operate at elevated gravities with the capability of sustaining the thermodynamically favourable conditions for gas hydrate formation, sustaining a continuous inflow of high-pressure water at the boundaries during dissociation, and an in-flight control of wellbore pressure and surcharge loading. Centrifuge modelling can recreate the ...