Modelling the thermo-hydro-mechanical behaviour of marine methane hydrate-bearing sediments

• Main Author: De La Fuente Ruiz, Maria
• Format: Thesis
• Language: English
• Published: University of Southampton 2020
• Subjects: Methane hydrate
• Online Access: https://eprints.soton.ac.uk/437857/; https://eprints.soton.ac.uk/437857/1/De_La_Fuente_Maria_PhD_Thesis_Jan_2020.pdf

This three-paper format thesis is divided into the following scientific topics; geomechanical investigation of methane hydrate-bearing sediments (MHBS), fully coupled thermohydro-mechanical (THM) modelling of their behaviour during hydrate dissociation and prediction of hydrate saturation in pores inhibited by capillary pressure. The occurrence of hydrates in pores increases the sediment strength, stiffness and dilatancy and favours its mechanical stability. However, hydrate dissociation may compromise its structural integrity and cause failure. To assess the risk of occurrence of hydrate-related geohazards or geotechnical issues it is imperative to ascertain the factors controlling the mechanical behaviour of gas hydrate reservoirs. The first part of this thesis develops a new mechanical model for MHBS. The Hydrate-CASM model attributes the stress-strain changes observed in MHBS to variations in the host sediment available void ratio, isotropic yield stress and swelling line slope due to hydrate formation and dissociation. In particular, the model assumes that the decrease of the available void ratio of the host sediment during hydrate formation stiffens its structure and has a similar mechanical effect that the increase of the sediment density. The Hydrate-CASM model is successfully applied to published experimental tests that cover a wide range of hydrate saturation, several hydrate morphologies and confinement stress. The results capture the main features observed in the mechanical behaviour of synthetic MHBS and provide novel insights into understanding the role of hydrate saturation at governing the mechanical properties of the sediment. MHBS are characterized by highly interdependent physical processes, including mechanical deformation, fluid flow, thermal flow and phase change reactions. Reliable simulations of their behaviour require efficient mathematical models capable of capturing the aforementioned interdependencies in a coupled manner. The second part of this thesis develops a fully coupled THM formulation ...