A state-dependent hypoplastic model for methane hydrate-bearing sands
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RESEARCH PAPER
A state-dependent hypoplastic model for methane hydrate-bearing sands Jun Liu1 • Shun Wang3 • Mingjing Jiang1,2 • Wei Wu3 Received: 18 November 2019 / Accepted: 12 September 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The mechanical behaviors of methane hydrate-bearing sands (MHBS) are largely affected by the presence of methane hydrate, temperature, and pore pressure. In this study, we present a simple hypoplastic model for MHBS. Methane hydrate saturation is included as a state parameter affecting the mechanical behaviors of MHBS. A new phase parameter is introduced to account for the coupled effects of temperature and pore pressure on the mechanical behaviors of MHBS. The phase parameter can be determined by a simple function of temperature and pore pressure. Comparison of the predictions with experiments shows that the model is able to capture the salient behaviors of MHBS. Keywords Critical state Hypoplastic constitutive model Methane hydrate Phase state Sands
1 Introduction Methane hydrate (MH) is a crystalline clathrate composed of methane and water molecules. It is widely distributed beneath permafrost and in marine continental margin sediments. MH can be used to extract methane gas and has attracted global interests as a promising energy resource [42]. According to field investigations, MHs primarily exist in the forms of discrete nodules or veins in fine-grained sediments or disseminate in the pore spaces of coarse sands. Compared to fine-grained sediments, sand reservoirs are more attractive for MH exploitation due to the high permeability of sand media and the high concentration of MHs [1, 37]. However, the exploitation of MH may destabilize methane hydrate-bearing sands (MHBS) and potentially lead to the unsteady deformation of seabed [56], & Mingjing Jiang [email protected] & Wei Wu [email protected] 1
Department of Civil Engineering, Tianjin University, Tianjin 300072, China
2
State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China
3
Institut fu¨r Geotechnik, Universita¨t fu¨r Bodenkultur Wien, Feistmantelstrasse 4, 1180 Vienna, Austria
in-stability of production well [31], and even marine landslides [26]. It is therefore crucial to properly characterize the mechanical behaviors of MHBS for MH exploitation. The mechanical behaviors of MHBS have been extensively investigated by laboratory tests. Sufficient experimental results [4, 5, 9, 11, 20, 24, 54] show that the stiffness, strength, and dilation of MHBS are enhanced by increasing MH saturation, which is defined as the ratio of MH volume to sediment pore volume. Besides, the mechanical behaviors of MHBS are markedly influenced by pore pressure and temperature [9, 11]. For example, within hydrate stability region, the peak strength of MHBS increases by 18% when temperature decreases from 10 to 1 C [11], and a 40% increase of the peak strength is observed when pore pressure increases
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