Phase transitions of CH4 hydrates in mud-bearing sediments with oceanic laminar distribution: Mechanical response and stabilization-type evolution

• Published in: Fuel (Guildford) 2025-01, Vol.380, p.133185, Article 133185
• Main Authors: Gan, Bicheng, Li, Zhandong, Huo, Weixin, Zhang, Yuezhou, Li, Zhong, Fan, Ruibin, Zhang, Haixiang, Xu, Yanqing, He, YuFa
• Format: Article
• Language: English
• Subjects: Depressurization mining; Mechanical response; Natural gas hydrate reservoir; Reservoir stability; Reservoir subsidence
• ISSN: 0016-2361
• DOI: 10.1016/j.fuel.2024.133185

•The saturation and distribution pattern of hydrates affect the strength of shallow hydrate layers in deep water.•The content of sandstone is positively correlated with the displacement of reservoir during depressurization mining.•Horizontal wells are selected for short-term mining, and vertical wells are selected for long-term mining. Natural gas hydrates, abundant in deep-water shallow clay-bearing sediments, hold significant development potential. However, the impact of methane hydrate phase transition during depressurization on sediment mechanical properties remains unclear. Research focusing on shallow hydrate reservoirs in the South China Sea conducted mechanical response experiments on mudstone and sandstone sediments under layered distribution. A reservoir stability model for hydrate depressurization mining was established, considering varying reservoir physical conditions and mining methods. The study analyzed deposition and displacement patterns during mining and proposed strategies for both short-term trial and long-term mining under limited conditions. Findings indicate that depressurization mining reduces reservoir mechanical strength, with small elastic deformation initially and larger plastic deformation later. Failure strength of sediments increases linearly with hydrate saturation, and higher clay content increases settlement displacement and speed, reducing stability. Compared to vertical wells, horizontal wells result in smaller displacement amplitudes and more concentrated areas during initial development stages. However, the advantage of horizontal wells diminishes during long-term exploitation, making vertical wells more suitable for sustained methane hydrate development. This experiment uncovers failure mechanisms, underscores risks of subsidence and displacement, and offers valuable insights for safe mining.