Potential impacts of gas hydrate exploitation on slope stability in the Danube deep-sea fan, Black Sea

• Published in: Marine and petroleum geology Vol. 92; pp. 1056 - 1068
• Main Authors: Zander, Timo, Choi, Jung Chan, Vanneste, Maarten, Berndt, Christian, Dannowski, Anke, Carlton, Brian, Bialas, Joerg
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2018
• Subjects: Black Sea; Gas hydrate production; Gas hydrates; Geohazard assessment; Slope stability; Slope stability; Gas hydrates; Geohazard assessment; Black Sea; Gas hydrate production
• ISSN: 0264-8172; 1873-4073
• DOI: 10.1016/j.marpetgeo.2017.08.010

Methane production from gas hydrate reservoirs is only economically viable for hydrate reservoirs in permeable sediments. The most suitable known prospect in European waters is the paleo Danube deep-sea fan in the Bulgarian exclusive economic zone in the Black Sea where a gas hydrate reservoir is found 60 m below the seafloor in water depths of about 1500 m. To investigate the hazards associated with gas production-induced slope failures we carried out a slope stability analysis for this area. Screening of the area based on multibeam bathymetry data shows that the area is overall stable with some critical slopes at the inner levees of the paleo channels. Hydrate production using the depressurization method will increase the effective stresses in the reservoir beyond pre-consolidation stress, which results in sediment compaction and seafloor subsidence. The modeling results show that subsidence would locally be in the order of up to 0.4 m, but it remains confined to the immediate vicinity above the production site. Our simulations show that the Factor of Safety against slope failure (1.27) is not affected by the production process, and it is more likely that a landslide is triggered by an earthquake than by production itself. If a landslide were to happen, the mobilized sediments on the most likely failure plane could generate a landslide that would hit the production site with velocities of up to 10 m s−1. This case study shows that even in the case of production from very shallow gas hydrate reservoirs the threat of naturally occurring slope failures may be greater than that of hydrate production itself and has to be considered carefully in hazard assessments. •The Danube deep-sea fan offers best conditions for hydrate production.•Gas production out of a hypothetical methane hydrate reservoir was simulated.•Hazard assessment to investigate the hazard of production-induced slope failures.•Factor of Safety against slope failure is not affected by the production process.•Mobilized mass could hit the production site if landslide were to happen.