Zander, Timo, Choi, Jung Chan, Vanneste, Maarten, Berndt, Christian , Dannowski, Anke , Carlton, Brian and Bialas, Jörg (2018) Potential impacts of gas hydrate exploitation on slope stability in the Danube deep-sea fan, Black Sea. Marine and Petroleum Geology, 92 . pp. 1056-1068. DOI 10.1016/j.marpetgeo.2017.08.010.

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Abstract

Highlights

• 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.

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.

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