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

Abstract

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

Strain Rate‐Dependent Hardening‐Softening Characteristics of Gas Hydrate‐Bearing Sediments

“…Numerical GH reservoir simulators have been used to study the behavior of GHBS during gas production (Gupta et al, ; Rutqvist et al, ; Rutqvist et al, ) or in marine slope destabilization (Jiang, Sun, et al, ; Sultan & Garziglia, ; Zander et al, ), and there is strong effort to improve soil mechanical constitutive models and model couplings. A number of nonlinear elastic (Miyazaki, Aoki, et al, ; Yu et al, ) and elasto‐plastic (Klar et al, ; Lin et al, ; Sun et al, ; Uchida et al, ) constitutive models have been proposed.…”

Joint interpretation of geophysical field experiments in the danube deep-sea fan, Black Sea

“…1) were chosen as the basis for further studies aimed at seafloor drilling and deep sub-seafloor sampling, and to investigate the role of hydrates within the multiple slope failures observed along the Danube Fan (Bialas et al 2014). WA1 at around 1500 m water depth is characterized by strong amplitude events with reversed polarity (compared to the seafloor event; used throughout this paper) and variable lateral extent within the hydrate stability zone in the sediment filled paleo-canyon and levee structures (Zander et al 2017b;Zander et al 2018). At WA2, the BSR shoals upward towards the seafloor.…”

Gas migration pathways and slope failures in the Danube Fan, Black Sea

“…1. Mass transport deposits (MTDs), or slumps associated with slope failure events are characterised by hummocky, chaotic and irregular seismic facies, with discontinuous, low to high amplitude reflections (Popescu et al, 2004;Winguth et al, 2000;Zander et al, 2017a).…”