Description: Results from two recent field trials, onshore in the Alaska permafrost and in the Nankai Trough offshore Japan, suggest that natural gas could be produced from marine gas hydrate reservoirs at compatible yields and rates. However, both field trials were accompanied by different technical issues, the most striking problems resulting from un-predicted geomechanical behaviour, sediment destabilization and catastrophic sand production. So far, there is a lack of experimental data which could help to understand relevant mechanisms and triggers for potential soil failure in gas hydrate production, to guide model development for simulation of soil behaviour in large-scale production, and to identify processes which drive or, further, mitigate sand production. We use high-pressure flow-through systems in combination with different online and in situ monitoring tools (e.g. Raman microscopy, MRI) to simulate relevant gas hydrate production scenarios. Key components for soil mechanical studies are triaxial systems with ERT (Electric resistivity tomography) and high-resolution localstrain analysis. Sand production control and management is studied in a novel hollow-cylinder-type triaxial setup with a miniaturized borehole which allows fluid and particle transport at different fluid injection and flow conditions. We further apply a novel large-scale high-pressure flow-through triaxial test system equipped with μ-CT to evaluate soil failure modes and triggers relevant to gas hydrate production and slope stability. The presentation will emphasize an in-depth evaluation of our experimental approach, and it is our concern to discuss important issues of translating laboratory results to gas hydrate reservoirs in nature. We will present results from high-pressure flow-through experiments which are designed to systematically compare soil mechanical behaviour of gas hydrate-bearing sediments in relevant production scenarios focusing on depressurization and CO2 injection. Experimental datasets are analyzed based on numerical models which are able to simulate coupled process dynamics during gas hydrate formation and gas production.

Description: The understanding of thermo-hydro-chemo-mechanical coupling of dynamic processes, which occur in marine gas hydrate-bearing sediments during natural gas production or slope destabilization, is limited. Recent developments in geotechnical testing offer new approaches to closely simulate sub-marine in-situ conditions, and to generate benchmark tests for numerical model development. Especially when applied in combination with tomographic techniques (e.g. X-ray CT or ERT), high-pressure flow-through triaxial testing could answer important questions related to multi-scale effects, influence of spatial heterogeneities and process dynamics on the stress-strain behavior of gas hydrate-bearing sediments. Based on experimental studies on heterogeneous gas hydrate formation from two-phase fluid flow, we demonstrate the need for advanced mechanical testing. Further, we present the setup of advanced geotechnical test systems combined with X-ray CT or ERT analysis, as well as preliminary results from flow-through triaxial testing with the novel systems.