<p>The experimental and numerical investigation of THCM process coupling is important to better understand reservoir geotechnical behavior and sub-surface processes. In particular, when THCM process coupling is dominated by focused fluid migration and localized chemical or microbiological reactions, bulk sediment and, thus, reservoir geotechnical behavior becomes poorly predictable. To improve the understanding of these complicated processes and process coupling on relevant time and spatial scales, it is necessary to combine experimental and numerical simulation approaches, and to develop complementary investigation strategies.    </p><p>We use different high-pressure flow-through experimental systems with triaxial testing units in combination with tomographical imaging tools (e.g. X-ray CT and ERT) to simulate and analyze relevant processes in ocean and earth systems. Our geotechnical studies are carried out at high hydrostatic pressures up to 40 MPa and temperatures between -30°C and 80°C. The experimental systems allow testing of large sample specimen (up to a diameter of 150 mm and a height of 400 mm). In particular, we investigate scenarios with heterogeneous phase distributions and dynamic flow conditions, which cannot be interpreted based on the assumption of homogeneous phase distributions in a sensible manner.</p><p>Here, we focus on discussing experimental and numerical strategies and problems towards understanding geotechnical behavior of heterogeneous sediments, including issues from gas migration in fine-grained sediments (e.g. silty clays), gas hydrate formation under two-phase flow conditions, and localized failure and shear banding in cemented soils. We present results from recent studies on underground usage including gas production and injection scenarios, which are relevant for the understanding of reservoir behavior, storage scenarios and, overall, marine sediment and slope stability. One of the most important aspects is to improve current strategies for combined and complementary experimental and numerical studies, considering that the overall objective is to understand processes on a reservoir scale.</p>