Scientific goals and objectives
Our high-pressure laboratories are used to investigate biogeochemical, geomechanical and geotechnical processes in marine sediments. The different experimental systems can be operated at high hydrostatic pressure (up to 40 MPa), a wide temperature range and under dynamic fluid flow conditions, which is necessary to simulate relevant deep-sea conditions and scenarios. Furthermore, the systems allow to apply and control mechanical loads and stresses to investigate sediment strength and stress-strain behavior under complex thermo-hydro-chemo-mechanical (THCM) process coupling. Process monitoring and analysis is based on using different online monitoring techniques and sensors (e.g. Raman and infrared gas sensors, local deformation and strain measurement, distributed in situ pressure-temperature sensors), and high-resolution imaging tools (e.g. X-ray CT and ERT).
The experimental systems are used for a large variety of research topics, including:
* Investigation of mechanisms and effects of formation, dissociation and conversion of gas hydrates in sediments
* Analysis of multiphase flow in sediments and rocks to characterize fluid migration at gas seeps or resulting from technical leakage
* Investigation of geotechnical risks of sediment destabilization and slope failure, and process development for sediment stabilization
* Simulation of transport-reaction processes in potential storage scenarios (e.g. CO2-fluid-sediment interactions and weathering reactions) and deep-sea mining
* Analysis of microbial processes in marine sediments (e.g. AOM and hydrocarbon degradation, microbial iron and manganese reduction, sulfate reduction and methanogenesis)
SYNCHRO-CT
In collaboration with APS GmbH Wille Geotechnik (Rosdorf, Germany), GEOMAR operates SYNCHRO-CT, a unique triaxial testing system with X-ray-CT. The testing system can be used for cylindrical sample specimen with a maximum height of 400 mm and a maximum diameter of 150 mm. The sample is mounted in an X-ray-transparent pressure vessel and tested using a 1000 kN load frame. Currently, the system is used for pore pressures up to 25 MPa. During the experiment, the μ-CT Scanner (150 kV X-ray source and high-resolution flat panel detector) is rotated around the fixed sample vessel. Sample scans can reach a resolution of 15 µm, depending on pressure vessel and sample sizes. The system allows visualizing heterogeneous phase distributions and structures, local processes and mechanical failure characteristics using reconstruction and segmentation workflows.
The high-pressure flow-through system NESSI allows investigating processes under similar conditions and constraints as in marine sediments. The system can be operated at maximum pressures of 35 MPa. Multi-purpose mixing vessels are used to prepare fluids with defined composition, which are transferred to the temperature-regulated pressure vessels using high-pressure piston pumps. Pressure, temperature and fluid composition can be monitored upstream and downstream from the sample using online sensors (e.g. Raman and IR gas sensors) or conventional sampling and analyses. This allows mass and volume balancing of relevant chemical and physical processes inside the vessel. NESSI can be flexibly operated with different pressure vessels (1L to 50 L; stainless steel, titanium or GFK) and in different configurations, which can be adapted to the specific research question. Among these configurations are NESSI-TRIAX, NESSI-ERT and NESSI-FLOW.
NESSI-TRIAX
NESSI-TRIAX
NESSI-TRIAX is a versatile setup for high-pressure flow-through experiments at defined mechanical stresses. It can be used for samples with a diameter of 80 mm and a maximum height of 400 mm, the standard sample height is 160 mm. The samples are mounted in a 40 L pressure vessel, which can also be adapted for other sample dimensions and holders. The temperature is regulated using a heat exchanger, which is mounted inside the pressure vessel. Axial loads are applied with a hydraulic piston in combination with an internal load frame. Fluids enter and leave the sample through filter plates. Fluid delivery, pore pressure regulation and load control is achieved with high-precision piston pumps. The system is equipped with axial and lateral strain sensors, and volumetric strain can also be measured using calibrated volume changes inside the pressure vessel and pore pressure pumps.
The operation and equipment of NESSI-TRIAX is very robust, thus it is well adapted for test series on sensitive sediments under complicated constraints. It is often used to carry out preliminary studies in preparation of more complicated studies with NESSI-ERT or SYNCHRO-CT.
NESSI-ERT
NESSI-ERT is a flexible high-pressure flow-through system which allows the analysis of large sediment samples (maximum diameter 150 mm, maximum height 400 mm). To facilitate mounting of large samples and multiple sensor systems, temperature regulation is achieved with a high-pressure cooling system, which continuously circulates cooling fluid at a defined confining pressure. Similar to NESSI-TRIAX, mechanical loads are applied with a hydraulic piston in combination with an internal load frame. The load frame is also used to house and position 24 magnetic-inductive deformation sensors, which are used to measure local strain behavior. NESSI-ERT is equipped with high-resolution electrical resistivity tomography (ERT, 96 electrodes in 8 planes) which enables analysis and visualization of phase distributions based on conductivity differences and contrasts. NESSI-ERT can further be equipped with a central well and lateral fluid injection ports to simulate complicated fluid flow scenarios and fluidization of sediment particles. Solid particles are collected in a solids separator at the bottom of the central well. The flexibility of NESSI-ERT and the complementary measurement devices makes it a good setup for analyzing heterogeneous phase distributions, focused fluid migration and mechanical effects from dynamic biogeochemical processes.
NESSI-ERT
NESSI-FLOW
NESSI-FLOW uses a pressure vessel (maximum working pressure 35 MPa), which can be rotated and operated at different angles using a custom-made stand. Temperature is controlled with an external cooling jacket and a high-capacity thermostat. The length of the pressure vessel is 2000 mm, which makes the setup suitable to study fluid flow effects on sediment geotechnical properties. Specific insets in the inflow and outflow of the vessel enable defined axial loading of the sample. In particular, the insets are designed for sand production studies, simulation of high gas flow and fluidization of sediment particles.
NESSI-FLOW
