With the growing energy demand worldwide, the underground storage of natural and processed gas is also getting important. DHI-WASY has carried out several projects for Geostock, a French company specialised in underground gas storage, studying the interaction of storage caverns with the groundwater system. Important topics of the studies were, amongst others:
- clogging effects at infiltration boreholes used to guarantee a sufficient water pressure to contain the gas in the caverns
- dewatering of the fissured rock mass during construction of innovative storage systems for liquefied natural gas (LNG) at extremely low temperatures
- design of infiltration systems, and
- saltwater intrusion caused by groundwater depletion due to cavern construction
The results are used by Geostock to:
- optimise the design of new cavern systems
- adapt the construction schedules according to the hydraulic situation, and to
- provide the basis for an efficient management of caverns during their lifetime
In one specific project, a FEFLOW model was set up for simulating the construction of an LNG storage cavern system over a period of four years. The first main focus was on a detailed implementation of the geometry of tunnels, caverns and the corresponding drainage system in the finite element mesh used by FEFLOW. On this basis, the dewatering of the surrounding rock mass during construction was simulated. This required implementation of temporally varying boundary conditions and material properties for the technical structures, including a drainage system, to consider variably saturated conditions (applying Richards’ equation), and to budget inflow into different parts of the cavern system in detail. Finally, a density-dependent simulation was used to determine the effect of the dewatering on saltwater intrusion from the nearby sea shores.
