Thermal and hydraulic effects in the subsurface related to large scale hydrogen storage operations

Abstract:

Energy production from renewable sources such as wind or solar power is subject to natural temporal fluctuations. Therefore, energy storage will become indispensable when renewable sources represent a substantial share in the total energy production. Subsurface storage of synthetically produced hydrogen in porous sandstone formations is particularly suited for large amounts of energy and relatively long production cycles. The increasing use of the subsurface, however, demands for an a priori analysis of possible effects of a storage operation in order to minimize environmental risks and interference with other usages, such as geothermal energy storage or groundwater abstraction. In this context, this work aims at an assessment of thermal and hydraulic impacts of a hypothetical hydrogen storage scenario in an anticlinal structure in northern Germany using numerical process simulations. The storage structure consists of partially eroded Rhaetian sandstones acting as the storage formation with the upper barrier formations being mud- and chalkstones of the Lower Jurassic and Lower Cretaceous. The storage operation was modeled over a period of one year using three wells located on the flank of the structure near its top. Each production cycle was set to a duration of seven days in which an equivalent of around 280000 GJ were extracted. The numerical simulations were carried out using the Eclipse E300 simulator (Schlumberger) in conjunction with the open source THMC-simulator OpenGeoSys, where the hydraulic- and mass transport processes are solved by Eclipse and the heat transport processes by OpenGeoSys. The simulation results show that the thermal effects due to the storage operation are mainly limited to the immediate vicinity of the storage wells, thus their reach is on the decimeter to meter scale. Since heat transport is dominated by thermal conduction this also includes the sealing formations above and below the storage formation. Moreover, the propagation of thermal effects is damped by the cyclic nature of the storage operation. The effects resulting from induced hydraulic processes show a considerably larger reach of less than 10 km in lateral directions within the actual storage formation. The vertical propagation is strongly dependent on the integrity of the sealing formation atop the storage formation.