Simulation of the Aging of a Pore Space Underground Gas Storage by Compressibility Testing

Underground storage of natural gas plays a decisive role for the reliability of energy supply. In this context the integrity of the reservoir and its seal are essential. We are currently investigating a former natural gas reservoir as possible pore space underground gas storage with respect to the safety of the structure. The reservoir system is situated within the eastern part of the Bavarian Molasse Basin (Germany). It consists of a fine grained sandstone (reservoir) overlain by a silty marlstone (seal) To check the stability and tightness of the storage strength, we carry out cyclic compressibility tests to get insight into the poroelastic behavior and its change with cyclic loading/unloading of the reservoir rock and its seal. The compressibility tests are part of the joint scientific-industrial research storage safety project SUBI. The so far carried out cyclic compressibility tests show that both lithologies differ strongly in terms of volume strain, bulk compressibility and compaction coefficient. However, frequent loading/unloading of the reservoir and its seal do not change the poroelastic parameters tremendously: elasticity prevails within both, the reservoir and its caprock, even after 20 years of simulated storage use. Further tests have to be carried out to verify the recent results.