Experimental and numerical simulation analysis of the sealing properties of caprocks for underground gas storage safety

Caprock sealing capacity is a fundamental aspect of the safe implementation of underground gas storage systems, which serve as a foundational solution for the decarbonization of the energy matrix and the transition toward a new and more sustainable energy mix. This study implemented a multidisciplinary approach combining laboratory tests and numerical simulations for the investigation of the sealing efficiency of the caprock. Different core samples from a reference formation (Scioto Sandstone) were investigated via routine core analyses for the determination of porosity and absolute permeability, and their characterization was complemented by data from technical literature. A series of step-by-step laboratory tests were performed to measure the breakthrough pressure (i.e. threshold pressure) for the quantification of the sealing efficiency: the focus was on the influence of the temperature and the length of the core samples on the test results. Furthermore, the lab tests were reproduced via numerical simulations in COMSOL Multiphysics ® to obtain a full understanding of the phenomenon from theoretical and experimental views. The laboratory tests showed a negligible effect of temperature on the measured threshold pressure, whereas the influence of sample length on this value remains uncertain due to the counteracting effect of increased permeability in the longer core sample. The numerical simulations were able to reproduce, with some limitations, the key results of the laboratory tests.