Repurposing depleted oil and gas reservoirs for secondary storage may play an important role in the transition to
low-carbon energy. The integrity of the cap rocks overlying the reservoirs is an important factor for gas storage and needs to be
understood prior to repurposing. In some cases, old cap-rock cores collected during exploration and development of oil and gas
fields may be available for characterization using modern techniques but after being stored for decades these cores are likely to
have experienced many changes in moisture, which can lead to physical changes. A comparative study of samples taken from
old, unpreserved mudstone core and samples from a recently acquired and preserved core taken from the same formation shows
that the mineralogy, porosity and permeability results are relatively similar between the two cores. The differences in the
porosity measurements between the old and new core samples are primarily due to natural variations in grain size, rather than
the preservation status of the cores. Geomechanical data, however, show significant and non-systematic differences between the
old samples and the new samples, suggesting that old core samples are not suitable for geomechanical characterization. In the
absence of new, well-preserved core, old core samples may provide suitable porosity, permeability and mineralogical data,
whereas the old, unpreserved core is unlikely to provide reliable geomechanical data