Laboratory Quantification of Hydrogen Injection and Flow Parameters in Water-Bearing Rocks

Large quantities of hydrogen will need to be intermittently stored and produced if hydrogen is to play a meaningful role in the global energy system. Storage of hydrogen in natural subsurface formations, such as aquifers and depleted oil and gas reservoirs, is the only viable option considering the very large storage volumes required. Obtaining accurate laboratory data is vital for reliably assessing and predicting the performance of underground storage of hydrogen. In this work, we have used high-pressure and high-temperature coreflood rigs capable of handling large rock samples and equipped with X-ray in-situ saturation monitoring systems and robust experimental procedures to perform a comprehensive series of experiments to investigate the main parameters pertinent to hydrogen storage in water-bearing rocks. Hydrogen/water relative permeability point (k_r) as a key two-phase flow parameter was obtained from the results of these experiments. To investigate the impact of rock type, four different rock samples were used in this study which included sandstone, carbonate, outcrop rock, as well as reservoir rock samples. To minimise laboratory artefacts, large core samples were used in the experiments. Tracer tests showed that although all four rock samples had comparable tracer adsorption curves, the reservoir core was the more homogenous core plug. This observation well agreed with MICP results. In addition, the effect of gravity on relative permeability was assessed. In this paper, we also present an up-to-date and thorough review of the available literature on measured hydrogen k_r in water-bearing rocks. We compare the results of our study with those found in open literature. This comparison reveals several discrepancies and highlights some serious shortcomings of the previous measurements. The results show that our measured end-point hydrogen k_r is an order of magnitude higher than the previously reported values. We attribute this difference to the impact of the capillary end effect and the short length of the rock samples used in most of the previously reported data. Our results also reveal that, if no major heterogeneity exists in the rock sample, rock type (sandstone versus carbonate) alone has no major impact on the hydrogen saturation in the rock or on hydrogen breakthrough time. Our results show that there is a relationship between initial H₂ saturation and the porosity of rocks, that is, the initial H₂ saturation increases with increasing porosity. No clear relationship was observed for permeability, for the conditions of our experiments.