The identification of stratigraphic ‘sweet-spot’ interval is significant in oil and gas formation evaluation. However, formation evaluation in macroscopic-scale merely provides low resolution and limited information, thus may lead to uncertainties in resource estimation. To accurately identify the ‘sweet-spot’ intervals amongst heterogeneous lithofacies, we conducted a very high-resolution and quantitative analysis from in-situ macroscopic scale to laboratory microscopic scale on the Goldwyer formation of Canning Basin, Western Australia. The comprehensive advanced well logging and slim-compact micro imager (SCMI) technologies were synthetically applied in couple with the laboratory nanoscaled experiments. The results unveiled an extraordinarily large lithofacies heterogeneity between different rock intervals, with distinguished features shown in Goldwyer Ⅰ, Ⅱ, and Ⅲ members. The most favorable lithofacies is recognized as the laminated argillaceous thermally-matured organic matter (OM)-rich mudstone, which is widely developed in Goldwyer Ⅲ as the major attributor to ‘sweet-spot’ intervals. Goldwyer Ⅲ is exclusively characterized by thick mudstone intervals (94.4%), interbedded with thin calcareous mudstones (5.5%), corresponding to a depositional environment of low-energy distal section of the outer ramp settings. Microscopically, the most favorable lithofacies in ‘sweet-spot’ intervals develop numerous OM-/mineral nanopores for hydrocarbon storage. Illite-rich lithofacies develops abundant inter-particle pores from 2 to 17 nm that mainly contribute to pore volume for free gas storage capacity. OM-rich lithofacies with higher maturity have OM-pores with good connectivity, bearing large specific surface area that is beneficial for adsorbed gas capacity.

Underground hydrogen storage has been recognized as a key technology for storing enormous amounts of hydrogen, thus aiding in the industrial-scale application of a hydrogen economy. However, underground hydrogen storage is only poorly understood, which leads to high project risk. This research thus examined the effect of caprock availability and hydrogen injection rate on hydrogen recovery factor and hydrogen leakage rate to address some fundamental questions related to underground hydrogen storage. A three dimensional heterogeneous reservoir model was developed, and the impact of caprock and hydrogen injected rate on hydrogen underground storage efficiency were analysed with the model. The results indicate that both caprock and injection rate have an important impact on hydrogen leakage, and the quantities of trapped and recovered hydrogen. It is concluded that higher injection rate increases H ${}_2$ leakage when caprocks are absent. In addition, lower injection rates and caprock availability increases the amount of recovered hydrogen. This work therefore provided fundamental information regarding underground hydrogen storage project assessment, and supports the decarbonisation of the energy supply chain.