Impacts of reservoir permeability anisotropy on hydrogen migration and recovery efficiency in geological storage

• The impact of permeability anisotropy on hydrogen migration and recovery efficiency is evaluated. • Permeability anisotropy governs hydrogen migration, thereby affecting hydrogen recovery efficiency. • Permeability anisotropy affects the extent to which absolute permeability influence hydrogen recovery efficiency. • Well configuration should be optimized according to permeability anisotropy. Underground hydrogen storage (UHS) is a promising solution for large-scale, long-term energy storage by converting surplus renewable electricity into hydrogen for later use. Hydrogen recovery efficiency is an essential indicator for evaluating the performance of UHS. However, the impacts of permeability anisotropy, including horizontal permeability anisotropy ( k h , m a x / k h , m i n ) and horizontal-to-vertical permeability anisotropy ( k h / k v ), on hydrogen recovery efficiency have not been thoroughly investigated. This study addresses this gap with numerical simulations that couple a simplified box model and a field-realistic model based on the Ahuroa gas storage site. Our results show that k h , m a x / k h , m i n affects hydrogen recovery efficiency, and this effect becomes more pronounced at higher permeability. The difference in hydrogen recovery efficiency between k h , m a x / k h , m i n ​=1 and 10 expands from 1.3 percentage points at 100 mD to 4.3 percentage points at 200 mD. Increasing k h / k v can reduce the effect of k h , m a x / k h , m i n . In reservoirs with horizontal anisotropy, orienting a horizontal well along the minimum rather than the maximum permeability direction can reduce hydrogen recovery efficiency by up to 8 percentage points (from 78 % to 70 %), with all other conditions held constant. These findings from the box model were subsequently validated through simulations of a realistic geological site (Ahuroa natural gas storage site). This study indicates that permeability anisotropy is an important consideration in UHS site assessment. Ignoring it can result in errors in hydrogen recovery efficiency evaluation, leading to inaccurate predictions of recoverable hydrogen volumes.