Hydrogen injection and withdrawal performance in depleted gas reservoirs

Residual gas trapping in porous media is a key indicator of hydrogen storage and recovery performance. The injection scheme of cushion and working gases helps maintain pressure and reduce losses. However, this information is limited in the literature. This work explores core flooding experiments (using electrical resistivity for in-situ saturation monitoring) on Bandera Grey sandstones under reservoir conditions (42 °C, 1400 psi, and 5 wt% NaCl), investigating cushion gas type and injection rate effects on storage and recovery performance. Results indicate that CO₂ injection ahead of hydrogen yielded the highest storage capacity with $S_{\text{gi}}=0.255$, then CH₄: $S_{\text{gi}}=0.226$ and finally, N₂: $S_{\text{gi}}=0.216$. At lower injection rates (0.2–0.6 cc/min), CH₄ cushion gas exhibited the highest recovery (42%), whereas at higher injection rates (1.2–10 cc/min), CO₂ resulted in the highest, with 33%. These findings emphasize cushion gas's role in enhancing hydrogen storage capacity and production efficiency in depleted gas reservoirs.