Experimental study on nitrogen injection for enhanced recovery in homogeneous/heterogeneous gas reservoirs

Facing the challenge of extracting residual gas in depleted aquiferous gas reservoirs and water-flooded abandoned gas reservoirs due to abandonment pressure, this study investigates the feasibility of enhancing recovery through nitrogen injection. Based on the concept of development mode transformation in mature gas fields, simulation experiments were designed to evaluate nitrogen injection in pore-water and edge-water gas reservoirs under near-abandonment or water-flooded conditions. The results show that nitrogen injection effectively replenishes reservoir energy, enhances gas seepage capacity, increases the displacement pressure gradient, and significantly improves CH₄ production. In edge-water gas reservoirs, it also reduces water invasion and releases water-blocked gas. In vertically heterogeneous edge-water reservoirs, where high-permeability layers experience water breakthrough, nitrogen injection proves particularly effective in improving recovery from low-permeability layers. This study confirms nitrogen injection as a viable method to enhance recovery in depleted and water-flooded gas reservoirs, especially in heterogeneous formations, offering a new technical approach for efficient development of near-abandoned gas reservoirs. • N 2 injection can effectively improve the recovery of abandoned gas reservoirs • Post-water flooding N₂ injection in edge water gas reservoirs effectively blocks water and enhances recovery • The gas injection location dictates post-water breakthrough gas recovery in heterogeneous water-drive reservoirs