Performance Evaluation of Enhanced Recovery Efficiency for Oxygen-Reducing Air Huff and Puff in Tight Reservoirs

This study investigates the dynamic evolution and efficacy of oxygen-reducing air huff-and-puff (HnP) for enhanced oil recovery in tight reservoirs, employing a novel large-scale two-dimensional plate model (30 × 30 × 3.5 cm) and a single-dimensional elongated core to simulate oxygen-depletion processes across 13 HnP cycles. Through systematic experimental trials, we examined key operational factors─well shut-in duration and production pressure differentials─to quantify recovery efficiency. Results reveal that oil displacement is primarily driven by pressure-difference-induced fluid dynamics (63.04% of total recovery), with diffusion-mass transfer as a secondary mechanism (36.96%), highlighting minimal light hydrocarbon extraction and limited crude oil fractionation capacity. Crucially, HnP performance is governed by shut-in duration and pressure differentials, with a single cycle categorized into three distinct stages: single-phase gas flowback, free gas drive, and declining productivity. The free gas drive stage dominates oil production, evidenced by the gas-to-oil ratio, oil rate, and bottom-hole pressure variations, underscoring its critical role in optimizing recovery strategies for tight reservoirs.