Enhanced oil recovery (EOR) remains a major technical challenge in depleted oil reservoirs where declining pressure and reduced sweep efficiency limit hydrocarbon mobilization. Many mature fields require improved injection strategies capable of delivering stable displacement fronts and restoring reservoir energy. Despite the widespread use of methane and foam injections, their comparative performance under realistic heterogeneity conditions is not fully quantified. This study aims to evaluate methane flooding, foam injection, and gravity-assisted methane injection using a calibrated 3D reservoir simulation model to determine the most effective mechanism for improving oil recovery. A full-physics black-oil model was constructed, history-matched, and subjected to the three EOR scenarios. Production behaviour, cumulative oil, recovery factors, sweep efficiency, displacement patterns, and pressure distribution were analysed. Methane injection delivered the highest uplift, increasing cumulative oil from 3.26 × 10⁶ stb (base case) to 4.19 × 10⁶ stb, with oil rates rising from 2,850 stb/day to peaks of 4,200 stb/day, and improving the recovery factor from 29.6% to 38.4%. Foam injection yielded 3.74 × 10⁶ stb, achieving a 15% increase in sweep efficiency and reducing gas mobility by nearly 40%, which stabilized the displacement front. Gravity-assisted methane injection recovered 3.62 × 10⁶ stb, improving vertical sweep by 12% and delaying gas override. Methane flooding also demonstrated superior displacement efficiency (up to 0.71) and maintained reservoir pressure above 2,600 psia, compared with 2,320 psia under foam and 2,180 psia under gravity-assisted methane. Methane injection exhibited the strongest performance across all metrics, while foam and gravity-assisted schemes offered secondary benefits in mobility control and vertical sweep improvement. These findings provide a robust technical basis for selecting and optimizing gas-based EOR methods in depleted reservoirs.
Thompson et al. (Tue,) studied this question.