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<p>Foam can improve gas-EOR sweep in carbonates, but performance depends on gas identity and operating conditions. Foam deliverability and the resulting additional recovery may be strongly limited by gas type and the pressure–temperature window, while pore-scale mechanisms remain insufficiently constrained. Here we compare N<sub>2</sub> and CO<sub>2</sub> invasion regimes, assess foam deliverability across the tested pressure window, and quantify recovery gains relative to the preceding gas stage. We combine 4D-µCT with pressure monitoring to link macroscopic mobility control to pore-scale oil redistribution during nitrogen and carbon-dioxide floods followed by foam post-flushes in limestone mini-cores at 50&#xa0;°C. Foam was generated with NPEO9-AS at 65/35 gas–liquid. Stop-flow scans captured gas and foam flooding stages. On the tighter rock, N<sub>2</sub> shows an early ΔP peak followed by decline with injected pore volume, indicating channelization along a preferential path. In the more permeable rock, CO<sub>2</sub> exhibits a gradual ΔP increase with pore volume and a distributed, film-controlled advance without an early dominant channel. Foam response reflects deliverability: N<sub>2</sub> foam produces a strong resistance increase and diversion into previously bypassed pore space, whereas CO<sub>2</sub> foam does not reach the core at 8&#xa0;MPa (supercritical) but is delivered at 6.5&#xa0;MPa (subcritical), increasing resistance and mobilizing additional oil. In both systems, additional recovery originates from intermediate pores (0.20–0.35&#xa0;mm), while the smallest pores retain most residual oil. Overall, the use of 4D-µCT and pressure-derived metrics (ΔP, RF, MR) provides a practical basis to interpret mobility control and diagnose pressure-window sensitivity of gas/foam flooding in carbonates.</p>

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Pore-Scale N2 and CO2 Gas and Foam Flooding in Carbonates: Foam Deliverability and Oil Mobilization Under Constant-Rate Injection with Backpressure Control

  • 期刊论文

  • 发表日期：

    2026年3月31日

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  • Rail Kadyrov,
  • Evgeny Statsenko,
  • Thanh Hung Nguyen,
  • Emil Badretdinov

摘要

Foam can improve gas-EOR sweep in carbonates, but performance depends on gas identity and operating conditions. Foam deliverability and the resulting additional recovery may be strongly limited by gas type and the pressure–temperature window, while pore-scale mechanisms remain insufficiently constrained. Here we compare N2 and CO2 invasion regimes, assess foam deliverability across the tested pressure window, and quantify recovery gains relative to the preceding gas stage. We combine 4D-µCT with pressure monitoring to link macroscopic mobility control to pore-scale oil redistribution during nitrogen and carbon-dioxide floods followed by foam post-flushes in limestone mini-cores at 50 °C. Foam was generated with NPEO9-AS at 65/35 gas–liquid. Stop-flow scans captured gas and foam flooding stages. On the tighter rock, N2 shows an early ΔP peak followed by decline with injected pore volume, indicating channelization along a preferential path. In the more permeable rock, CO2 exhibits a gradual ΔP increase with pore volume and a distributed, film-controlled advance without an early dominant channel. Foam response reflects deliverability: N2 foam produces a strong resistance increase and diversion into previously bypassed pore space, whereas CO2 foam does not reach the core at 8 MPa (supercritical) but is delivered at 6.5 MPa (subcritical), increasing resistance and mobilizing additional oil. In both systems, additional recovery originates from intermediate pores (0.20–0.35 mm), while the smallest pores retain most residual oil. Overall, the use of 4D-µCT and pressure-derived metrics (ΔP, RF, MR) provides a practical basis to interpret mobility control and diagnose pressure-window sensitivity of gas/foam flooding in carbonates.