Adaptability Limits of Steam Flooding in Edge-Water Heavy-Oil Reservoirs, Based on Quantitative Characterization of the Extreme Steam-Chambers

Offshore medium-to-deep edge-water heavy-oil reservoirs face challenges in high-pressure steam flooding due to restricted steam-chamber expansion and uncertainty in adaptability evaluation. This study focuses on steam flooding after cyclic steam stimulation in horizontal wells. Based on steady-state energy conservation, an analytical model for the extreme steam-chamber is established considering radial and vertical heat losses, and the dimensionless steam-chamber radius ratio is defined. Two-dimensional physical simulations under different pressures reveal high-pressure suppression and chemical-composite enhancement. A field-scale numerical model analyzes the effects of conversion pressure, aquifer volume, viscosity, and well spacing on the extreme steam-chamber radius ratio. The effective chamber range is defined by ≥20% incremental recovery and ≥0.12 oil–steam ratio. Adaptability charts for various aquifer volumes are constructed by comparing the extreme steam-chamber radius ratio and the effective chamber range. The results show that increasing pressure from 5.0 MPa to 7 MPa reduces the ratio from 0.40 to 0.32, while nitrogen-foam composite raises it to 0.36. A larger aquifer, higher viscosity, and wider spacing reduce the normalized chamber scale under the investigated conditions. The charts divide reservoirs into suitable, partially suitable, and unsuitable zones; weak-aquifer, low-pressure, low-viscosity, and small-spacing cases match the effective chamber range, but the suitable zone shrinks with a larger aquifer. The method supports conversion timing, pressure optimization, well-pattern adjustment, and combined measures for offshore edge-water heavy oil. The charts provide preliminary screening for similar pore-type reservoirs under the adopted technical and economic criteria.