Study on the micro-occurrence characteristics of remaining oil after multiple steam injection and production in heavy oil reservoirs

To address limitations of conventional numerical simulation in characterizing micro-scale remaining oil after multi-cycle steam stimulation and thermal instability in traditional sand-pack models, this study uses a Gudao Oilfield heavy oil reservoir as the research object. A high-temperature-resistant cemented core model combined with cryogenic fluorescence analysis was employed to investigate viscosity/rheology changes and micro-scale remaining oil distribution after multi-cycle stimulation. Results show that temperature significantly reduces heavy oil viscosity, with a maximum viscosity reduction of 97.71%. After steam stimulation, post-stimulation oil exhibits increased viscosity due to light component loss and heavy component enrichment, showing shear-thinning behavior. The steam front mainly advances along the mainstream line and diffuses toward the wings. Clustered oil accounts for 44.79% along mainstream lines, dispersed oil droplets account for 36.82% in wing areas, and connected oil reaches 44.97% at distal wings. Interlayer heterogeneity significantly affects remaining oil occurrence. In high-permeability layers, clustered oil and dispersed oil droplets increase by 6.54% and 5.48%, respectively, compared with low-permeability layers, while connected oil in low-permeability layers reaches 38.43%. This study reveals “mainstream channeling–wing retention” and “high-permeability shearing–low-permeability retention” mechanisms, providing guidance for remaining oil identification and development optimization after multi-cycle steam stimulation.