Synergistic Enhancement Mechanism of Multi-Component Thermal Composite Flooding with Branched Horizontal Wells in Thin-Layer Extra-Heavy Oil Reservoirs

Thin-layer extra-heavy oil reservoirs are commonly characterized by small oil-bearing thickness, high crude oil viscosity, and severe steam override. To address these problems, a multi-component thermal composite flooding method with branched horizontal wells was proposed. The method combines steam, viscosity reducer, and N2 injection. Three-dimensional physical experiments and laboratory-scale numerical simulations were conducted. The temperature field expansion, production performance, thermal sweep range, and reservoir utilization degree were compared under three development methods: steam flooding with branched horizontal wells, multi-component thermal composite flooding with horizontal wells, and multi-component thermal composite flooding with branched horizontal wells. The results show that multi-component thermal composite flooding with branched horizontal wells can effectively suppress steam override. It can also enlarge the steam chamber, improve the uniformity of reservoir heating, and enhance the production of remaining oil. The peak oil production rate reached 18.6 mL/min, and the final oil recovery factor was 56.19%. These values were 10.48 and 27.21 percentage points higher than those of multi-component thermal composite flooding with horizontal wells and steam flooding with branched horizontal wells, respectively. The numerical simulation results show that the effective heated zone ratio reached 51.14%, while the unswept zone ratio decreased to 20.30%. The enhancement mechanism is attributed to the synergistic effect of well structure, viscosity reducer, N2, and steam, which improves thermal sweep efficiency and reservoir utilization. The results provide a reference for the efficient development of thin-layer extra-heavy oil reservoirs.