In the later stage of cycle steam stimulation(CSS), the production capacity decreases and the water cut increases. As an alternative development method to cycle steam stimulation, the flue gas-assisted cycle steam stimulation(FGACSS) has been widely applied in heavy oil development. However, existing research has not been able to reveal the mechanisms of different components in different zones, making it difficult to provide effective guidance. In this paper, based on the analysis of production dynamics from typical wells in the Moltuk field, a mechanistic model of FGACSS is constructed. The different zones of action for different components are delineated, and microscopic displacement experiments are conducted to study the flow states of oil, gas, and water in different zones at the microscopic level. The research results show that, based on the distribution of different components and reservoir parameters, the wellbore to far-well region can be divided into three zones: the high-temperature zone (0-25m), recombination zone (25-100m), and increased pressure zone (100-200m). In the high-temperature zone, the main mechanism is the viscosity reduction through condensation of steam. The flow state is water-oil, with different flow characteristics in large and small pores. In the recombination zone, viscosity reduction is achieved through heat conduction and CO2 dissolution. The presence of CO2 and N2 in the gas phase increases the pressure, and the flow state at the microscopic level is water-oil-gas-oil. The hot water and non-condensable gas displace different types of residual oil. In the increased pressure zone, only N2 is present, and the pressure continuously decreases. The flow state is gas-oil. Based on the dynamic analysis of typical wells, this paper proposes a multi-composition zoning coupling mechanism, providing reference for further research on FGACSS mechanisms and adjustments to production measures.
Keywords heavy oil, flue-gas assisted cyclic steam stimulation, zonal coupling mechanism, production analysis, microscopic experiment