Modeling of saturated steam circulation in full-length horizontal wells

Heavy oil reservoirs possess significant development potential, with preheating playing a key role in enhancing recovery. However, research on saturated steam circulation in full-length horizontal wells remains insufficient. This study establishes a cyclic preheating model for saturated steam in a full-length wellbore, based on mass and energy conservation equations. To improve the accuracy of calculating steam thermophysical properties along the entire wellbore, an enthalpy gradient algorithm is introduced for the first time. Using this model, a comprehensive analysis is conducted on the characteristics of typical curves, sensitivity factors, and dominant influencing parameters. The results indicate that, in comparison with simulations from the Computer Modeling Group and field monitoring data, the proposed model achieves a maximum relative error of only 3.83%, demonstrating its reliability. Among all injection parameters, the steam injection rate is the only one exhibiting a critical threshold, below which gravitational effects facilitate elevated steam temperatures in the horizontal annulus. The simulations also reveal that steam quality and temperature vary independently within the wellbore, with gravitational forces exerting a greater influence on steam temperature reduction in the vertical annulus than on steam quality. To enhance both the magnitude and uniformity of reservoir heat absorption while minimizing thermal losses, a strategy combining higher injection pressure, lower injection rate, and reduced steam quality is recommended. Importantly, steam temperature is identified as the dominant factor affecting preheating efficiency in heavy oil reservoirs. Therefore, parameter optimization should focus on achieving a high and uniformly distributed steam temperature along the horizontal annulus.