| Heavy oil,ultra-heavy oil and natural asphalt account for more than 70%of the world's petroleum resource reserves.As china dependence on foreign crude oil increases year by year,how to efficiently exploit heavy oil resources will be a major challenge for china to alleviate the increasingly severe energy crisis in the future.Steam injection is a dominant technology in the form of thermal recovery of heavy oil,but there is a low degree of longitudinal sweep efficiency and oil layer production of heavy oil reservoirs for the conventional steam flooding.The concentric double-tubing steam injection technology can enhance the equilibrium production and recovery efficiency of multi-layer reservoirs.In order to promote the further development of this technology,it is of necessity to improve the research on the vertical annulus vapor-liquid two-phase flow pressure drop coupled wellbore heat dissipation.In previous studies,the pressure drop correlation of two-phase flow in the circular tube was used to roughly characterize the pressure drop behaviors for the annulus.Furthermore,during the operation of the production well,the steam-water two-phase pressure drop change in the annulus,caused by the eccentric deformation of the steam injection inner tube,was not considered.Based on the drift flux model,in this paper,the coupling model of the pressure drop for the steam-water two-phase flow in the vertical annulus and the wellbore heat dissipation is established.Program code for C language is compiled to calculate the water vapor pressure drop in the vertical downward annulus.According to the existing field test data and Caetano's experimental data,the accuracy of the fluid holdup and pressure calculated for this model is verified.The influence of structural parameters,steam injection dryness,steam injection pressure and mass flow rate of annulus on the water vapor pressure,dryness and enthalpy of vertical annulus pipes is explored.The results are revealed as follows.In the context of the given wellbore structural parameters in this paper,with the decrease of the radius of the steam injection inner tube by 0.009 m,the water vapor saturation pressure increased by 3.026 MPa,and the dryness and enthalpy values decreased by 0.118 and 110.00 k J·kg-1 at the bottom-hole steam injection annulus,respectively.Enlarging the inner diameter of the steam injection inner pipe can increase the dryness of the water vapor in the bottom hole annulus.As the mass flow rate of the annulus ascends by 256 kg·m-2·s-1,the water vapor saturation pressure fall by 3.782MPa and the dryness increases by 0.401 at the bottom-hole annulus.Increasing the steam injection flow rate in the steam injection annulus can greatly improve the bottom hole water vapor dryness.The effect of eccentricity on the bottom-hole water vapor pressure in the vertical annulus is revealed.Simulation research indicates as follow.As the eccentricity increases from 0 to 1 in the annular geometry,from concentric annulus to fully eccentric annulus,there are increase by0.265 MPa to the saturation pressure and only decreases by 0.085 to the dryness,for the water vapor at the bottom-hole annulus.Compared to concentric arrangement,eccentrically arranging the steam injection inner pipe to increase the wet steam quality in the bottom hole annulus is not feasible. |
PDF Full Text Request