Thermophysical properties estimation and performance analysis of superheated-steam injection in horizontal wells considering phase change

• A comprehensive mathematical model is established to estimate thermophysical properties of superheated steam.
• Mass flow rate drops faster after superheated steam is cooled to wet steam.
• To ensure that the toe section of horizontal well can be heated effectively, injection rate should not be too slow.
• Mass flow rate and the degree of superheat decrease with injection pressure.
• When reservoir permeability is high or oil viscosity is low, mass flow rate and the degree of superheat decline rapidly.

The objectives of this work are to establish a comprehensive mathematical model for estimating thermophysical properties and to analyze the performance of superheated-steam injection in horizontal wells. In this paper, governing equations for mass flow rate and pressure drop are firstly established according to mass and momentum balance principles. More importantly, phase change behavior of superheated steam is taken into account. Then, implicit equations for both the degree of superheat and steam quality are further derived based on energy balance in the wellbore. Next, the mathematical model is solved using an iterative technique and a calculation flowchart is provided. Finally, after the proposed model is validated by comparison with measured field data, the effects of some important factors on the profiles of thermophysical properties are analyzed in detail. The results indicate that for a given degree of superheat, the mass flow rate drops faster after superheated steam is cooled to wet steam. Secondly, to ensure that the toe section of horizontal well can also be heated effectively, the injection rate should not be too slow. Thirdly, the mass flow rate and the degree of superheat in the same position of horizontal wellbore decrease with injection pressure. Finally, it is found that when reservoir permeability is high or oil viscosity is low, the mass flow rate and the degree of superheat decline rapidly.