A coupled model for CO2 & superheated steam flow in full-length concentric dual-tube horizontal wells to predict the thermophysical properties of CO2 & superheated steam mixture considering condensation

The mixture of CO2 and superheated steam (SHS) has been proved effective for heavy oil recovery by field practices. It has been proved that the development effect is closely related to the state parameters (temperature, pressure and superheated degree etc.) of the mixture. As a result, wellbore modeling is an important branch in the study of thermal recovery of heavy oil. In recent years, concentric dual-tube wells (CDTW) coupled with multi-point injection technique (MPIT) is proposed to overcome the fingering phenomenon, induced by serious reservoir heterogeneity, during the steam injection process. In this paper, a wellbore model is developed for simulating CO2 & SHS flow in a full-length CDTW. The model is solved with finite difference method on space. It is found that: (a) An injection pressure, higher than 4.1 MPa, in the integral joint tube (IJT) or an injection pressure, smaller than 4.1 MPa, in annuli are recommended to obtain a uniform steam absorption rate along the horizontal wellbores. (b) The mass injection rate at well-head condition should be close to each other to avoid un-uniform of steam absorption rate along the horizontal wellbores. (c) When phase change occurs in the annuli, the mixture temperature increases with increasing CO2 content. (d) The total length of wet steam flow in the horizontal section of the wellbores increases with increasing CO2 content.