Numerical Investigation on Wellbore Temperature Prediction during the CO2 Fracturing in Horizontal Wells

A novel model is established to predict the temperature field in the horizontal wellbore during CO2 fracturing. The pressure work and viscous dissipation are considered, and the transient energy, mass and momentum equations as well as the CO2 physical properties are solved fully coupled. The model passes the convergence test and is verified through a comparison using the COMSOL software. Then, a sensitivity analysis is performed to study the effects of the treating parameters. Results illustrate that the relationship between the injection rate and the stable bottom-hole temperature (hereinafter referred to as BHT) is non-monotonic, which is different from the hydraulic fracturing. The existence of the horizontal section will increase the BHT at 2 m(3)/min condition but reduce the BHT at 10 m(3)/min condition. The problem of high wellbore friction can be alleviated through tube size enhancement, and the ultimate injection rate allowed increased from 2.7 m(3)/min to 29.6 m(3)/min when the tube diameter increased from 50.3 mm to 100.3 mm. Additionally, the open-hole completion method of the horizontal section can increase the BHT to 2.7 degrees C but reduce the near formation temperature to 24.5 degrees C compared with the casing completion method.