Numerical investigation of key parameter effects on temperature and pressure in wellbore during carbon dioxide fracturing

In the present study, a transient flow and heat transfer model considering factors of CO2 thermal properties, viscous dissipation, heat conduction, and Joule-Thomson (J-T) effect is proposed to investigate the wellbore temperature and pressure. The viscous dissipation is considered as the amount of mechanical energy converted to thermal energy. The key parameter effects on the wellbore temperature and pressure are analyzed based on investigation of a well of diameter 50.3 mm and depth 3600 m. The results show that the temperature of CO2 increases with the well depth and decreases with increasing injection time. The CO2 pressure gradient is dominated by fluid velocity. More likely, a negative pressure gradient appears more likely in deeper wells. Simulation of molecular dynamics is used to calculate the solvation free energy of solute in CO2. The results show that polyoxyethylene 23-lauryl ether is the most promising soluble substance among the studied surfactants. Polyoxyethylene 6-nonyl phenol improves the viscosity of CO2 by a maximum of 23.8% at a concentration of 5 wt.% under the condition of 323.15 K and 30 MPa. With increasing CO2 viscosity, the bottom-hole temperature and pressure vary slightly.