Study on the Wellbore Flow for Carbon Dioxide Fracturing

CO2 fracturing has unparalleled advantages in the reservoir reform which can significantly improve oil and gas recovery in unconventional oil and gas resources. The wellbore flow behavior is one of the fundamental issues of CO2 fracturing. A model of flow and heat transfer in the wellbore is developed in this paper, and wellbore temperature and pressure are coupled using an iterative method. The model is validated by measured data from the field. Wellbore pressure, temperature, CO2 properties, and phase state along depth are observed and a sensitivity study is conducted to analyze the controlling factors for CO2 fracturing. Results show that displacement is the key factor affecting CO2 flow behavior in the wellbore and injection temperature has greater influence on CO2 flow behavior than injection pressure and geothermal gradient; however, excess injection temperature brings enormous cost in wellbore pressure. CO2 phase state is related to working parameters and it tends to stay in liquid state under higher displacement, which is matched with field tests. This study can help optimize the working parameters of CO2 fracturing.