A Wellbore Flow Model of Coiled Tubing Drilling with Supercritical Carbon Dioxide

Supercritical carbon dioxide (SC-CO2) drilling technology is a new type of drilling technology, which has developed rapidly since the end of the last century. With lower jet erosion threshold pressure, higher jet erosion speed, and excellent hole cleaning capabilities, the SC-CO2 drilling receives much attention. However, for SC-CO2 fluid, the density, viscosity, heat capacity, Joule-Thomson coefficient, and so on are more sensitive to changes of wellbore temperature and pressure, and at the same time the change of parameters will react to the wellbore temperature and pressure, so they should be widely investigated while drilling with SC-CO2. The wellbore temperature and pressure coupled flow model was developed for SC-CO2 drilling, and then the wellbore pressure, temperature, and density profile were analyzed in an example. The results showed that the calculation results have a larger difference between this model and the reference model; the main reason is that the viscosity, isobaric heat capacity, thermal conductivity of SC-CO2, etc. were deemed as a fixed value in the reference model, and the wellbore temperature and pressure were not coupled while calculating.