Transient wellbore temperature and pressure calculation model for supercritical CO_2 jet fracturing

摘要

Supercritical carbon dioxide (SC-CO2) jet fracturing is a new technology, and it has many significant advantages compared with hydraulic fracturing. Ensuring the CO2 at supercritical state at the jet point is the key to the effective implementation of this technology. Therefore, this research proposes a numerical model to predict the jet point CO2 temperature and pressure for SC-CO2 jet fracturing. In this model, the effect of the tubing, casing, and cement sheath on heat transfer are all taken into consideration; the heat transfer is considered to be transient. The numerical results show that under the condition of high tubing injection rate, increase injection temperature and annulus injection rate both are not effective ways to make sure the CO2 temperature at the jet point exceeds its critical value. Therefore, in order to keep the CO2 at the jet point remains in a supercritical state, the tubing injection rate needs to be optimized. The CO2 pressure at the jet point is always exceeded its critical value during the process of supercritical carbon dioxide jet fracturing.