Phase control of downhole fluid during supercritical carbon dioxide fracturing

Abstract

AbstractTo control the carbon dioxide phase more effectively during supercritical carbon dioxide fracturing, a fully coupled mathematical model is proposed for the investigation of the wellbore temperature and pressure. Our model assumes that the heat transfer is steady in the wellbore but unsteady in the formation. The physical parameters of carbon dioxide vary with temperature and pressure, and the influence of casing, tubing, and cement sheath thermal resistance on heat transfer are all considered. The heat generated by fluid friction losses is also taken into consideration. Based on this model, the influence of the injection temperature, injection rate, tubing roughness, and geothermal gradient on the wellbore pressure and temperature are discussed. The results indicate that the wellbore carbon dioxide temperature increases as the injection temperature, injection rate, tubing roughness, and geothermal gradient increase, and the wellbore carbon dioxide pressure decreases as the injection temperature, injection rate, and tubing roughness increase. To ensure that the carbon dioxide is in the supercritical state when it enters the formation, engineers need to increase the injection temperature. The heat generated by fluid friction losses has a significant impact on the wellbore temperature and pressure; this effect should therefore not be ignored. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.