Influences of formation water invasion on the wellbore temperature and pressure in supercritical CO2 drilling

Aiming to study the influence of formation water invasion on the wellbore temperature and pressure in SC-CO2 (supercritical CO2) drilling with coiled tubing, this paper builds up a wellbore flow model with formation water invasion in SC-CO2 drilling with coiled tubing, based on the comprehensive investigation of the influence of viscosity, density, thermal conductivity, isobaric heat capacity and Joule-Thompson coefficient of SC-CO2. The wellbore temperature and pressure distribution were calculated by the method of coupling among these parameters. The results show that the bigger the rate of invaded formation water and the bigger the density of mixed fluid, the bigger the convective heat transfer coefficient in the annulus. Because of the Joule-Thompson cooling effect caused by nozzle throttling, the annulus Mixed fluid density increased abruptly and the convective heat transfer coefficient decreased abruptly at the well depth of about 1 900 m (about 100 m to bottom hole). Meanwhile the wellbore fluid temperature increased with the invasion rate of formation water, and the same Joule-Thompson cooling effect caused the wellbore fluid temperature to decrease abruptly at the well depth of about 1 900 m. Moreover, the wellbore annulus pressure increased with the increasing of invaded formation water quantity. But the amplitude is not obvious.