The Mechanism of Pressure Control Problem in High H2S/CO2 Gas Wells

Abstract

Abstract Supercritical fluid refers to substancees above its critical temperature and critical pressure. Critical temperature of CO2 is 31.05°C and its critical pressure is 7.38MPa. Critical temperature of H2S is 100.45°C and critical pressure 9.00MPa. The special phase behavior of supercritical state is: Lower viscosity, great density and diffusion coefficient, good mobility, sound solubility and mass transfer behavior and especially sensible to the change of temperature and pressure around critical point. Phase change of supercritical CO2 and H2S will induce serious blowout during the course of drilling and production. In this paper, the reason of well blowout induced by phase change of supercritical CO2 and H2S is discussed proceeded with special phase character by the complex calculation of relevant samples. It is possible that CO2 and H2S in high acidic gas well is in the state of supercritical fluid. Well blowout will occur because the volume of CO2 and H2S in the annulus space is dramatically expanded in annulus space near well head owing to the phase transformation. It is of great importance to discover the kick and to measure the instant annulus flow of drilling fluid during the drilling process of high pressure and acidic gas well.