Study of critical annulus up-returning velocity of cuttings carried by supercritical CO₂ in deviated well

Supercritical carbon dioxide (SC-CO₂) drilling technology has far-reaching application potential in unconventional oil and gas exploration and development. Since SC-CO₂ has relatively low density and viscosity, effective cuttings-carrying has become one of the key points of SC-CO₂ drilling technology. The critical annulus up-returning velocity of cuttings-carrying by SC-CO₂ in deviated well is analyzed by means of theoretical analysis and experimental test, and the feasibility of SC-CO₂ cuttings-carrying is verified. The research shows that when the well angle exceeds 13°, the particles are started in a rolling fashion. The critical annulus up-returning velocity increases with the increase of the size of cuttings, sinking degree, and temperature, and it has an opposite trend with the change of pressure. When the well angle is in the range of 50°-80°, the critical annulus up-returning velocity reaches its maximum, and cuttings are difficult to be carried. Similar results are obtained through experimental study and theoretical analysis. The study provides the theoretical support for the development of supercritical carbon dioxide drilling technology.