Development of transient heat transfer model for controlled gradient drilling

Abstract

Accurate prediction of the wellbore temperature is critical to achieve pressure control in controlled gradient drilling. In accordance with the mass, momentum, and energy conservation principles, an integrated heat transfer model was developed for eight distinct interconnected thermal regions by considering the coupled heat and mass transfer of hollow balls, as well as the dynamic rock breaking of the drill bit. The finite volume method was employed to solve differential equations, and the dynamic layering method was employed to update the geometry and number of mesh adjacent to the moving boundary. The validity of the integrated model was verified using measured field temperatures. Using this model, the impacts of dynamically increasing well depth and mechanical energy of the drill bit on the bottomhole temperature during the dynamic drilling were compared. Additionally, the variations in temperature distribution characteristics and heat transfer efficiency, caused by the heat and mass transfer of hollow balls, were investigated. Furthermore, a sensitivity analysis of the temperature characteristics and heat transfer efficiency to the hollow ball concentration, and the position and number of cyclone separators was conducted.