Temperature and pressure characteristics of the deepwater riserless drilling in the polar cold sea

The riserless drilling system offers superior well control, aiding in the prevention of drilling accidents and compliance with environmental standards in the polar cold sea. Predicting the temperature and pressure in such systems is crucial for operational safety. However, the behavior of drilling temperature and pressure in the polar cold sea remains unclear. This study applies non-Newtonian fluid mechanics and thermodynamic principles, considering the effects of mechanical energy input, hydraulic energy, and rock fragmentation at the drill bit to develop a coupled mathematical model for the temperature and pressure of riserless drilling systems in the polar cold sea. Using state-space methodology and control theory, the temporal distribution patterns of the temperature and pressure were determined. Sensitivity analysis revealed that flow rate significantly affect system temperature, with an optimal value for cooling at the wellbore bottom. Beyond this value, the heat removed by the drilling fluid diminishes. In polar cold sea regions at depths exceeding 600 m, increasing the input temperature of the drilling fluid has minimal effect on maintaining the fluidity of the drilling fluid at the seabed. The influence of cold seawater on the pressure loss of the drilling fluid within the pipeline is minimal, with a pressure increase of 0.9% after stopping the pump for 1 h. In contrast, cold air significantly impacts the pressure loss, resulting in a 12.5% increase after stopping the pump for 1 h. Insulation can maintain the fluidity of the drilling fluid, reducing the opening pump pressure required for operations.