Calculation of Wellbore Temperature and Pressure Fields and Risk Control for Deepwater Multi-Mode Managed Pressure Drilling

Deepwater drilling faces challenges such as a narrow safety density window and complex formation pressure regimes, which are prone to induce complications like kicks and losses. By adjusting fluid flow paths through a subsea rotating control device (RCD), the transition between constant bottomhole pressure managed pressure drilling (CBHP-MPD) and mud cap managed pressure drilling (MCD) can be achieved to address kick and loss issues. A thermo-pressure coupled multiphase flow model for CBHP-MPD and a bottomhole pressure equilibrium model for MCD are established in the study. The multiphase flow model is solved using the four-point finite difference method, obtaining the temperature and pressure field distributions in the wellbore under CBHP-MPD. Risk identification and control for different MPD modes are conducted, with kick tolerance determined by verifying pressure capacities at risk points, and the parameters for MCD are optimized. The results demonstrate: For CBHP-MPD, model simulations show an average relative error of 1.22% and maximum relative error of 7.21% compared with previous experimental data, proving it to be highly accurate and fully capable of satisfying engineering needs. Increasing drilling fluid circulation rate and injection temperature reduces hydrate formation zones. Appropriately raising drilling fluid density and increasing circulation rate decreases wellhead backpressure, alleviating pressure management challenges. In the case well, increasing the circulation rate from 20 L/s to 50 L/s reduces the hydrate formation zones by 27%, while the injection temperature from 10 °C to 40 °C decreases it by 47.1%, with a kick tolerance of 3.9 m3. For MCD, charts for mud cap height and standpipe pressure are developed. Rational selection of high-density mud cap combined with high-density, low-rate sacrificial fluid ensures controllable mud cap height and standpipe pressure, thereby enabling safe MCD operations.