Study on wellbore pressure control of the advanced dynamic well-killing Technology - Cycle and weight method during the deepwater riserless mud recovery system

Well-killing can effectively prevent blowouts and other sudden accidents, and is a key aspect to ensure the safety, efficiency, and effectiveness of oil and natural gas extraction. The deepwater riserless mud recovery (RMR) system lacks the characteristics of normal kill fluid circulation channel, relies on return pipeline chocking and adjusts the subsea pump to control pressure, so the selection of the kill method is important. Thus, this study establishes a multiphase flow calculation model of the RMR system with cycle and weight mothed and gives the solution process, simulating pressure changes at the subsea pump inlet, outlet, and standpipe under different kill methods, kill pump rates, and pit gains. The results show that the RMR system's multiphase flow model has reduced the casing pressure by 1.7 MPa compared to the traditional pure gas column calculation models, with an accuracy improvement of 10.74%. Using the cyclic and weight method to control stand pipe pressure is more manageable than traditional deepwater riser systems. It can reduce the seabed pump inlet pressure by 0.95 MPa compared to the deepwater driller’s method, and the well-killing time was shortened by nearly 50%. Unlike the deepwater wait and weight method, the stand pipe pressure does not experience multiple fluctuations, and the seabed pump outlet pressure increase time was delayed by 85.19%. This advanced method minimizes the time spent on well-killing and ensures the stability and safety of the seabed pump and suction module, which is of great significance for guiding on-site construction.