Feasibility of Riser Emergency Disconnections During Drilling MPD Operations With Surface Back Pressure

Abstract

Managed-Pressure Drilling (MPD) techniques are used by operators to reduce the non-productive time associated with kicks, losses and well-control events. There are different MPD techniques applied to work reservoirs where fluid loss are common, or where the fracture gradient and the pore pressure are close [1]. MPD techniques on deep water drilling operations can lead to extreme scenarios for the riser integrity, with low effective tension scenarios for Floating Mud Cap Drilling (FMCD) up to high effective tension for Pressurized Mud Cap Drilling (PMCD) and Surface Back Pressure (SBP). Feasibility of drilling operations using MPD techniques will depend, among other factors, on the feasibility of the riser disconnection on an emergency scenario, which present restrictions due to the distribution of effective tension and axial forces along the riser. Recoil analysis is required to define safe windows for emergency disconnection during MPD operations. The critical parameters during emergency disconnection of a riser with MPD have been studied based on recoil analyses, which were performed for ultra-deep water for a range of SBP scenarios and for a non-pressurized operation with equivalent bottomhole pressure. Numerical simulations are applied for solving the transient problem of the riser disconnection in the time domain, considering the mud outflow, the riser dynamics, the vessel response and detailed tensioning system model to properly capture the system behaviour during the disconnection. Individual and comparative results are presented, and conclusions describes the influence of the SBP usage for the riser integrity during an emergence disconnection.