Session: 11-03-02 Well Control and Managed Pressure Drilling-2

Paper Number: 80858

80858 - Feasibility of Riser Emergency Disconnections During Drilling MPD Operations With Surface Back Pressure 

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 (Nas, 2009. SPE-119875-MS).

 

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.

 

A time domain regular wave approach is used, considering a Most Probable Maximum (MPM) methodology for 50 waves (Diezel et al, 2018. OMAE2018-77115). The disconnection is assessed eight times for each sea state, contemplating different phases along the wave cycle, spaced equally at 45 degrees, and all the phases are considered when verifying the feasibility of the sea state. For determining the feasibility of the operation, the following parameters are considered during the recoil analysis: telescopic joint collapse; slack in tensioner wirelines; compression at the riser and Lower Marine Riser Package (LMRP); and clearance from the Blow Out Preventer (BOP). The study considered a range of overpull tension, assessing the influence of the operational parameter on recoil feasibility.

 

Disregarding the same bottomhole pressure, the internal fluid pressure at the LMRP level and the pressure profile along the riser are distinct for each internal mud weight and pressure combination, consequently, it was observed that the expected location of the region under riser compression after disconnection can depend of the SBP scenario. Also, the comparison between SBP case and non-backpressure case with heavy mud weight shows that SBP lowered the compression tendency on upper riser joints for higher overpulls values, maintaining the riser more stable and less susceptible to compression and, consequently, less susceptible to buckling during the disconnection. Regarding the minimum clearance between the LMRP and BOP after disconnection it was verified that for SBP scenarios with the same bottomhole pressure the clearance increase as the SBP pressure in the riser increase. Thus, the overpull window feasible for the SBP cases are larger, allowing an operational flexibility for this parameter.

 

Besides the reduction of the non-productive time, the SBP techniques may also contribute for the safe emergency disconnection.

Presenting Author: Luan Richa Wood

Authors:

Luan Richa Wood
Germain Venero Wood
Roberto Carvalho Wood