Combination of Side Entry Sub, Pad Eye Sub, and Swivel Sub Prevents Damage to Wireline Cable and Allows Heave Compensation on a Semi-submersible Rig for Pipe Recovery Operation

Abstract

Wireline pipe recovery operation on a floater type offshore rig such as a semi-submersible or drillship can be challenging when heave motion affects the wireline cable, depth accuracy, cable tension, rig-up equipment positions, and well control. The heave motion compensator (HMC) unit connected on top of the top-drive system (TDS) has a narrow gap that allows a wireline cable to pass through and could cause damage to the wireline cable. Conventional processes in performing pipe recovery operations only permit operations to occur on the open end of the drillpipe while on the rotary table. With a long bailer arm, the cable will have enough clearance to pass through the elevator then enter the TDS body, but this process also prevents the operator from establishing a barrier for well control situations because the top of the drillpipe remains open. The other issue is depth accuracy, where heave motion causes both upward and downward movement on the cable while wireline is being run in hole (RIH) or pulled out of the hole (POOH). The depth shifts due to heaving motion could cause a back-off string shot to be fired off at depth.

To overcome these issues, the Smart Sub system—a combination of a special side-entry sub (SES), pad eye sub, and a swivel sub—allows heave motion to be compensated to the top sheave and enables the wireline cable to be positioned in front of the TDS unlike the conventional method where the cable remains in contact with the TDS. The real result of this combination is studied from the pipe recovery operation performed on semi-submersible rig in Myanmar.