Ball-Type Storm Valve System Improves Safety and Saves Rig Time

Abstract

Safety and economy of offshore operations have been improved by application of a ball-type storm valve system (SVS) that can be installed without left hand rotation, thus eliminating the danger of unscrewing drill pipe joints. The new valve system is latched by setting an overshot down over a stinger and applying weight; releasing is accomplished by right hand rotation and lifting. A retrievable test, treat, and squeeze packer is installed below the valve. Design of the ball-type SVS offers these advantages:Ease of operation. When the system is set down, the ball valve automatically closes to shut the well in. Latching onto the system is accomplished without opening the ball.Since the ball valve is not opened by latching on for removal, it can be closed by setting back down in the event high pressure is detected below the SVS.Wireline equipment can be run through the SVS.High volumes of drilling fluid may be circulated through the SVS to condition the mud system prior to removing the SVS from the hole. Present paper discusses design of the valve, with operational schematics illustrating its operation. Field results are presented describing use of the SVS in stress situations and for some maintenance functions, and resumption of operations. Rig time savings are discussed. Background General To aid in rapid and safe abandonment of offshore drilling platforms and floaters in the path of oncoming storms, operators have used a variety of storm valves that enabled them to leave the drill string in the well until the storm was over. Some operators have also used the storm valves to assist in wellhead replacement and performance of maintenance to the blowout preventer (BOP) stack. Assuming that the drill string of an offshore well drilled to 8,000 ft had to be pulled to protect against an oncoming storm or for other reasons, about $16,000 in rig time could be saved on a floater, and about $8,000 could be saved on a jackup rig if the trip could be avoided by use of a storm valve. Retrievable Bridge Plugs Cup-type retrievable bridge plugs can be used as storm safety devices, however their use necessitates removal of the drill string. The weight of the drill pipe may require that it be laid down for riding out the storm. These plugs are set 250 to 300 ft below the mud line, and will keep the well under control even if the BOP stock is broken off. After the storm passes, the plug is removed and pressure is bled off. Balanced valve type plugs are best suited as storm valve devices since pressure may build up from below the plug. Hang-Off Tools The simplest of all storm safety devices is a hang-off tool, which supports the weight of the drill string by hanging onto the bare protector at the bottom of the BOP stack. Although this method avoids removal of the drill pipe from the well, it provides no well control should the BOP stack be knocked off. Retrievable Packers and Valves. Retrievable packers, in conjunction with a check valve or a balanced valve, may be used as storm safety devices. Two variations are used. P. 163^