Custom designed subsea and surface blowout preventer (BOP) stacks are awaiting installation in Shell Offshore Inc.'s deepwater Auger oil and gas field development project in the Gulf of Mexico.
Cooper Oil Tool and Shell engineers designed the BOPs specifically for Auger, a project scheduled to see use of a tension leg platform (TLP) in 2,860 ft of water in Garden Banks Block 426. Installation late this year will set the stage for a water depth production record in the gulf.
The field holds about 220 million bbl of oil equivalent reserves.
Auger's BOP stacks were delivered to McDermott Inc.'s yard in Amelia, La., last January. The equipment will be stored until the TLP hull is delivered later this year.
SUBSEA STACK
From the seabed up, the subsea BOP stack consists of a Cameron model HC collet connector; two 18 1/4 in., 10,000 psi Cameron double U II-B ram-type preventers; an 18 3/4 in., 5,000 psi annular preventer; a Cameron model HC collet connector; a second 18 3/4 in., 5,000 psi annular preventer; an 18 3/4 in. flex joint; and an 18 3/4 in. x 21 in. riser adapter.
The subsea stack is divided into two units - the lower marine riser package and the lower BOP package - for storage on the TLP. Subsea Ventures Inc. built the frame to integrate all BOP and control equipment and pressure tested both stacks. The surface stack also has an integrated frame to facilitate work on the TLP.
Each bonnet is fitted with a wedgelock assembly.
This hydromechanical lock was altered to include sequenced locking. The sequence valve prevents the wedgelock from locking until the rams are in the closed position. The U II-B preventers have separate close and lock functions. When opening pressure is applied to the rams, the wedgelock moves to the unlock position before the rams can open.
Instead of balance chambers on the wedgelock on each bonnet, a single hydrostatic balance chamber serves the four locks on either side of the stack. The balance chambers ensure that the wedgelocks do not unlock because of hydrostatic head pressure and maintain fresh BOP control fluid in the mechanisms.
Replaceable wear pads were added to the bottom of the rams of the U II-B BOPS. The two double U II-B BOPs will be fitted with two sets of shearing rams, one set of 5 1/2 in. pipe rams, and one set of variable bore rams for 3 1/2 in. to 5 1/2 in. pipe.
The U II-B preventers were built with bonnet seal carriers to replace the seals used on previous models. With the seal carriers, sealing capability is not dependent on bonnet bolt torque.
The guidelineless subsea BOP stack is fitted with separately retrievable control pods to simplify maintenance on the seabed.
SURFACE STACK, CONTROL SYSTEM
The surface BOP stack has two 11 in., 10,000 psi Cameron U BOPs (a single and a double), and an 11 in., 10,000 psi Cameron D annular preventer. Also, one additional U BOP is for use as a storm closure. Wear pads were added to the rams for the 11 in. BOPS.
The U BOP surface stack has two sets of 31/2, in. pipe rams and a set of Cameron DS shearing blind rams. The fourth cavity has a set of blind rams.
The BOP control system will have provisions for a surface diverter and a subsea diverter assembly. The two major subsystems will control the subsea BOP or subsea diverter and the surface BOP with surface diverter and associated valves. Each subsystem has a hydraulic power unit with accumulators, master hydraulic control panel, and remote electric panels.
Copyright 1993 Oil & Gas Journal. All Rights Reserved.
