Shaffer Inc. recently completed construction of a multimillion dollar subsea drilling system for Caspmorneftegas, an operating company in the Republic of Azerbaijan.
The subsea stack will be installed on the semisubmersible drilling rig Shelf 7 currently under construction in Astrakan in the Soviet Union. Shelf 7 will drill wells in the Caspian Sea, one of the most prolific production areas in the Soviet Union.
The main components of the 42-ft tall equipment stack are two 18 3/4-in., 10,000-psi, double-ram Shaffer model SL blowout preventers (BOPs); two 18 3/4-in., 5,000-psi Spherical BOPS; the connectors; and the flexjoint (Fig. 1).
The project also includes a 21 1/4-in. diverter system. The SL BOPs are outfitted with shear rams and Multi-Ram pipe rams capable of closing around pipe from 3 1/2 in. to 5 in. OD. The other BOPs can accommodate pipe up to 17 in. OD.
The ram BOP has a working pressure of 10,000 psi and a test pressure of 15,000 psi. The Spherical BOP has a working pressure of 5,000 psi and a test pressure of 10,000 psi. The equipment is trimmed for H2S operations.
The entire stack was hydrostatically tested to 10,000 psi in its actual working configuration. Two engineers from Caspmorneftegas spent 2 months in Houston monitoring progress and documenting testing on the subsea system, The Azerbaijani engineers received specific training for this subsea stack.
Rig-up for the testing took 10 days, with actual testing of BOP components lasting 8 days. Rigging down the test equipment took another 2 days, and 5 more days were required for the final painting of the system. The testing was unique in that the customer's accumulator and control system were used; ordinarily, all of the customer's equipment may not be available for simultaneous testing with the stack.
The surface components of the control system include the following:
- Hydraulic power units and accumulator bottle rack assemblies
- BOP control manifold for selection of the active subsea pod and activation of the appropriate pilot line for ram control
- Diverter control manifold
- Driller control panel for remote control of the stack and diverter from a Zone 1 hazardous area
- Toolpusher control panel for remote control of the stack and diverter from a safe area
- Event sequence recorder for logging all manual and remote commands and alarms
- Umbilical hose reel assemblies for storing the yellow and blue subsea pod control umbilicals.
The subsea control system components consist of the following:
- Two identical multiline control pods for quick control of the BOP elements
- Acoustic backup safety system for operation of the BOP stack in the event of failure of both of the subsea control pods
- Accumulator bottle assembly dedicated for the acoustic backup system.
Because of its large size and weight, the subsea stack was disassembled into three smaller sections prior to shipment from Houston in early November. The entire subsea stack weighs over 360,000 lb: the lower marine riser package, 88,680 lb; the upper main frame, 155,200 lb, and the lower main framer 118,500 lb.
Shaffer also supplied the Shelf 7 with Rucker motion compensation equipment, including a 400,000-lb capacity drillstring compensator. The equipment package included four 16,000-lb guideline tensioners and four 80,000-lb twin riser tensioners capable of applying a total of 640,000 lb tension to the riser pipe.
The stack will enter Russia at the port of St. Petersburg, where it will travel via inland waterways to the Caspian Sea.
Because of transportation delays caused by winter weather and the supply of other systems necessary for drilling the well, the stack will not enter service until 1993.
Copyright 1991 Oil & Gas Journal. All Rights Reserved.
