In April and May 1990, Shell Petroleum Development Co. of Nigeria Ltd. awarded Noble Drilling West Africa Inc. four separate contracts to drill oil and gas wells in the inland waterways of Nigeria.
The contracted rigs included a shallow water jack up, the NN-1, and three posted barges, the Gene Rosser, the Chuck Syring, and the Lewis Dugger.
The jack up was built in 1978, and the three posted barges are 1980s vintage. Three of the rigs have been idle for a number of years. The Shell Nigeria contracts required major modifications to the rigs before putting them into international service.
Noble replaced or refurbished all major pieces of equipment in the drilling, power, and service systems on the rigs. Rig crews serviced all other equipment. A significant amount of general service piping and electrical wiring was replaced. Each rig also required additional motor control centers to support the new drilling and mud processing equipment.
Alfa-Laval waste-heat water desalination plants and new sewage treatment units were installed on all four rigs.
Because of the tidal variances and high silt conditions expected in the African waterways, all engine cooling systems were converted from heat exchangers to radiators.
Rotary tables were made common on all rigs at 37 1/2 in. Noble had all traveling equipment completely inspected and modified as necessary. Strict attention was paid to certification and documentation of all equipment.
Safety upgrades conformed to both Shell and Noble standards. Fire and gas detection systems were installed throughout each rig. Water and foam deluge systems were installed in the wellhead areas, and new foam systems and monitors were installed on the helidecks.
THE NN-1 JACK UP
Minimum water depths specified in the contract required addition of sponsons to the bow of the NN-1 mat.
The hydraulic jacking system was completely overhauled, and a new mat jetting system was installed for shallow draft locations. This reduced deballasting time from days to less than 24 hr.
On the NN-1, the crew quarters were increased from 40 to 64 persons. A new forward quarters area built on the rig provided additional quarters and galleys for the Nigerian nationals.
POSTED BARGE RIGS
Each posted barge needed wider sponsons for better navigation in the shallow waters. By increasing the width of the posted barges, more deck area became available for the machinery and pipe racks. This additional space accommodated the extra equipment required by the contracts.
Living quarters were upgraded on the posted barges from 44 to 92 persons, with added quarters and galleys in a new upper level added on each rig.
The upper deck of the quarters also serves as a heliport, with sufficient structural strength to accommodate a Bell 212 helicopter.
The cranes on the posted barges were upgraded to accommodate the wider pipe rack and the increased operational load requirements. On each rig, a 25-ton capacity Seaking model 42 with a 60-ft boom was installed in addition to Unit model 150 and model 280H hydraulic cranes.
The drill floors were upgraded significantly to reduce congestion, and bulk material storage capacity was increased. On all three posted barges, a 40 ft x 48 ft lower P-tank and storage room were constructed between the barge deck and the machinery deck.
New state-of-the-art instrumentation was installed, and an extensive radio system was added to each rig for remote communication.
On both the Gene Rosser and the Chuck Syring, structural modifications included raising the drill floor by 12 ft for the anticipated 22-ft water depth.
On each of these two rigs, the key slot was widened from 10 ft to 20 ft to accommodate a tug during transport through the narrow African waterways.
The mud systems were overhauled to include a Brandt tandem shale shaker on the Gene Rosser. Fig. 1 shows the Gene Rosser barge rig after completion of the modifications.
On the Chuck Syring, mud pit capacity was increased from 1,400 bbl to 2,400 bbl, and two Derrick shale shakers were installed.
THE LEWIS DUGGER
Noble installed Varco top drive systems on both the Chuck Syring and the Lewis Dugger, requiring an increase in the height of the mast on each rig. Additionally, each rig was outfitted with Varco iron roughnecks and hydraulic catheads. Hydromatic brakes were upgraded to Elmago 7838 electromagnetic brakes with battery backup, and new brake cooling systems were added.
New 30 in. and 20-in. diverters with 12-in. outlets were installed on both the Chuck Syring and the Lewis Dugger.
Structural modifications on the Lewis Dugger included raising the drill floor 16 ft. This drill floor was raised higher than that of the other rigs because it needed sufficient room to handle the larger blowout preventer (BOP) stack.
A new BOP-handling system capable of handling 100 tons was placed under the drill floor.
The refurbished well control systems included a new, four-ram Hydril 13 5/8-in., 15,000-psi BOP stack and associated well control equipment. The rig also retained a 21 1/4-in., 5,000-psi Cameron double BOP with its 2,000-psi annular BOP.
Accumulator capacity was increased to meet a close-open-close requirement, and a third, remote-operating BOP station was placed at the rig abandonment station.
Specific to the Lewis Dugger is a remote, hydraulically operated, 15,000-psi choke manifold which includes two Swaco superchokes, a separate kill manifold, and a separate cementing manifold.
A third EMD 16-cylinder engine and generator, a new Ross Hill silicon control rectifier (SCR) system, and a third Gardner Denver PZ11 mud pump were added to the power systems.
A major modification on the rig was the installation of the Swaco cascading mud system. This consisted of two super shakers, three linear shakers, a desander, a desilter, a degasser, and two centrifuges. The mud system was configured for a conveyor to move oil base cuttings to a receiving barge.
The mud pit capacity was increased from 1,400 bbl to 3,000 bbl.
DELIVERY
The rigs entered the shipyard in May 1990, with the major modifications completed during the following 10 months.
The Shell Nigeria contract required Noble to provide marine support for its inland operations. Noble supplied an equipment barge for each rig and contracted with Tidex International Inc. for the services of 12 boats and 20 support barges.
Significant coordination was required from Noble, Wijsmuller Inc., the marine surveyors, and the port agent to organize the trucking, stevedoring, docking, and seafastening of the various vessels.
A central marshalling location was established in Houston to inventory, pack, and crate the massive amount of equipment and to complete all the necessary export paperwork.
Cargo barges were preloaded in the Port of Houston to reduce loading and offloading time and to minimize the variable load on Wijsmuller's two vessels, the Mighty Servant I and III, during the trip. These cargo barges contained over 100,000 ft of drill pipe and drill collars, pipe racks, Halliburton Services equipment including bulk tanks, many 20-ft cargo containers, and other rig accessories to support remote operations.
Because deck space aboard the Mighty Servant vessels was completely used during both mobilizations, it was necessary to stack empty barges on top of each other, up to four high. Fig. 2 shows the Mighty Servant III lifting the NN-1 jack up.
After delivery in November 1990, the NN-1, the Gene Rosser, six tugs, and ten barges were loaded aboard the submersible heavy lift ship, Mighty Servant III, in Freeport, Tex. The equipment arrived in Port Harcourt, Nigeria, 22 days later.
The Mighty Servant III offloaded the NN-1, three tugs, and six barges at the mouth of the Bonne River and then proceeded on a 24-hr voyage upriver to Port Harcourt. The Mighty Servant III then offloaded the Gene Rosser, three tugs, and four barges in the Escravos River. From the mouth of the Escravos River, the rig and boats journeyed 28-hr upriver to Warri.
The mouth of the Escravos River was filled with silt, resulting in a 23-ft, high-tide water depth that limited the vessels. The different floating drafts of each vessel and the swift tidal currents near both rivers complicated off-loading operations.
The NN-1 and the Gene Rosser began operation in March 1991, approximately 60 days after arrival in Nigeria.
After delivery in March 1991, the Chuck Syring, the Lewis Dugger, six tugs, and 14 barges departed Freeport, Tex. aboard the submersible heavy lift ship, Mighty Servant I (Fig. 3). They arrived in Nigeria in mid-April and were scheduled to commence operation in May.
Shell and the Nigerian National Petroleum Corp. extensively inspected and tested the rigs. These inspections included complete equipment function tests and thorough safety reviews of marine transport, aviation, and medical facilities on each rig. Nigerian National Petroleum Corp. licensed each rig after inspecting the safety systems and the conditions for the national workers.
To ensure smooth operation once the rigs arrived, Noble hired Nigerian nationals in advance of the rigs' arrival and fully trained them in operations and safety.
Noble has one inland barge and seven submersible rigs working in the U.S. and is investigating opportunities to modify these vessels for operation in the inland and coastal waters of West Africa.
Copyright 1991 Oil & Gas Journal. All Rights Reserved.