Kerr-McGee pioneered Gulf of Mexico spar technology with the installation of its Neptune facility in 1996. The structure, located in 1,930 ft (589 m) of water in Viosca Knoll Block 826 offshore Louisiana, was positioned to act as a hub in processing the production from phased developments in the Neptune and surrounding fields.
The facility's capacity was expanded in 1998, increasing produced-gas capacity from 30 MMcf/d to 70 MMcf/d and produced-oil capacity from 25,000 b/d to 35,000 b/d. The production increase was accomplished by adding compression, a new glycol dehydration system, larger separation equipment, and expanded oil treatment and transfer systems.

Substantial addition
A study was conducted to determine feasibility to extend Neptune's maximum gas capacity to approximately 100 MMcf/d, which later was accepted for design purposes.
Completion of the fast-track project required close coordination among the facility's operator and the other involved partner companies, detailed front-end planning, lifting flexibility without the use of a derrick barge, ingenuity to extend deck space and a restricted offshore construction schedule to maintain existing production levels with minimal disruption. All of this work was required on a platform with limited space and additional weight capacity. The offshore construction effort began in late September 2004 but was delayed several weeks due to reconstruction efforts after the departure of Hurricane Ivan.

Modules, skids added
In order to enhance the platform's capabilities, new and augmented equipment needed to be engineered, designed and installed on all three decks. The expansion hinged principally on the installation of two major modules. A compressor module was added to house two turbine-driven centrifugal compressors. The compressors were installed as boosters to achieve a pipeline sales pressure of more than 2,000 psi. Opposite the compressor module, a new cantilevered production module was added. This module consisted of three production separators for high, intermediate and low pressures.
The facility's two existing reciprocating compressors were overhauled, altering them from three-stage to two-stage machines. Every compressor scrubber was either replaced or modified. The compressor cylinders for each throw were either replaced or relocated. A vapor recovery compressor was reinstalled to restore vapor recovery capacity.
Deck extensions were needed to accommodate an allocation metering skid, flowline heaters and a launcher/receiver skid for pigging operations. A completely independent firewater system was added with two firewater pumps. A new stainless-steel flare scrubber with special internals was installed. Two 400-bbl methanol storage tanks were placed on the top deck, along with a chemical injection skid.
A new motor control center (MCC) was added to provide additional power, and an allocation metering system was installed to record oil, gas and methanol usage for the entire platform. A programmable logic controller (PLC) was added, and the majority of the existing platform controls were changed from pneumatic control to PLC control.
Weight additions were closely monitored, and structural modifications were made as necessary to accommodate the new equipment.

Piping and interconnects
All modules were assembled and test-fit at the fabrication yard and then
disassembled to a point meeting the offshore lifting capacity. The modules were then reassembled offshore. The test-fit operation saved significant manhours and time offshore.
New equipment was placed where space was available, often necessitating demolition and rerouting of existing piping. An estimated 14,000 ft (4,270 m) of new interconnecting piping was required to complete the project, along with more than 65,000 ft (19,825 m) of new cable. More than 250 individual piping tie-ins were required. During
a platform shutdown, in a 50-ft by
50-ft (15-m by 15-m) area, more than 1,500 ft (458 m) of piping was demolished and replaced with new re-routed piping. Since the original platform and initial capacity expansion were done without the use of 3-D modeling, a field crew prepared physical measurements of anticipated piping runs on site in preparation for the detailed design. That information was then entered into a 3-D software program to establish a model that identified and eliminated clashes in the labyrinth of piping needed for connecting equipment in the expanded facilities. There were minimal clashes, and very little rework was required.

No external lift
To make the project economically feasible, the decision was made to eschew the use of a derrick barge. Instead, all materials were shipped offshore on supply vessels and offloaded solely with the use of a permanent 50-ton pedestal crane and a rented 150-ton "bull-frog" crane. The temporary, girder-mounted crane could be repositioned around the top deck as needed to erect equipment and interconnect piping or to remove obsolete materials from the platform.
The heaviest lift was the base and rack for the production module, which weighed slightly less than 50 tons. One crane was used to pick the load off the supply boat, but both cranes, working in tandem, were required to complete the lift. The MCC lift was of a similar weight. In all, there were approximately 25 module sections lifted as well as piping and other equipment. The production module itself resulted in five lifts. The lifts for all equipment were performed under detailed lift plans that were in turn based on the certified weights of the equipment. It is estimated that more than 850 tons of equipment was lifted onto the platform.
The replaced equipment had to be loaded onto supply vessels for transport to shore, and its removal required precise coordination so that a proper sequence of new equipment additions and demolition could be maintained in the restricted work areas. As such, detailed scheduling of demolition was required so as not to interfere with the erection of new equipment and to maximize the number of work faces being accomplished at any one time.
Additional, non-related repairs to correct platform damage from Hurricane Ivan were also being completed simultaneously by other contractors, adding to the logistical complexity of the project.
The removal and replacement of the flare tip was completed by a modified 70-ton "bull-frog" crane. The crane had a rated capacity of 4,000 pounds at the required radius. The use of this crane made the flare tip replacement a safer and more cost-effective operation.
A 24-day shutdown was required at the end of the project to revamp the existing reciprocating compressor, replace scrubbers, replace the flare tip, complete piping tie-ins and leak-test the gas piping. There was no formal interface management function despite the closely scheduled activity. Instead, careful planning, close cooperation and communication among all project participants allowed the complicated project to move forward and be completed within the allocated 24-day turnaround timeframe.

Safety
The safety of the crews remained a priority for all parties throughout the construction. There were cost and time considerations that necessitated additional manpower, which also required additional authorization from the US Coast Guard. In maintaining that focus on safety, a very thorough environment, health and safety plan was developed that included the implementation of programs such as work-stop authority, analysis of various what-if scenarios, pre-design safety reviews, additional life rafts, a certified stand-by boat and other measures to support the additional workers.
Temporary stairs had to be constructed to provide needed emergency access of personnel while extensive demolition and fabrication was being accomplished. Additionally, emergency egress routes needed to be maintained within a forest of scaffolding.
During the hookup, more than 60 pressurized and fire retardant welding habitats were constructed onsite, conforming to Mineral Management Service (MMS) regulations, so that welding could be done while the platform was in operation.

Recap
The upgraded facility, with its modular and onsite "stick-built" design, required almost 3 miles (4.8 km) of new piping and roughly 12 miles (19 km) of new cable with only a modestly expanded footprint. Before the commissioning could be completed in August 2005, the platform had to weather four more hurricanes, including Katrina and Rita. Neptune now has more than three times its original gas-flow capacity and has reached its rated ANSI 900 pressure capacity for export through an 8-in. pipeline. The topsides weight is currently near rated capacity.

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