ARCO PLATFORM GOES EASY ON THE ENVIRONMENT

ARCO Oil & Gas Co. has started producing gas with an environmentally friendly installation on Mississippi Sound north of Dauphin Island off Alabama.

The North Dauphin Island (NDI) unit platform is in 11 ft of water on Alabama State Tract 73 about 1/2 mile north of Dauphin Island.

NDI also covers parts of State Tracts 72, 90, and 91.

ARCO stressed designs and installation procedures that minimized environmental disturbance.

James D. Martin, commissioner of the Alabama Department of Conservation and Natural Resources, praised ARCO for taking extra care to protect "one of the most environmentally sensitive areas in the U.S."

Martin said, "These shallow bays are rich in marine life-shrimp, oysters, and fish. Drilling right in the middle of it and bringing pipelines from the platform to shore is a great challenge.

"ARCO met that challenge."

Jay Cheatham, ARCO Oil & Gas senior vice-president, said, "We believe this facility proves we can provide a high level of environmental protection and produce gas economically.

ARCO expects NDI to produce 80-100 bcf of gas in 10 years, with production peaking this year at 70 MMcfd. The $50 million development took nearly 2 years to complete.

Six wells have been producing 60-70 MMcfd of gas through 6 in. flow lines to the NDI platform since last December. Production is separated, dehydrated, and compressed at the platform for delivery through an 8.6 mile, 12 in. offshore sales pipeline and 4 miles of onshore line to Mobil Exploration & Producing U.S. Inc.'s Mary Ann gas processing plant in southern Mobile County, Ala.

ARCO is relaying gas through the sales line from BP Exploration Inc. wells in the federal Outer Continental Shelf of the Gulf of Mexico. Combined sales line flow is 75-85 MMcfd.

Capacity of the sales pipeline system is about 148 MMcfd.

ENVIRONMENTAL MEASURES

Before applying for permits, ARCO spent 9 months studying environmental factors and technical requirements. Specialists helping with the studies included a marine biologist, archaeologist, ornithologist, surveyors, oystermen, and property owners.

Another 9 months were required to obtain permits. Five months were required to lay pipe and install the NDI platform.

Three wells in the project were drilled in 1990, the rest in spring and summer 1991.

To protect the environment, ARCO:

Drilled three horizontal wells to minimize drilling.
Outfitted the NDI platform with a roof to prevent rainwater from becoming contaminated by washing across processing equipment on the top deck.
Painted the platform a blue-gray color scheme that blends with the horizon.
Shielded platform exterior lights to lessen night time visual distraction to local residents.
Changed the sales pipeline route to avoid areas important to local oyster fishermen.
Protected coastal wetlands from damage by boring from the beach 1,800 ft to a point offshore where onshore and offshore segments of the sales line were connected.

Pipeline contractor Torch Inc., Belle Chasse, La., used a jetting process to bury offshore flow and sales lines.

Torch first positioned pipe along the pipeline routes. Next, the company used high pressure water jets to cut a 30 in. wide trench around the pipe and 3 ft below the mud line and collected the sediment aboard a jet barge.

The pipe was allowed to slide into the open trench, and sediment was circulated to a turbidity reduction skid dragged along the floor of the sound about 200 ft behind the jet barge. A baffle system on the skid guided sediment back into the trench, covering the pipe resting on the bottom of the trench.

Burials of 10 ft were required on two pipeline crossings of the Intracoastal Waterway.

ARCO designed the NDI platform to withstand a 100 year storm, including wave crest elevation of as much as 33 ft and wind speeds that reach 166 mph.

Two Dresser-Rand reciprocating compressors, each powered by a 2,200 hp Waukesha engine, compress gas on the platform for transmission through the sales pipeline to Mary Ann gas plant.