A BRIEF HISTORY OF ALASKA OIL EXPLORATION & PIPELINE DEVELOPMENT
The presence of crude oil on Alaska's North Slope was suspected for more than a century. In 1968, Atlantic Richfield Company and Humble Oil (now Exxon) confirmed the presence of a vast oil field at Prudhoe Bay. Within a year, plans were under way for a pipeline.
Visiting The Trans Alaska Oil Pipeline
In 1970 environmental groups and others filed suits to prevent pipeline construction. Three and a half years of legal proceedings followed, during which the proposal to build the pipeline was considered by the federal and state governments, including the US Congress. No construction was permitted during this time.
Presidential approval of pipeline legislation provided the go-ahead to begin construction on November 16, 1973. The 360-mile distance from the Yukon River to Prudhoe Bay required a road to be built for transportation of equipment and materials. It was constructed in 1974. At the same time work was begun on pump stations, the pipeline work pad, and the Valdez Terminal.
The first pipe was laid in the Tonsina River, north of Valdez, on March 27, 1975. By the end of 1976, an additional 428 miles of pipeline were in place; miles which included Thompson Pass, a 2,678-foot high obstacle about 25 miles from Valdez
Pipeline employment reached its peak at 21,600 in August of 1975. By May of 1977, all 800 miles had been installed and tested. Oil entered the pipeline at Pump Station One, at Prudhoe Bay, on June 20, 1977, and reached Valdez on July 28. On August 1, 1977, the tanker "ARCO Juneau" sailed out of Valdez with the first load of North Slope crude oil. The historic billionth barrel reached Valdez on January 16, 1980. And, in November of 1997, the 12 billionth barrel of oil reached Valdez.
DETAILS: THE PIPELINE ITSELF
The 48-inch diameter pipeline crosses three mountain ranges as well as forests, rivers, and plains. More than half the line is elevated in sections ranging from about 30 miles in length to the a few hundred feet. The remainder is buried underground.
The decision to elevate or bury the pipe depended primarily on soil conditions and the possible effects of the pipeline heat on the soil. Normal burial was used in stable soils and rocks, where thawing would not cause loss of soil support for the pipeline. Additionally, special burial techniques were used in some short sections for animal and highway crossings.
In places where melting permafrost might create soil stability conditions, the pipeline was insulated, jacketed, and installed above ground. Thawing around the aboveground supports in the most heat-sensitive areas was and is prevented by thermal devices that carry heat up through the pipes to radiators on top of the supports.
Aboveground sections were built in a flexible zigzag pattern in which longitudinal expansion or contraction of the pipe from heat or cld is converted into sideways movement. This also accommodates pipe motion induced by earthquake.
At more than 800 river and stream crossings, the pipe bridges the waterway or is buried beneath it. And, at 151 points along the line, valves are installed to sop oil flow, if necessary. In particular, valves are located near key stream crossings, population areas, and major uphill sections of the pipeline.
Throughout much of the life of the pipeline, crude oil was moved down the line by a series of ten operating pump stations. An additional facility provided oil control capability and could have become a pump station if expansion by the system had been required. A twelfth station site was also available. Today only six of the original ten pump stations are being used to move oil through the line.(Production of oil on the North Slope has been declining because of the age of the oil fields, thereby reducing the amount of throughput of oil in the line, and thus requiring fewer pump stations.)
The heart of each station is the main pump building that houses gas-turbine-driven mainline pumps. Most stations have three pumps, each of which can move 22,000 gallons of oil each minute, or up to 754,000 barrels a day (one barrel equals 42 gallons).
THE VALDEZ TERMINAL
Oil from the pipeline is first stored, then loaded aboard tankers at the terminal in Valdez. Located across the bay from the city, this 1,000-acre site is built on the northernmost ice-free port in the United States, and offers a deep-water channel with a minimum width at the entrance of about 3,000 feet.
There are 18 crude oil storage tanks at the Terminal—4 in the West Tank Farm, and 14 in the East Tank Farm. The tanks are 250 feet in diameter, 62 feet and 3 inches high, and can hold 510,000 barrels each, for a total capacity of 9.18 million barrels. For safety, each tank is surrounded by a concrete dike, which can hold 110% of the oil in the tanks.
The nerve center of the 800-mile-long pipeline system is the Operations Control Center at the Valdez Terminal. The controllers at the center can start or stop the entire pipeline, or initiate or terminate functions at any part of the line. Other shore facilities include a vapor recovery system, a ballast water treatment plant, power plant, warehouses, and shop buildings, meters, and meter-proving equipment, water treatment and sewage systems, oil spill contingency equipment, and fire-fighting systems.
Tankers arrive almost daily at Valdez to carry crude oil from the pipeline terminal to refineries. Tanker berths at the terminal are numbered 1, 3, 4, and 5 (berth 2 could be built if needed). Berth 1 is a floating berth, and can handle tankers of 16,000 to 12,000 deadweight tons. Berth 3 is fixed, and accommodates tankers up to 250,000 deadweight tons. Berths 4 and 5 are also fixed and can each handle tankers up to 265,000 deadweight tons, or larger. Oil is gravity-fed to the ships through four hydraulically controlled metal arms. Berth 1 can load 80,000 barrels per hour. Berths 3, 4, and 5 can each load up to 110,000 barrels per hour.
The berth loading arms are also used to transfer the ship's ballast water — used to stabilize a ship at sea hen it is not carrying oil — to the ballast water treatment plant for processing. The water is treated to remove oil, then discharged 700 feet offshore into Port Valdez, at depths of 200 feet or more.