Last year, over an oil field lying under the waters of the Arabian Gulf, a new, low, and decidedly ungainly framework of steel rose up against the horizon some distance off the coast of Saudi Arabia. For the Gulf, it was just another addition to such offshore oil facilities as marine drilling platforms, production wells and huge steel islands for tankers. But for the Arabian American Oil Company, it was another in a continuing series of innovations designed to improve Aramco's production of oil. The framework was the beginning of a unique offshore gas-oil separation plant, called in the trade "GOSPs", whose function is to separate gas from crude oil before the crude can be sent any distance through pipelines or manufactured into products.
Normally, GOSPs are located on shore. Aramco has 26 such plants spotted strategically near groups of oil wells in its far-flung fields. Even the plant assigned to separate the oil and gas of Safaniya, the largest offshore oil field in the world, was located on the shore overlooking the field. Now some of the separation takes place in a multi-unit plant standing on legs 25 miles out in the Gulf, relatively close to some of the field's production wells.
In an industry as complex as the petroleum industry numerous factors contribute to decisions, but in the decision to build a GOSP offshore one factor was paramount: it would raise the throughput capacity of the trunkline through which oil moves ashore and therefore increase the potential of the Safaniya field. By placing the GOSP nearer to the wells, engineers agreed, back pressure would be reduced on the trunkline and the trunkline—which would then carry only crude instead of crude plus dissolved gas—could hold and move more oil.
The plant consists of three platforms standing out in the water in a line, all connected by metal-grating walkways. The easternmost platform supports the equipment which carries out the first stage of the separation process. The structure is dominated by two huge horizontal trap vessels designed to operate in parallel to separate gas from a maximum of 450,000 barrels per day of crude oil. The rest of the gas-oil separation takes place in spheroids of a second Safaniya GOSP on the shore.
On the same platform are three booster pumps for raising the degassed crude to a specified suction pressure before the oil goes to two shipping pumps nearby which send the oil landward, through an underwater line. The separated gas is flared at a standpipe tip to the eastward.
Many gas-oil separator plants depend on an external source of electric power to work the pumps. Aramco's land-based GOSPs, for example, get their electrical power from the company's utilities system. The new offshore Safaniya GOSP, however, must be self-sufficient. The installation's central platform supports the GOSP's utility system. Inside a large windowless building on the structure is a 13,500-kilowatt gas combustion turbogenerator, usually fueled by gas just separated from crude on the adjacent platform. It is the job of this big generator to supply electric power and compressed air for the operation of the GOSP. Below the generator space on the first deck of the utilities structure is the offshore GOSP's nerve center, a commodious control room where operators superintend the running of the GOSP and the main generator which powers it.
The third platform carries a two-story building used as living quarters for the operating crews and foreman. Atop the housing structure is a helicopter port and below it, near water level, a boat dock.
Built into the gas-oil separator and utilities structures are provisions for avoiding pollution of surrounding waters caused by accidental leaks of the crude oil running through the installation. A sump system carries off drainage to special tanks where the oil separates from water by gravity and the oil collected is pumped ashore.
The remoteness of Aramco's newest GOSP requires radio communications between it and key operations centers ashore to be of a very high order of reliability. Communications via telephone are carried over a frequency diversity microwave link with the field's shore base (which in an emergency can shut the plant down with the same system). Operators in the GOSP's central control room are able to talk directly by phone with company oil and marine people. Company specialists are now working on the technical practicability of running the entire offshore operation on automatic control, which would put an end to the stationing live-aboard crews on the GOSP and eliminate several of the loneliest assignments on Aramco's roster.