What to do with gas has long been a headache for petroleum companies, particularly where a discovery is made a great distance from a market.
Supplying gas through pipelines or as liquefied natural gas have long been the main options, though much associated gas has simply been flared.
But there is growing interest in gas-to-liquids processes recently, with much of the technology based on the Fischer-Tropsch process, invented in Germany in the 1920s.
South Africa's Sasol Ltd. has the most experience of synthetic fuel manufacture in the world, having been set up to produce gasoline from coal when the country was isolated from international markets.
Sasol manufactures 150,000 b/d equivalent of syncrude from coal, and recently began operation of a pilot plant at its Secunda site, southeast of Johannesburg, to produce up to 2,500 b/d of diesel from gas.
Sasol is pushing to build its first commercial gas-to-diesel plant, a 20,000 b/d twin train unit, in Qatar (OGJ, Mar. 24, 1997, Newsletter).
In this process, gas is first converted to synthesis gas by a Sasol process, then to liquid hydrocarbons by Fischer-Tropsch, then it is upgraded to diesel fuel.
Floater plan
Now Sasol has joined with Norway's Den norske stats oljeselskap AS (Statoil) in a move which may bring gas-to-liquids technology to the offshore industry.
The companies plan to combine Sasol's gas-to-liquids know-how with Statoil's experience in floating production technology.
The intention is to develop a process plant to convert gas into synthetic crude oil, which can be fitted on a production ship or semisubmersible vessel.
Statoil had been working on its own version of Fischer-Tropsch for years, but recognized that Sasol's isolation forced it to develop synfuel technology further.
So making use of Sasol's process would enable Statoil to get floating gas-to-liquids technology into operation more quickly than it could otherwise.
The alliance plans to develop the combined technology so Statoil can utilize more of its 50 tcf of gas reserves in Northwest Europe, and so the alliance can market the technology to other operators.
Associated gas
With the Sasol/Statoil floater, the gas-to-liquids plant would carry out the first two steps of the gas-to-diesel process, so gas would be converted to synthetic crude oil.
A Sasol official explained that a floating gas-to-syncrude unit would be suitable for utilizing associated gas produced in oil fields. The syncrude would be mixed with produced crude and sent to shore.
The companies have been working together for 2 years, said the official, and have completed preliminary studies with promising results.
Though the official could not reveal details of plant capacities studied, he said Sasol and Statoil have looked at several scenarios, from extended well test and early production schemes at the small end to large scale production.
A side benefit of a gas-to-liquids floater would be elimination of wasteful flaring, but this could become increasingly valuable with tightening environmental legislation.
Copyright 1997 Oil & Gas Journal. All Rights Reserved.
