Processes to increase the rates of oil recovery could add up to 1 million barrels of oil a day to U.S. oil production by 1985, according to a congressional study to be released today.

Called "enchanced recovery," these techniques, employing steam, chemicals or flooding, allow oilmen to recover more than the 30 to 40 per cent of the oil in reservoirs that is a average for conventional methods.

The Office of Technology Assessment estimates for 1985 are more pessimistic than earlier industry and government projections, which forecast that up to 2.3 million barrels of oil a day to U.S. markets this year.

"It is doubtful that more than about 52 billion of the remaining 300 billion barrels of oil can be recovered under economic conditions using current and foreseeable enchanced recovery techniques," the congressional study says.

Industry experts point out that while the OTA study is clearly less optimistic than earlier projections, 51 billion barrels is about one quarter of Saudi Arabia's official oil reserves. The Saudies have the free world's largest known oil reservoirs.

The United State produces about 9 million barrels of oil a day, and imports the remainder of its needs, now totaling about 17 million barrels a day. Because of the 1973 Arab oil embargo and the growing awareness that U.S. proven oil reserves have been declining (from 39 billion barrels in 1970 to 31 billion barrels at the end of 1979) there has ben an increased interest in government and industry circles in enchanced recovery techniques.

The OTA study says that methods to increase recovery "could add between 11 billion and 29 billion barrels of oil to existing U.S. oil reserves" at current world prices, now about $14.30 per barrel.

The potential remains for addition of from 25 billion to 42 billion barrels of oil to U.S. reserves if prices are allowed to go to $22 per barrel, the price industry and government analysts now consider necessary to produce alternatives to oil such as synthetic fuels from coal, OTA says.

The study notes, however, that "estimates of oil recoverable by means of enchanced methods must be interpreted with caution."

OTA based its findings on a study of 835 reservoirs, representing 52 per cent of the oil fields in the lower 48 states and the Outer Continental Shelf.

Oil reservoirs are generally spongelike rock formations, with the oil trapped in the porous space between the rack grains rather in pools. Various techniques to increase production have been utilized since the 1920s.