Putting 'fizz' into lagging US oil fields; CO2 bonanza here will help keep crude flowing

McElmo Canyon holds a unique and hidden treasure that may soon be helping US motorists fill up their tanks.

No, this modest canyon of carved, rust-stained sandstone and ramshackle farms , which lies in the shadow of the majestic, Sleeping Ute Mountain, does not harbor another major petroleum reservoir. It overlies something even more unusual: a natural desposit of carbon dioxide.

Today, a single well owned by Amerigas taps the trillions of cubic feet of CO 2 ''slush'' formed 65 million years ago by volcanic activity and locked beneath the surface here in southwest Colorado.

Amerigas liquefies this gas for use in carbonating soda pop and freezes it into dry ice. But since the 1970s both Shell and Mobil Oil have been researching its use for a totally different purpose: recovering more oil from the nearly depleted oil fields in west Texas.

Mobil Oil Corporation refuses to comment on its plans. But Bill Scrimpshire of Shell explains that his firm is putting the final pieces together for production of the McElmo field, building a 500-mile long, 30-inch pipeline so the gas can be transported to west Texas, and then injecting it into the Denver City unit of the Wasson oil field. This half of the Wasson reservoir contained 4 billion barrels when it was discovered, Mr. Scrimpshire says. At its peak it was producing 150,000 barrels a day. Currently, its production rate has declined to less than 100,000 barrels a day. Without CO2, it will be abandoned in the late 1980s or early 1990s, the Shell spokesman explains.

An oil reservoir is a region of porous rock saturated with hydrocarbons. Often, when a reservoir is first tapped it can be pumped by natural pressure. But, on average, only one-third of the oil can be removed in this fashion.

To get the second third, oil men turn to ''secondary recovery.'' Generally, this involves flooding the reservoir with water. However, this still leaves a substantial amount of oil behind. And rising oil prices have prompted oil company researchers to investigate other, generally more expensive methods to extract more oil from existing fields. One method is carbon dioxide injection.

According to Shell, the injection of 1.2 trillion cubic feet of this gas will allow them to recover an additional 280 million barrels of crude from the Wasson: enough to extend its life by 30 years. According to the American Petroleum Institute, carbon dioxide injection could net an additional 2 billion barrels of oil from existing fields in west Texas and New Mexico.

To develop the CO2 field and build the pipeline and injection equipment to capture the additional oil from the Wasson will cost $1.6 billion, Shell estimates. This works out to $6 a barrel--a real bargain in days of more than $ 30 a barrel oil.

Shell hopes to start construction of the pipeline this summer and to be injecting carbon dioxide by 1984.