Evanston, Wyo. — The outlook from Chevron's mountaintop Carter Creek Gas Plant is stupendous, with ridge after snow-covered ridge of hills falling away in the distance. But the siting of the plant may have less to do with affording beautiful views than with assuring adequate ventilation.
This brand-new plant, like its Amoco-operated sister a few miles away, ''sweetens'' so-called ''sour gas.'' This is natural gas tainted with hydrogen sulfide, H2S, one of the deadliest gases occurring in nature.
The Whitney Canyon-Carter Creek gas field, northeast of Evanston, has estimated reserves of 1.6 trillion cubic feet of natural gas, plus 70 million barrels of hydrocarbon liquids and 17 million long tons of sulfur. This field lies in the 10-mile by 50-mile ''fairway'' of the Overthrust Belt. This belt, running from Alaska to Mexico, is the result of one geologic plating literally thrusting over another. This shifting created mineral deposits, most notably around the Wyoming-Utah line, where Wyoming seems to have elbowed a chunk out of Utah. The energy deposits here, which first became known during the mid-1970s, have been hailed as the greatest natural-gas find since Prudhoe Bay in Alaska in 1969.
But the energy companies must take not only the bitter, but also the sour, with the sweet, it seems. Most of the gas in this belt is sour - about 90 percent, according to Don Basko, supervisor of the Wyoming Oil and Gas Conservation Commission in Casper.
The Chevron plant has the capacity to process 150 million standard cubic feet of wellstream gas a day; this quantity, ''sweetened,'' works out to 110 million standard cubic feet of sweet gas, plus 1,000 tons a day of sulfur, and up to 4, 700 barrels a day of condensate, which is in effect high-quality light crude. This gas goes into the Trailblazer Pipeline and heads for utilities in the Midwest.
There's another new plant on the other side of Evanston: an Amoco-operated gas facility in the Anschutz Ranch East Field, which straddles the Utah line. Here condensate is brought up under very high pressure as a gas in combination with natural gas liquids and some water.
In the plant this mixture is brought under lower pressure, which causes it to separate into condensate, or oil, natural gas liquids, water, and some natural gas. This gas, plus nitrogen, is later shot back into the formation via an injection well, which maintains high pressure underground. Without this injection, pressure in the formation would fall and the condensate would not be recoverable.
All this activity has meant new jobs for newcomers and better jobs for many already in Evanston. ''People that used to make $3 or $4 an hour at a service station started making $8 or $10 or $12 in an oil field,'' one longtime resident comments.
With all these new plants in the area and expansions on the drawing boards, Evanston is expected to develop further into a local service center for the energy industry, somewhat perhaps as Casper has traditionally been on the other side of the state. The Amoco Production Company, for example, has a shiny new building just off I-80 west of town, which it will soon be filling with personnel moved from Salt Lake City.
Sizing up the picture for the state as a whole, gas commissioner Basko observed that Wyoming contributes about 4 percent of the oil and gas the United States uses.
And yet it would be a bit misleading to look at oil and gas figures together, although the two are often coupled.
''Sixty-five percent of the state's oil production is from 25 percent of the largest fields, which are up to 50 years old,'' says Mr. Basko.
The result is a steady natural decline in production - some 3 percent per year.
It would take a significant discovery to turn that decline around, he says, and it's hard to forecast any upturn in exploration activity at a time when prices of the Organization of Petroleum Exporting Countries are so uncertain and oil supplies are so abundant.
Gas is in a different situation: Major discoveries over the last few years, plus changes in federal regulations discouraging use of gas in power plants, have turned a shortage into a glut. Across the state there is ''shut in'' gas that is not being produced because there simply is no market for it. This is especially true of harder-to-produce and hence more expensive ''deep gas.''
Yet in the longer term, gas production is projected by the State Geological Survey to march smartly upward year by year even as oil is trickling off ever so gently year by year. Wyoming gas production is forecast to be 780 billion cubic feet in 1988, a more than 50 percent rise over 1982. In fact, gas production could rise 10 to 12 percent immediately, just with wells already on line, if the market were right, says Mr. Basko.
Over in Casper, Wyoming's Bob Byron of True Oil Company, Wyoming's largest independent, projects a slow but solid upturn in oil exploration through 1983 as the nation pulls out of recession and the surplus is absorbed. He offers, of course, the standard caveat that OPEC prices must hold steady.