Ancient beachfront property
ASPEN – Only about 60 miles, as the crow flies, separates the multimillion dollar mansions of Aspen from the Mamm Creek natural gas field among the mesas south of Rifle. Geographically speaking, though, they are worlds apart.
Mamm Creek is the site of one of the biggest natural gas booms in the West. More than 300 gas wells were drilled there last year, and hundreds more are expected in 2005.But in the Roaring Fork Valley, natural gas is rare.The towering derricks of drilling rigs are popping up on the ranches near Rifle like dandelions invading a suburban bluegrass lawn in summer. Yet the closest the big energy companies have sniffed around Aspen is in the extreme western edge of Pitkin County, 12 miles southwest of Carbondale.How can two areas so close geographically be so different geologically?’Super greenhouse’At one point, they weren’t all that different, according to geologists.Seventy million years ago or so, a vast body of water called the Western Interior Cretaceous Seaway stretched from the Arctic Ocean down to the Gulf of Mexico, splitting the continent in two. Colorado, known now for its dramatic peaks, was at sea level.”The Rocky Mountains didn’t exist,” said Rex Cole, a professor of geology at Mesa State College in Grand Junction.What is now the Roaring Fork Valley was on the western edge of that great sea. Kansas was on the eastern edge.New Castle was then beach-front property. Silt, Rifle and Parachute were part of a broad coastal plain that stretched west from the seaway.Braided streams and rivers originating in the higher ground of what is now central and southeast Utah meandered to the east across that swampy, heavily vegetated land mass into the sea.”Countless streams transported sediments across that broad coastal plain,” said David Uhl, a senior geologist with EnCana Oil and Gas USA, one of the major energy companies drilling in the Mamm Creek Field.Colorado had a subtropical climate at the time, so it was much warmer, humid and rainy. “It was one of the warmest times in Colorado’s history,” Mesa State’s Cole said of what was called the Cretaceous period. “Some geologists use the term super greenhouse.”Thick vegetation – which included palms and sequoias – as well as insects and micro-organisms were constantly dying and falling to the bottom of the steams and coal swamps. Then they were covered with mud and sand transported by those streams.Thinking in geologic timeThe vast methane gas deposits now being tapped were cooked up from a stew of decaying organic materials that was compressed and heated for millions of years thousands of feet below the earth’s surface. Many of those gaseous deposits are byproducts of the coal that was produced in the process, others are simply gas deposits that are separate from the vast coal beds that are a part of the Piceance Basin.”If you don’t have the organic matter to cook, you don’t have the gas,” Cole said.It’s almost inconceivable for anyone other than geologists to imagine how dying vegetation could add up to such great reserves of natural gas in the basin.”You just have to apply geologic time to it,” said Andrew Taylor, a professor of geology at Metro State College in Denver. “We’re not talking about a few years. We’re talking about hundreds of thousands of years.”The same process that was spreading sediments on the broad coastal plain was also dumping them for millions of years into the inland sea. The mud that covered the organic matter in the sea and on the plains became shale and the sand hardened into sandstone. Those rocks are known as source rocks and reservoir rocks because they contain and transport natural gas.The Williams Fork Formation of sandstone, one particular layer in the Piceance Basin, became saturated with natural gas and is targeted by energy companies drilling in the Mamm Creek Field. That type of sandstone was also found at one time in the Roaring Fork Valley as well as around Rifle.While those sediments were deposited, the earth was also going through the beginning of what geologists called the Laramide Orogeny, a slow process of mountain building. A vast land mass that included the western half of Colorado was rising or “uplifting.”Gas deposits erodedThat process lasted tens of millions of years and affected parts of Colorado, like the Aspen and Vail areas, more drastically than others. West of the Roaring Fork Valley, 55 million to 50 million years ago, parts of the earth’s crust “cupped up” or rose while other parts of the crust warped down to form what is now known as the Piceance Basin, Uhl said.That area is bounded on the north by Rangely, on the south by Grand Mesa, on the west along a line between DeBeque and Grand Junction, and on the east along a snaking line between New Castle and Marble, Uhl said.Many of the shales and sandstones that were deposited in the Piceance Basin stayed put and were buried under other layers. But in places like Aspen, Vail and Breckenridge, those shales and sandstones were gradually brought to the surface and eroded away as the Rocky Mountains rose up from what was once an ocean floor during the Laramide Orogeny. Organic matter probably wasn’t buried long enough to produce natural gas. “That’s the No. 1 reason why your readers don’t have to worry about drilling in the Roaring Fork Valley,” Uhl said.The eastern edge of the Piceance Basin extended into the Crystal River Valley, but didn’t stretch into the Roaring Fork Valley. Uhl said places like Coal Basin, west of Redstone, and Thompson Creek, southwest of Carbondale, are on the eastern edge of the Piceance Basin.Gas and oil extraction are usually associated with barren lands of sand, sagebrush and desolate rock in Colorado, but the Piceance Basin blends in with the forested mesas and aspen groves of the White River National Forest.The U.S. Forest Service made an additional 77,320 acres of the White River National Forest available for oil and gas leasing in 2003. That pushes the total acres open for oil and gas development to 132,934, or about 6 percent of the 2.3 million acres in the forest.”Based on proposals received in 2003, it appears that the forest may be in store for many busy years ahead,” an annual report predicted.Lack of faultsCoal mining and natural gas production in the Thompson Creek area as recently as the 1970s and 1980s show how it is a transition zone between the gas-rich Piceance Basin and gas-poor Roaring Fork Valley.The Wolf Creek Field, about 12 miles southwest of Carbondale in western Pitkin County, was developed in the 1950s and produced a moderate amount of gas until 1972 when its wells were capped. It is now used for underground storage of natural gas. EnCana has showed renewed interest in the old field and plans to drill an exploratory well into the Williams Fork Formation, which is deeper than where the previous drilling occurred.In the Piceance Basin, EnCana and other energy companies are targeting that Williams Fork Formation. Uhl said that between 90 and 95 percent of the natural gas in the Piceance Basin has come and will come from that formation.A lack of faults in the rock layers helps keep the gas trapped in the basin, which makes it such an attractive site for energy companies. But the gas is also trapped in what’s known as “tight sands,” unusually hard or impermeable rocks that don’t allow natural gas to flow easily in spaces between the sand grains.Uhl said drilling core samples, which geologists examine to see what type of rock they’re drilling through, “don’t look much different from cement.” Energy companies have to use more expensive techniques, such as fracturing the rock by forcing water and sand into the gas wells at high pressure, to extract the natural gas from those tight sands.The same type of rock that is saturated with gas and being drilled is evident at the earth’s surface at the Grand Hogback in the New Castle area. In that case, the Williams Fork Formation and other sandstones were exposed and tilted at the surface during uplifting, Uhl said. Natural gas that was in those rocks was able to escape.Vail, Colorado