Some 300 million years ago during the Pennsylvanian and Permian geologic periods, a shallow sea covered most of the area around Rangely. Along the edges of this desert lake, the wind and the waves built up huge sand dunes.
Over the eons, the sand compressed to form a porous rock, that came to be known as the Weber formation. The geologic structure that formed the subsurface oil accumulation is a giant folded arch called an anticline. The reservoir region of the Weber that contains the oil varies from less than 100 feet thick at the edges to 950 feet thick at the center of this anticline.
In 1901, some intrepid oilmen came back and drilled the first oil well in the shallow Mancos Shale formation. But the well was a disappointment. Undeterred, the drillers kept at it. By 1903, 13 different companies had been in and out of Rangely. Yet, all this activity still resulted in just six wells producing a measly two to 10 barrels per day. Hardly an auspicious beginning for a place with oil bubbling to the surface.
In 1931, Chevron began work on the first deep well in the area, the Raven A-l (pictured above) discovery well. After more than a year of drilling, Chevron punched through the sandstone and into a vast pocket of crude. The historic well went on line in 1933, producing 230 barrels of oil per day from the Weber Sandstone at a depth of 6,335 feet, which at the time made it the most productive oil well of all time.
The Raven A-l firmly established the Weber as a major league oil field. But even then, the promise remained just a promise. Since the available market was depressed at the time, Chevron decided to cap the well soon after it came on line, and wait out the down market. The Raven sat idle for 10 long years, until the dawn of World War II.
Oil demand skyrocketed and, in 1943, Chevron reopened the Raven A-l hole. By 1947, Rangely was a booming oil camp and, later the same year, was formally proved up as a town. By 1949, the boom was in full swing in Rangely, when 478 wells, scattered across 30 square miles, were sunk in the oil-soaked Weber sandstone formation.
By 1956, the field was producing at a peak rate of 82,000 barrels per day. As of 1998, the Rangely oil field, now known as the Rangely Weber Sand Unit, has recovered more than 815 million barrels of oil from the Weber reservoir, making it the largest field in the Rocky Mountain region. With 406 producing wells and 351 injection wells, the Rangely Weber Sand Unit continues to produce about 20,000 barrels per day (about one third of Colorado's production).
Today, the Weber Basin, in addition to production from the Weber itself, about 12 million barrels of oil have been recovered from the shallower Mancos Shale, at depths generally less than 2,000 feet. The Rangely Weber Sand Unit is a "unitized" field, which means many partners own the field, but only one company — Chevron USA Production — operates the field. Almost 40 partners — including major oil companies, smaller independent oil companies, trusts, and individuals — share the expenses and benefits of the field. The Unit provides jobs for approximately 300 individuals and generates about 70 percent of the property tax revenue for Rio Blanco County.