sandstone - teaching hand specimen of a yellow fine-grained aeolian sandstone from the Permo-Pennsylvanian Weber Formation
The Permo-Pennsylvanian Weber Sandstone was deposited in both fluvial and aeolian depositional environments, both with a source on the ancestral Uncompahgre Uplift. The aeolian Weber is a subarkosic fine to very fine-grained sand and was deposited in a dunefield.
The source of the aeolian sand was the underlying Permian Maroon Formation. Re-lithified in the the Weber, the sandstone has an average porosity of 12% and is the major producing horizon at the giant Rangely Oilfield in Rio Blanco County, Colorado. These specimens were collected north of Vernal, Utah along U.S. Highway 191.
The fluvial Weber sediments are predominantly arkosic sandstone, siltstone and shale, which act as barriers to the migration of petroleum.
In the Rangely Oilfield, Chevron, the current owner/operator of the Weber Sand Unit, began using CO2 injection in the Weber Unit in the latter part of 1986. Had the company continued using only water-flooding, the expected total recovery from the field would have been 789 million barrels – roughly 42% of the 1.9 billion barrels of oil originally in place. By switching to CO2 injection, ChevronTexaco expects to be able to extract an additional 114 million barrels.
The CO2 for the project originates at Exxon’s Shute Creek gas sweetening plant near LaBarge, Wyoming. The gas is transported via an Exxon pipeline 48 miles to Rock Springs, where it is transferred to a ChevronTexaco pipeline which transports it the 129 miles to the Rangely field.
CO2 and water are pumped into the unit in alternating cycles and travel through the reservoir rock to drive the oil into the producing wells. As is often the case, the production stream at Rangely consists of a wide range or petroleum components, water, and gases. At the surface, this stream must be separated into its various parts to recover the petroleum as well as the water and gases that will be reinjected. Once separated, the water and carbon dioxide are treated and reinjected into the formation. The formation gas is separated into natural gas and liquefied petroleum gases (LPGs). The methane is sold in the natural gas market while the LPGs are further separated into components such as propane and butane. The recovered crude oil is then sent to Salt Lake City for refining.
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