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OF-84-04 Estimated Oil and Gas Reserves for Rio Blanco County, Colorado

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To most efficiently estimate oil and gas reserves for the State of Colorado, a county-by-county analysis was undertaken. This report is the second in a series of oil and gas reserve investigations undertaken for those counties in which oil and/or gas was being produced at that time.

Rio Blanco County, located in northwestern Colorado, is approximately 45 miles north of Grand Junction, Colorado. The major structural features in this area are the eastern edge of the Uinta Basin, the Douglas Creek Arch and the northern half of the Piceance Basin. In this county, oil and gas are produced from, in descending order of age, the Green River {Douglas Creek) Formation, Wasatch Sandstone, Fort Union Sandstone, Mesaverde Sandstone, Emery Sandstone, Niobrara Limestone, Mancos Shale, Dakota Sandstone, Cedar Mountain Shale, Morrison Sandstone, Sundance (Entrada) Sandstone, Shinarump Conglomerate and Weber Sandstone. Gas alone is produced from, in descending order of age, the Castlegate Sandstone, Morapas Sandstone and Buckhorn Sandstone.
There are 34 fields considered active producers as of December 31, 1982. Of these, 7 are classified as oil fields (based on cumulative gas-oil ratio (GOR) of 15:1). The most significant production in this county is from Weber Sandstone in Rangely Field. In 1981, production from the Weber in Rangely accounted for 96 percent of the county total oil production and over 50 percent of the total state oil production.

Production decline curves are plotted for each currently producing horizon within each field (field-horizon). There are 74 production decline curves plotted, one for each field-horizon. Decline rates were calculated where there were sufficient production histories. Estimated oil reserves for Rio Blanco County totaled 215,231,570 barrels. The Rangely-Weber production accounts for approximately 93 percent of the oil reserves for this county. Estimated gas reserves for Rio Blanco County totaled 327,581,003 MCF. Note that the gas reserve calculations are based on a 20-year projection, therefore they do not account for gas production after the year 2002. These figures also do not account for production increases due to secondary and/or tertiary recovery not already in progress, or account for undiscovered reserves, nor do they reflect changes in economics and demand.

94 pages. Digital PDF download. OF-84-04D