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The Bar-X, San Arroyo, and Westwater Creek natural gas fields are located on anticlinal structures having the same names, in townships: T. 16 & 17 S., R. 24, 25 & 26 E., Grand County, Colorado. The first gas in the region was discovered on the Bar-X anticline in 1948 by Stanolind Oil and Gas Company. However, further drilling was not accomplished until 1954. Development of the fields has been slow due to the lack of a market for the gas, inadequacy of the present pipeline gathering system, and to controversial estimates of the natural gas reserves.
To date, 35 wells have been drilled on the three structures with 28 of the wells completed as gas producers from one or more sands in the Dakota, Cedar Mountain, Morrison and Entrada formations. The initial production of the gas wells in the three fields has ranged from 250 MCF to over 20,000 MCF of gas per day. The B.T.U. of the gas varies from 550 to 1,150 with the lower values being confined to the gas from the Entrada formation.
The subject area is located in and near the Book Cliffs which bound the southern end of the Uinta Basin. Much of the area is extremely rugged, being dissected by deeply incised canyons and prominent cliffs. Development is largely confined to the canyons in the Book Cliffs and to the rolling terrain at their base.
The pay zones in the Dakota, Cedar Mountain and Morrison formations are largely discontinuous sandstone lenses. The lithology of these formations is extremely erratic and virtually no two adjacent wells are completed in the same sandstone bed. The Dakota sands in the San Arroyo field are the most continuous. The natural gas found in the Dakota, Cedar Mountain, and Morrison formations is primarily accumulated in stratigraphic traps. Structural control may be secondary. The over-all general region might be considered as a potential reservoir with the sandstone lenses providing concentrated accumulations within the larger reservoir. Perhaps artificial stimulation at the proper interval might result in obtaining commercial gas production, even though a porous sandstone lens was not penetr ted by the well bore. A lower salt water contact has not been established in the area for these formations. Natural gas production has been obtained in the Dakota formation all the way from 3,000 feet above sea level down to sea level. An upper water contact at an elevation of 3,200 feet has been fairly well established . This may infer that some peculiarities due to pressure variations caused by hydrodynamic and saline anomalies are present.
The gas in the Entrada formation is probably controlled by structure since the Entrada sand is a fairly continuous body.
Faulting in the region apparently has not affected the migration and accumulation of the gas, but has quite definitely affected the porosity of the sands adjacent to the faults.
The natural gas reserves estimated in the three fields vary considerably. Based on volumetric calculations using the porosity, pressure, sand thickness, and similar data, estimated reserves of natural gas in place vary from 2.5 billion to 8 billion cubic feet per section from the Dakota, Cedar Mountain, and (or) Morrison formations. The reserves, based on volumetric calculations, in the Entrada vary from 8 to 15 billion cubic feet per section.
The Bar-X field is the only field in the group which has a production history, having produced for approximately three years. Pressure-decline curves on the wells in this field for the Dakota and Morrison formations indicate minimum reserves of 1.5 to 5 billion cubic feet per section.
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