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Commercial quantities of gas can be produced from the Gallup and "Tocito" sandstones in nine fields on the southwest and west flanks of the San Juan basin. These fields are Bisti, Gallegos, Escrito, Otero, Doswell, Chimney Rock, Horseshoe Canyon, Verde Gallup, and an unnamed field. The last four fields have only one to four wells with commercial quantities of gas. Most of the gas is produced with oil. Little gas was collected from the Gallup and "Tocito" prior to 1958. Some gas is being reinjected for secondary recovery purposes.
The Gallup sandstone is the basal member of the Mesaverde group. The "Tocito" sandstone is any sandstone lens below the Gallup formation and above the Sanastee calcareous shale and limestone. All accumulations are in stratigraphic traps which have increased trapping capacity because of favorable hydrodynamic environments with downdip water flow. Bisti field is used as an example of the trapping capacity of a stratigraphic trap. The sandstone decreases in permeability updip but does not pinch out. Under hydrostatic conditions the capillary pressure of the column of oil and gas present at Bisti would be sufficient to cause much of the oil and gas to migrate updip out of the permeability lenses. However, with favorable hydrodynamics, the oil and gas column of over 360 feet is retained. >
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