Altamont-Bluebell—A Major, Naturally Fractured Stratigraphic Trap, Uinta Basin, Utah<xref ref-type="fn" rid="ch07fn1">¹</xref>

Petroleum geology and principal exploration plays in the Uinta-Piceance-Eagle Basins Province, Utah and Colorado

“…Its maximum width is nearly 100 miles as measured from the Book Cliffs on the south to the southern edge of the Uinta Mountains uplift. The southern flank of the Uinta Mountains uplift is probably bounded by a reverse fault (Lucas and Drexler, 1976;Hansen, 1984;Powers, 1986).…”

“…However, on the basis of oil-and gas-producing depths in Altamont wells, large volumes of gas and oil are being produced at depths below 14,500 ft. At the present time we do not fully understand how significant volumes of liquid oil can be preserved at depths deeper than the estimated oil window. The strata are highly overpressured (Lucas and Drexler, 1976;Spencer, 1987) and possibly high levels of overpressuring over long periods of time can suppress, or retard, the thermochemical reactions that usually destroy liquid oil. More research on this discrepancy needs to be done.…”

“…In the Altamont area, the dominant Tertiary reservoirs are low-porosity, naturally fractured sandstones with lesser production from limestones, fractured shales, and mudstones. The porosity of sandstone reservoirs deeper than 10,000 ft ranges from 3 to 10 percent with an average of 5 percent (Lucas and Drexler, 1976 Figure 7. Random vitrinite reflectance (Rm) measured in oil for subsurface core samples below 4,000 ft and cuttings samples above 4,000 ft. One surface sample measured.…”

“…The fields produce mostly from naturally fractured sandstones in the Tertiary Green River and Wasatch Formations. Producing reservoirs deeper than about 11,000 ft are overpressured (Lucas and Drexler, 1976;Spencer, 1987). Figure 9 shows a typical pressure profile for an oil well in the main part of the Altamont field.…”

“…The Greater Altamont trend is about 48 mi long and covers more than 400 mi 2 . Lucas and Drexler (1976) estimated the trend may ultimately produce more than 250 MMBO. Altamont has both conventional and unconventional (tight) reservoirs.…”