By: C. D. Morgan, editor
Hydrocarbon production in the Bluebell field is from three reservoirs in the Tertiary-aged Colton and Green River Formations: (1) overpressured Colton/Flagstaff, (2) lower Green River, and (3) upper Green River. Kerogen-rich shale and marlstone deposited in marginal and nearshore openlacustrine environments are the source of the waxy crude in the Colton/Flagstaff and lower Green River. Marlstone, or oil shale and possibly coal, are the sources for the asphaltic crude found in the upper Green River. Non-associated gas in the upper Green River could be from coaly deposits in the upper Green River, or migrated up from the lower Green River, or a combination of both. The lithology of all three reservoirs is similar; fractured sandstone, shale, limestone, and marlstone beds having generally low intergranular porosity and permeability. The strata were deposited in lacustrine and alluvial environments.
The Colton/Flagstaff reservoir can be described as a basin-center oil accumulation, whereas the upper and lower Green River reservoirs are combination stratigraphic and structural accumulations enhanced by fracturing. Petrophysical properties, facies changes, open fractures, and abnormal fluid pressure all affect the quality of the Colton/Flagstaff reservoir, but the importance of any one feature cannot be adequately quantified. Fractures and clay content have the most effect on permeability of the reservoir rocks, but neither are predictable at a scale necessary for locating well sites. The well density is too sparse to accurately map the complex heterogeneity of the beds in any of the reservoirs.
Future drilling activity in the Bluebell field will be determined by: (1) the price of oil, (2) the ability of operators to improve drilling and completion techniques, and (3) the feasibility of secondary oil recovery from the lower Green River reservoir.
Pages: 95 p.
Location: Duchesne and Uintah Counties
Media Type: Paper Publication