| Description |
The project area is located in the southwest portion of the Uinta Basin, near the northeast portion of the San Rafael Swell and localized within a small delta complex that formed in Lake Uinta during early Tertiary. The delta complex encompasses dimensions approximately 4-6 miles parallel to the ancient lake shoreline, 1/2 to 2 miles out from the shoreline and 1,200 feet thick. The heart of the delta complex and Sunnyside Tar Sands is located within Amoco's Tract of Section 2 and 3, T.14S., R.14E. Portions of adjacent land contain tar sands and include areas controlled by Gibbs Heirs; St. Mary's Parish and Crosby Corporation; U.S.A. Oil and Gas Leases with Amoco as the principal lessee; and Sunnyside Municipal Watershed. The tar sands are localized within major channel and associated sheet sand deposits of the delta complex. The general attitude of the sedimentary beds is N25° with a dip of 5°NE. The major channels of the delta complex are oriented N40°to 70°E. The geometry of the major channels and sheet sands within a delta complex is illustrated in Figure 6. The geology and the geometry of the Sunnyside delta complex are readily comprehended from Photos Nos. 2-6. Numerous lateral and vertical lithologic changes exist within a delta complex and cause abrupt variations in lithology as indicated in sections A-A' and B-B*. The Sunnyside delta complex exists within the Green River Formation. Three members of the Green River Formation define the dominant environments of deposition associated with the Sunnyside delta complex. From oldest to youngest or bottom to top these are the Douglas Creek Member, Garden Gulch Member and Parachute Creek Member. The Douglas Creek Member is the delta facies and contains the principal river channels and marshes of the delta and delta plain environments. The average thickness of the upper portion of the Douglas Creek Member in the project area is 647 feet. The Garden Gulch Member represents the shore facies and contains the shoreline and shoreface environments. Gar-pike fish scales, ostracods and algal limestones are common within the Garden Gulch Member. The average thickness of the Garden Gulch Member is 316 feet. The Parachute Creek Member'is the lake facies and contains the laminated to thin bedded deposits of the delta front and prodelta environments that formed in front of the Sunnyside delta complex. The average thickness of the Parachute Creek Member in the project area is 199 feet. The lithology of the delta complex consists of fine grained sandstones, siltstones, shales and limestones plus some local conglomerates within major channels. The quartz rich sandstones are commonly well-saturated, well-sorted and fine grained with porosities of 25-30 percent. The quartzose siltstones commonly contain streaky saturation. Shales are nonsaturated except for fractures sometimes coated with bitumen. The limestones contain irregular saturation with highly saturated algal zones. The local thin conglomerates contain nonsaturated siltstone pebbles and a saturated sandstone matrix. The tar sand deposits exist within the three members of the Green River Formation. About 80 percent of the tar sands are located within the Douglas Creek Member, 12 percent of these tar sands are located within the Garden Gulch Member, and 8 percent of these tar sands are located within the Parachute Creek Member. On the average these tar sands are associated with 11 separate saturated zones. These saturated zones range in thickness from 10-265 feet and contain bitumen that ranges from 5-13 wt% bitumen, or 12-32 gals/ton or 22-57 gal/cu yd. The mining aspects of the tar sands can be separated into overburden, mineralized zone and saturated zones. As seen on sections A-A' and B-B1 the majority of the tar sands l i e within a thick mineralized zone between the bottom and top of the principal tar sands. In general the top of the principal tar sands corresponds to the top of the Douglas Creek Member. Utilizing data on Table 1, third column (near Amoco's Tract) the depth to the top of the principal tar sands averages 502 feet. The thickness of the mineralized zone averages 586 feet with 320 feet of pay zones. |
