| Description |
The Sunnyside tar sands are located within the southwest portion of the Uinta Basin and localized within a small delta complex that formed in Lake Uinta during early Tertiary time. The essence of the Sunnyside tar sands deposit is a sequence of laterally continuous sheet sands or stacked bituminous sandstone deposits alternating with red, green or gray shales. Amoco controls some seventy percent of the mineable tar sands within the entire Sunnyside deposit. Within the southern area the tar sands are mainly centered on the Amoco-Kaiser tract. Within the northern area the tar sands are largely localized within the Amoco hydrocarbon leases. The Sunnyside tar sand deposit represents an elongated wedge of bituminous sandstones 500-1000 feet thick distributed along eight miles of the Roan Cliffs and extending downdip or into the cliff for one to two miles. The tar sands are localized within five to eleven separate sandstone zones. These saturated zones range in thickness from 10-265 feet and contain bitumen that ranges from 5-13 weight percent or 12-32 gallons per ton. The numerous tar sand deposits represent channel, channel mouth bar and beach bar deposits that locally thicken and thin but form relatively continuous sheets of bituminous sandstones. The general attitude of the sedimentary beds is N25-40 W with a dig of 5-7 NE. The major channels of the delta complex flowed toward N40-70 E. Numerous lateral and vertical lithologic changes exist within the Sunnyside delta complex and cause abrupt or gradual variations in the lithology and tar sand distribution. Examination of Photos 1 through 10 will help to comprehend the geology and the geometry of the Sunnyside tar sand deposit. The Sunnyside tar sands deposit exists within the Green River Formation. Three members of the Green River Formation are well-exposed along the Roan Cliffs and 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 as seen in Figure 23. The Douglas Creek Member represents the delta facies and within the southern (Amoco-Kaiser Tract) area contains the principal bituminous sandstones with intervening red shales. The Douglas Creek Member contains the principal channels, distributary channels and marshes of the delta plain and delta environments of deposition. The Douglas Creek Member is about 1,300 feet thick but only the upper half may contain tar sands. Within the Bruin Point subdelta the Douglas Creek Member averages about 500 feet thick to the base of the tar sands. The Garden Gulch Member represents the shore facies and within the northern (Hydrocarbon Lease) area contains the principal bituminous sandstones with intervening green shales. The Garden Gulch Member contains the principal distributary channels, channel mouth bars and beach to nearshore bars of the delta and lacustrine environments of deposition. Tar sands, green shales and limestones characterize the Garden Gulch Member and gar-pike fish scales, ostracods and algal limestones are common features. The average thickness of the Garden Gulch Member is about 500 feet. The Parachute Creek Member is the lake facies and contains the laminated gray shales and thin bedded deposits of the outer delta front and prodelta environments of deposition. The Parachute Creek Member has an average thickness of 130 feet and contains limited tar sands. 4. The lithology of the Sunnyside delta complex consists of sandstones, siltstones, shales and limestones plus some local thin conglomerates within channel and channel mouth bar deposits. The fine grained to very fine grained quartz-rich sandstones are well-sorted with porosities of 25-30 percent and are usually well-saturated above the paleo oilwater interface. The quartzose siltstones commonly represent levee deposits and contain moderate to streaky saturation. Shales are nonsaturated except for fractures coated with bitumen in areas adjacent to tar zones. Red shales commonly formed in marsh environments, green shales usually formed in shallow water nearshore environments and gray shales formed in moderate water depths of lacustrine environments. The limestones formed in shallow nearshore environments and contain irregular saturation with highly saturated algal zones. The local thin conglomerates contain nonsaturated siltstone or limestone pebbles and a saturated sandstone matrix. Various aspects of the lithology are summarized in Table 10. 5. The Sunnyside delta complex has been defined on the distribution of tar sands and contains fluvial and deltaic deposits with associated beach and nearshore deposits that formed some forty to fifty million years ago near the margin of ancient Lake Uinta. The Sunnyside delta complex is interpreted to be seventy-five percent fluvial dominated and twentyfive percent wave dominated. The Sunnyside delta complex has been divided into three separate areas that include the Bruin Point, Dry Canyon and Whitmore Canyon subdeltas as seen on the Tar Sand Isopach Map. The Bruin Point subdelta contains about seventy percent of the mineable tar sands within eleven separate zones and is located in the southern (Amoco-Kaiser Tract) area. These bituminous sandstone deposits are largely confined to the Douglas Creek Member or delta facies with its characteristic red shales. The Amoco data base within the Bruin Point subdelta contains 5551 feet of field measured geological sections and 17,726 feet of deep vertical cores drilling with an average drilled depth per hole of 1108 feet. The adjacent Dry canyon subdelta contains about twenty-five percent of the mineable tar sands within seven separate zones and is located in the northern (Hydrocarbon Lease) area. These bituminous sandstone deposits are largely confined to the Garden Gulch Member or shore facies with its characteristic green shales and limestones. The Amoco data base in the Dry Canyon subdelta contains 8,999 feet of field measured geological sections and 10, 471 feet of deep vertical cored drilling with an average drilled depth per hole of 616 feet. The topographically isolated Whitmore Canyon subdelta contains about five percent of the mineable tar sands and is within the northwest area. These bituminous sandstone deposits are mainly confined to the Garden Gulch Member, but no specific data base is available for the Whitmore Canyon subdelta. 6. The mining aspects of the tar sands can be separated in a southern (Amoco-Kaiser Tract) area located in the Bruin Point subdelta and a northern (Hydrocarbon Lease) area located in the Dry Canyon subdelta. As seen on the various geologic sections the majority of the tar sands exist within a thick mineralized zone between the top and bottom of the principal tar sands. Within the southern area the depth to the top of the principal tar sands averages almost 500 feet; the thickness of the mineralized zone averages about 600 feet; and the saturated or pay zones total about 320 feet. Within the northern area the depth to the top of the principal tar sands averages about 110 feet; the thickness of the mineralized zone averages about 440 feet; and the saturated or pay zones total about 200 feet. The tar sand deposits in the southern area contain about 4.5 times more overburden than the northern area. The ratio of the mineralized zone to the pay zone is about 1.9:1 for the southern area and about 2.2:1 for the northern area. |
