Circle Cliffs Research Articles

A comparison of fluidized bed pyrolysis of oil sand from Utah, USA, and Alberta, Canada

Characterization and thermal pyrolysis of oil sand was conducted. The experiment was performed on Circle Cliffs, Utah, U.S.A. and the results were compared with the data from Alberta, Canada. The reaction character identified by TGA was dual mode of vaporization of light hydrocarbon and thermal cracking of high molecular hydrocarbon. The pyrolysis experiment was performed in a 2 kg/h capacity fluidized bed externally heated by electricity. The process variables investigated were a temperature range of 723-923 K, fluidization gas velocity of 1.5-2 times of the minimum fluidization velocity, solid retention time of 15-30 minutes, and average particle size of 435 microns. The results of TGA and elemental analysis of bitumen provided necessary information regarding maximum liquid yield from the pyrolysis prior to pyrolysis experiment. The oil yield was maximum at 823 K. The yield of liquid was not exceeding the weight percent of maltenes in original bitumen. The optimum reaction condition should be fast vaporization of light hydrocarbon and minimizing thermal cracking of high molecular hydrocarbon. To maximize the liquid yield, fast heating and vaporization of oil sand bitumen and then the rapid removal of the vaporized product from the heating zone is recommended, i.e., operation in a fluidized bed reactor.

Late Cretaceous–early Tertiary Laramide deformation of the northern Colorado Plateau, Utah and Colorado

The structure of the northern Colorado Plateau is dominated by a series of highly asymmetrical, presumably fault-cored anticlines: the Kaibab, Circle Cliffs, Miners Mountain, San Rafael Swell, Monument, and Uncompahgre uplifts. In map view, they are irregularly distributed with widely varying sizes and orientations. In Permian through Jurassic rocks, interpretations of outcrop-scale structures, including jointed Eshelby inclusions, stylolites, en échelon vein arrays, deformation bands and meso-scale faults, show principal stress directions that are consistently oriented within each uplift, but vary considerably between uplifts. In general, the results indicate that there are two groups of uplifts, one of which shows evidence of NE–SW-directed compressive stress, and another which shows evidence of NW–SE-contraction. Because deformation in the sedimentary cover is forced by differential movement of basement fault blocks, cover stress patterns may be interpreted as basement strain patterns. These results are similar to the kinematic interpretations of Kelley and Clinton (1960) and highlight the importance of oblique slip. Finally, examination of structural contours allows the interpretation of basement strain magnitudes and indicates that the major faults are not interconnected.

Conjugate Riedel deformation band shear zones

Our investigations have disclosed that individual Riedel shear zones may organize themselves into broadly distributed though rigorously oriented intraformational conjugate systems which may form without relationship to, or dependence upon, an underlying basement fault zone. The Riedel shear zones we mapped are zones of deformation bands, which developed as the preferred deformation mechanism in porous Navajo Sandstone (Jurassic). In the Cottonwood area, located at the northern end of the Kaibab Uplift, a conjugate normal Riedel deformation band shear system developed during the Laramide in the uppermost Navajo Sandstone on the outer arc of the upper hinge zone of the East Kaibab monocline. In the Sheets Gulch area, located at the northern end of the Waterpocket Fold, a conjugate strike-slip Riedel deformation band shear system developed during the Laramide in upper Navajo Sandstone within an imperfect transfer zone between the northeast-vergent Circle Cliffs Uplift and the southwest-vergent Miners Mountain Uplift. Within both the Cottonwood and Sheets Gulch areas there are tens to hundreds of Riedel shear zones, the largest of which are up to hundreds of meters in trace length. In classic Riedel fashion, the synthetic R-shears within each Riedel shear zone depart by ∼15° from the zone as a whole and are arranged in an en échelon, overstepping geometry. The antithetic R′-shears depart by ∼75° from the Riedel shear zones of which they are a part, and are especially abundant in transfer zones where they create hard linkages between overstepping R-shears. At both localities the Riedel shear zones occur in two sets that intersect at ∼60°. The Riedel shear geometry is self-similar from the scale of hand samples (and thin sections) where offsets are measured in centimeters (or millimeters), to the map scale where displacements are measured in meters. Because of the small amount of deformation which had to be accommodated in each of the two study areas, and the limits imposed by the strain-hardening nature of deformation banding, we may be seeing a rare snapshot that records an image of early, arrested fault-system development in relatively homogeneous, porous sandstone. The literature on classic Riedel shear zones postulates that displacement and shear along Riedel shears brings about a localized reorientation of stress. This interpretation can be tested and confirmed, using the geometry and kinematics of conjugate Riedel systems. Detailed understanding of the total nested geometric characteristics of the conjugate Riedel deformation band shear zone systems also provides insight regarding controls on reservoir-scale fluid flow. The low permeability of the deformation band shear zones tends to compartmentalize the Navajo Sandstone into chambers along which fluid flow is channeled. The geometry and spacing of the deformation band patterns controls shapes and sizes of the compartments, which in these examples tend to be long, polyhedral, porous chambers marked by either diamond- or rhombic-shaped cross-sections.

VISCOSITY OF BITUMEN-CRUMB RUBBER BLEND (NEW PAVING MATERIAL)

ABSTRACT The feasibility of blending scrap tire rubber with Asphalt Ridge and Circle Cliffs (Utah, USA) tar sand bitumens was studied. Viscosity of the blended mixtures was analyzed as a function of composition, and coprocessing variables including processing temperature and time. Coprocessing of tar sand bitumens with crumb rubber at elevated temperatures has been shown to increase the viscosity of the bitumens with the exception of the bitumen-rubber sample prepared at 380°C. Optimum viscosity behavior was exhibited for an oil-extended bitumen blended with crumb rubber at 200°C for 0.5 hours. The viscosity of the bitumen-rubber blend prepared under these conditions met ASTM specifications of a viscosity-graded AC-30 asphalt binder. Viscosity increase was most noticeable at low temperature, providing the benefit of high viscosity at pavement temperatures experienced during summer months without concession of processability at pavement construction temperatures. A difference in viscosity was observed between bitumen modified with whole-tire crumb and tread-rubber crumb, due to the compositional differences that exist between the two materials.

Precambrian Chuar Source Rock Play:  An Exploration Case History in Southern Utah

Source rock potential of the Upper Proterozoic Chuar Group, specifically the Walcott Member of the Kwagunt Formation, provides the basis for a petroleum play in southern Utah. Analyses of Chuar black shales from outcrops in the Grand Canyon show total organic carbon values of 3-9%, hydrogen indices up to 255, and maximum maturity within the oil window. Modeling indicates a potential 150 mi2 (400 km2) area with a minimum generative potential of 2700 MBO*. Chuar source rocks are proposed as one part of a petroleum system that includes reservoirs in the Cambrian Tapeats Sandstone and seal in the overlying Bright Angel Shale. Prospective structures include anticlines of Laramide age not drilled through the Tapeats interval. One such structure is the Circle Cliffs uplift, which exhibits an area under closure of 900 mi2 (2300 km2) at the top of the Devonian. In 1994, BHP Petroleum drilled the 28-1 Federal well on the Circle Cliffs structure. The well logged 142 ft (43 m) of Tapeats porosity (>7%) and flowed CO2 gas at rates up to 5.0 Mcf* per day. Analysis of bitumen in the reservoir indicated an earlier hydrocarbon charge and suggested a new oil type for the region.

Examination of Neumann's Equation-of-State for Interfacial Tensions

Advancing contact angles for water, glycerol, diiodomethane, and ethylene glycol on polytetrafluoroethylene, polyethylene, Asphalt Ridge bitumen, Circle Cliffs bitumen, Whiterocks bitumen resins, and Whiterocks bitumen asphaltenes were measured and the "surface tension" of these low energy solids was calculated using Neumann's equation-of-state. Also, the surface tension of several polymers and self-assembled monolayers was analyzed based on Neumann's approach and using advancing contact angle values reported in the literature. It is demonstrated that the equation-of-state for surface tension determination may only be used for systems with apolar liquids involving interactions of a physical nature. Reasonable surface tension values were obtained for polymers when advancing contact angles for diiodomethane were used in the calculations. Nevertheless, there appears to be an inconsistency in the surface tension values determined for self-assembled monolayers as calculated with the equation-of-state using contact angle data for different apolar liquids, diiodomethane and hexadecane.

Characterization of Circle Cliffs oil sands of Utah

In the continuing characterization studies of Utah oil sands, this article was focused on the Circle Cliffs deposits which occur in the southeastern region of Utah. The bitumen was separated from the oil sand using a toluene extraction method. The extracted bitumen was fractionated using the modified SARA method and its fractional composition was compared to the other bitumens obtained from the Uinta Basin deposits. This comparison indicated that Circle Cliffs bitumen was unique among the Utah oil sand bitumens, particularly with respect to the chemical composition of its resin fraction, but showed resemblance with the Canadian Athabasca bitumen in some features. The effect of resin composition on the bitumen viscosity is discussed. Mineralogical analysis was performed on the solids, which indicated relatively large proportions of carbonate and kaolinite minerals. The undesirable effect of these minerals in the modified hot-water processing of Circle Cliffs oil sands is briefly discussed.

Tectonic development of Upper Cretaceous to Eocene strata of southwestern Utah

Upper Cretaceous to Paleogene nonmarine sedimentary rocks of southwest Utah record Sevier foreland basin sedimentation, Laramide-style folding and intermontane sedimentation, and cessation of Laramide deformation. The formations that record this tectonic evolution are, from oldest to youngest, the Iron Springs, Kaiparowits, Canaan Peak, Grand Castle (informal name), Pine Hollow, and basal part of the Claron. The upper part of the Santonian to lower Campanian(?) Iron Springs Formation represents synorogenic, fluvial deposits derived from the Wah Wah and Blue Mountain thrust sheets of southwestern Utah. The middle to upper Campanian Kaiparowits and upper Campanian(?) to lower Paleocene Canaan Peak Formations are an upward-coarsening sequence derived from southeastern California and southern Nevada. Initial Laramide-style deformation occurred during latest Cretaceous or early Paleocene time, influencing the depositional pattern of the Canaan Peak fluvial system. The lower Paleocene Grand Castle formation represents an east- to southeast-flowing, braided-river system with the same source as the Iron Springs Formation (the Wah Wah and Blue Mountain thrust sheets). Conglomerate of Grand Castle onlaps the easternmost Sevier thrusts and is folded by Laramide structures. Although strata of the Grand Castle formation represent post-thrust and, in part, pre-Laramide deposition, initial development of a south-southwest-trending, Laramide-style upwarp controlled the geometry of the Grand Castle basin. The lower Paleocene to middle Eocene Pine Hollow Formation unconformably overlies post-Sevier conglomerates and records Laramide partitioning of the foreland basin. The Pine Hollow basin received sediment from both the west and northeast, and it is associated with development of the Johns Valley anticline and possibly the Circle Cliffs uplift. Small alluvial fans developed on the limbs of these structuresand graded laterally into playa mudflats. Fluvial, deltaic, and lacustrine deposits of the basal part of the Claron Formation are coeval with the Pine Hollow Formation, but they developed in a separate basin to the southwest. Lacustrine deposits of the Claron Formation overlap paleotopographic highs of the Pine Hollow basin and indicate cessation of Laramide deformation by middle Eocene time.

Basin tectonics and erg response

The alignment and distribution of facies in the major erg (eolian sand sea) deposits in the Permian and Jurassic systems on the Colorado Plateau show remarkable coincidence with modern tectonic elements. This indicates that subtle tectonic elements, precursors to the present ones, were coeval with ancient eolian deposition and controlled erg geometry and facies distribution. No other known controls or processes were capable of producing the observed patterns. Facies and architectural analysis of the Permian and Jurassic erg deposits define several major trends across the Colorado Plateau. The High Plateaus trend, parallel to and slightly east of the Wasatch line, is defined by a zone of thinning and facies change of several erg deposits. The Zuni trend lies along the Zuni lineament and is coincident with facies changes or erg margins of several units. The Colorado trend lies along the course of the modern Colorado River and a number of erg margins and several facies changes coincide with it. Most erg centers, as defined by facies and thickness, lay within paleobasins that include the Circle Cliffs trough, Holbrook, Black Mesa, and Blanding basins, and southern Cordilleran Miogeocline. Most erg deposits thin or pinch out across paleoarches, which include the Sedona, Monument, Emery and Defiance arches. Although the exact relation between the paleostructures and facies distribution is uncertain, it appears likely that some of the structural elements defined areas of greater and less sand accumulation. Areas of greater sand accumulation would be expected to be dominated by facies typical of erg centers and areas of lesser sand accumulation would be expected to be dominated by facies typical of the erg margin and eolian sand sheets. The structures may have also formed straight margins in aqueous environments such as rivers and marine coasts; straight, vertically stacked facies changes are commonly associated with erg margins in the stratigraphic record. Early post-depositional uplift of some arches may have defined straight, thin edges of some eolian sequences. The knowledge that subtle intrabasinal tectonic elements had an effect on eolian deposition can be used to reconstruct basin history; therefore, the mapping of eolian geometry and facies patterns can provide powerful information concerning the tectonic evolution of a sedimentary basin.

Characterization of Circle Cliffs tar sands: 2. Application of the e.p.r. technique to paramagnetic metal ions

In the second of a two-part investigation, the results of an e.p.r. study of the paramagnetic metal ions in the bitumen and mineral components of Circle Cliffs tar sand are reported. Analysis of a spectrum observed at g ≈ 2 in the bitumen component and assigned to V 4+ shows that vanadium originates in the vanadyl etioporphyrin complex. A computer simulation of a complex exhibiting characteristics of the Mn 2+ ion, which is observed in the mineral component at g ≈ 2, is shown to arise from manganese in dolomite. A broad feature at g ≈ 4 in the mineral spectrum is identified as Fe 3+ located at sites in kaolinite clay. Finally, a very broad band underlying the manganese spectrum at g ≈ 2 is tentatively identified as originating with amorphous iron oxides coating clay particles. The results demonstrate the utility of e.p.r. in not only identifying important metallic ions but also establishing the organic or inorganic complexes in which they occur.

Characterization of Circle Cliffs tar sands. 1. Application of the FT-i.r. technique to mineral matter

In the first of a two-part study of mineral matter associated with tar sands, results are presented from the characterization of samples from the Circle Cliffs and P.R. Spring deposits using FT-i.r. spectroscopy. Following the collection of data for a library of minerals associated with tar sand deposits, the procedures used in the analysis were tested on mineral mixtures of known composition. Illite, dolomite, kaolinite and quartz were measured in the Circle Cliffs sample, while the only minerals present in the P.R. Spring specimen were microline feldspar and quartz.

Jurassic Crustal Deformation in West-Central Part of Colorado Plateau: ABSTRACT

Although the Jurassic Period is commonly thought of as a time of tectonic quiescence, updated isopach maps and new sedimentologic information indicate that it was a time of notable crustal deformation on the Colorado Plateau. A significant change in structural style occurred in Middle Jurassic time, especially during the erosion interval that produced the J-3 unconformity. Prior to late Middle Jurassic time, the region had been tilted westward and structural troughs formed in the area of the present-day Circle Cliffs uplift and in the vicinity of the the Circle Cliffs and Black Mesa regions were uplifted and the nearby Henry and Kaiparowits regions began to be downwarped as troughs or basins. It cannot be determined if or how the present-day monoclines flexed during the Jurassic. However, the direction of structural tilt across these areas changed from west side down to east side down during the late Middle and early Late Jurassic. The Monument region, the largest and most persistent structural element in the region, changed from a structural bench to a positive structure in the early Late Jurassic. In most cases the positive structures subsided more slowly than adjacent downwarps. Two exceptions during the Late Jurassic are the Black Mesa and Emery uplifts. These are the only uplifts that actually rose above the level of sediment accumulation. Jurassic rocks are not known to contain significant hydrocarbon resources in this region, but their tectonic history may offer clues to the structural history of underlying Paleozoic strata, which are the primary hydrocarbon exploration targets. End_of_Article - Last_Page 859------------

Sedimentologic and Tectonic Control of Uranium Mineralization, Upper Triassic Chinle Formation, Southeastern Utah: ABSTRACT

Uranium deposits in the Upper Triassic Chinle Formation of the White Canyon, Capitol Reef, and Circle Cliffs areas occur in a succession of lithofacies that formed from sediments deposited under anoxic conditions. Anoxic conditions in the depositional environments of these lithofacies are indicated by the preservation of abundant organic matter and the drab (reduced) colors of the rocks. The coincidence of facies changes and the vertical sequence of rocks associated with isopach thicks suggests that certain depositional environments were localized by tectonic subsidence. Lake, marsh, and bog environments adjacent to anastomosing fluvial channel systems occur in synclinal areas that were actively subsiding during deposition. Deposition in these wetland environments, whic had high organic productivity, high water tables, and minimal clastic input, resulted in organic-rich rocks. The vertical sequence of lithofacies indicates that initially the rate of tectonic subsidence was greater than the rate of clastic sediment influx. Subsequently, as the rate of clastic influx exceeded the rate of subsidence, sedimentation on prograding deltas buried the wetland deposits with clastic sediments that also contained abundant detrital plant debris. The subaqueous decomposition of this organic matter produced anoxic conditions in the overlying deltaic sediments that protected underlying marsh and bog deposits from oxidizing meteoric waters. Preservation of the organic material incorporated in the bog and marsh deposits established the reducing chemical environment nece sary to precipitate uranium. Maintenance of this reducing environment also protected uranium deposits from later oxidation. Subsidence, concomitant with sedimentation, produced the hydrologic conditions conducive to plant production, accumulation, and preservation and established the reducing chemical conditions necessary to precipitate and preserve uranium. Identification of wetland environment sediments that accumulated in structurally controlled areas of subsidence is a useful guide for uranium exploration in the Chinle Formation. End_of_Article - Last_Page 936------------

Late Jurassic Tectonism on West Side of Colorado Plateau, Utah and Arizona: ABSTRACT

Detailed sedimentologic studies in south-central Utah and north-central Arizona indicate that several major basins and uplifts as well as many smaller folds within them were actively growing during deposition of the Salt Wash Member of the Morrison Formation. The region lies outside that part of the Colorado Plateau underlain by thick Pennsylvanian halite deposits so the structures are not related to salt deformation. Tectonic activity in the region is inferred from several types of sedimentologic features which include thickness variations, facies distribution, cross-bedding parameters, and bedding ratios. Distribution of the various features studied indicates the Emery, Circle Cliffs, Echo Cliffs-Kaibab, Cow Springs, and Monument uplifts, as well as the Henry and Kaipar wits basins, were active during the Late Jurassic. In addition, several anticlines and synclines that were active at the same time can be delineated in or near the Henry and Kaiparowits basins. The apparent absence of local angular unconformities in the Salt Wash near the positive structures suggests that most of the tectonic movements were the result of differential subsidence rather than uplift of the positive structures. It could not be determined if the San Rafael swell near the Emery uplift was active during Late Jurassic time. Also, the relationships are not entirely conclusive but suggest that the Cow Springs uplift may have extended southeast across Black Mesa and that downwarping may not have occurred there in the Late Jurassic. Late Jurassic folds have essentially the same northwest to north-northwest trend as many of the Laramide and possibly younger folds in the region although the older folds tend to be less sinuous. Vertical repetition of lacustrine strata, deposited under conditions especially sensitive to slight tectonic movements, suggest that the movements were episodic. Comparison of the present amount of structural relief with the Late Jurassic structural relief indicates that approximately 3 to 7% of the present-day relief between several of the major basins and uplifts can be attributed to tectonic movements during deposition of the Salt Wash. Thus, it is erroneous to assume that all of the structural deformation in the region occurred during or after the Laramide orogeny. End_of_Article - Last_Page 1351------------

Thermophysical characterization of oil sands. 2. Acoustic properties

Propagation characteristics of shear (S) and compressional (P) waves are investigated for oil sands from the Athabasca, P.R. Spring, N.W. Asphalt Ridge and Circle Cliffs deposits. These studies are oriented towards applications of acoustic techniques in characterization, diagnostics and control of in-situ extraction methods currently envisaged for oil sand bitumen. The magnitude of the temperature dependence of S and P wave velocities is directly related to the bitumen content of the oil sand. The origin of the pronounced changes in Sand P wave velocities (or travel times) in the temperature regions 24–200 °C and 425–500 °C is traced to the thermal decomposition of oil and sand bitumen. The S and P wave velocities generally decrease with increasing bitumen content. Other variables that are studied, such as moisture content and bulk density, have relatively minor effects on the magnitude of the measured S and P wave velocities.

Thermophysical characterization of oil sands. 1. Specific heats

Differential scanning calorimetry is used to measure the specific heats ( C p ) of oil sands selected from four major deposits in the US and Canada. The C p values are in the range 0.670–1.57 J g −1 K −1 for temperatures ranging from 100 to 350 °C. The temperature dependence of C p for N.W. Asphalt Ridge (94.5 m burial depth) and P.R. Springs oil sands is larger than for Circle Cliffs and N.W. Asphalt Ridge (158.5 m burial depth) oil sands. Oil sands from the Athabasca deposit have slightly lower C p values relative to other deposits. Specific heats of oil sand bitumen are always appreciably higher than those of the corresponding parent samples. Predictive equations, obtained from regression analyses of the experimental data, are presented, which allow computation of C p values for an oil sand at a given temperature.

Thermophysical characterization of oil sands: 3. Electrical properties

The electrical behavior of oil sand samples from the Athabasca, N. W. Asphalt Ridge, P. R. Spring, and Circle Cliffs deposits was studied in the frequency range 50 Hz – 103 MHz at ambient temperature and up to 550 °C. Anomalously high dielectric constants (ε′) were measured for these samples at low frequencies (<1 kHz) and at elevated temperatures (>200 °C). Accumulation of mobile charges at the phase boundaries in the oil sand matrix was probably responsible for this effect. These mobile charges were presumably created by thermal fragmentation of oil sand bitumen. The anomalous increase in the low-frequency (50 Hz – 1 MHz) ε′ values at temperatures above 150 °C was also traced to interfacial polarization effects. Dipole relaxation behavior was observed for the various samples at frequencies below ~1 kHz and in the temperature range 150–470 °C. Two distinct relaxation processes were identified. The low-temperature (150–400 °C) process had activation energies for dipole orientation ranging from 4.0 to 9.0 kJ/mol depending on the oil sand specimen. The second relaxation process, which occurred at temperatures above 400 °C, had significantly higher activation energies (30–34 kJ/mol). The occurrence of these dipole relaxation peaks may be relevant in the use of electrical techniques to map the location of pyrolysis zones in in situ oil sand retorts. Measurements on the Athabasca samples in the high-frequency range (1–103 MHz) revealed distinct changes in the dielectric parameters associated with the loss of water from the oil sand matrix. The electrical behavior of oil sands is represented in terms of an equivalent circuit model comprising discrete RC elements corresponding to various components in the oil sand matrix. Such a representation was found to aid in an assignment of the observed changes in the electrical properties with frequency and temperature to distinct physical or chemical processes occurring in the oil sand matrix.

Migration and Entrapment of Petroleum--Examples from Utah Oil-Impregnated Sandstone Deposits: ABSTRACT

Utah contains more than 50 deposits of oil-impregnated rock ranging in size from tiny patches to areas covering hundreds of square miles. These deposits are estimated to contain a total of 22.9 to 29.3 billion bbl of oil. The following deposits are discussed, with illustrations and samples displayed. (1) South margin of the Uinta basin (P. R. Spring, Hill Creek, and Sunnyside deposits)--complex of deltaic sands impregnated with oil which is migrating out of the Uinta basin. Entrapment is controlled by thickness, volume and permeability changes in the reservoir; buoyancy of oil; regional structure; and jointing. (2) Central Uinta basin (Chapita Wells and Pariette deposits)--oil migrating up vertical gilsonite veins and outward into adjacent porous fluvial channel sandstones. (3) North flank of Uinta basin (Tabiona deposit)--pale yellow, live oil seeping up vertical sandstone beds in a structurally complex area, migrating across an unconformity, and accumulating as a black in basal sandstone a ove the unconformity. (4) Central southeast region (Tar Sand Triangle and Circle Cliffs deposits)--giant fossil oil fields on flanks of major uplifts exposed by erosion. The Tar Sand Triangle with 12.5 to 16.0 billion bbl in place in the Permian White Rim Sandstone is the largest tar sand deposit in the United States. The Circle Cliffs deposit contains 1.3 billion bbl of oil in the middle (Torrey sandstone) member of the Moenkopi Formation (Triassic). At their present location, Utah's oil-impregnated rock deposits may still be migrating toward a trap or to seepage and dissipation. Some deposits are active seeps indicating untapped oil reservoirs at an unknown vertical and horizontal distance. End_of_Article - Last_Page 774------------

Major Petroleum-Impregnated Rock Deposits of Western Colorado Plateau: ABSTRACT

Petroleum-impregnated rock deposits occur widely in rocks of Permian to Tertiary age in the western Colorado Plateau of Arizona and Utah. Although over 60 occurrences and deposits have been recognized to date, only six, all in Utah, are estimated to contain over one billion bbl of petroleum in place. Two giant deposits occur in marine and marginal marine strata in the dissected plateau region of southeastern Utah. The largest of these, and the largest single known deposit in the United States, is the Tar Sand Triangle. It underlies approximately 225 sq mi (585 sq km), and is estimated to contain as much as 16 billion bbl of petroleum, principally in the White Rim Sandstone (Permian). The Circle Cliffs deposit contains approximately 1.3 billion bbl of petroleum in siltstone and sandstone of the Moenkopi Formation (Triassic). The deposit underlies an area of approximately 28 sq mi (73 sq km) on both sides of a breached anticline. Several similar, but smaller deposits occur in the Moenkopi Formation to the north, in the Capitol Reef anticline, and in the San Rafael uplift. The remaining giant deposits are located in the Uinta basin, and all contain petroleum which probably originated in the lacustrine Green River Formation (Eocene). These deposits include P. R. Spring, Hill Creek, Sunnyside, Asphalt Ridge, and Asphalt Ridge Northwest. The total amount of petroleum contained in these deposits in the Tar Sand Triangle and Uinta basin approaches a resource base of 29 billion bbl. The deposits are variable, and each offers a variety of technologic and economic challenges. End_of_Article - Last_Page 686------------

Petroliferous Lithosomes in the Moenkopi Formation, Southern Utah

Recent stratigraphic studies of the Triassic Moenkopi Formation suggest the possibility of important petroleum potential within the unit in southeastern and central Utah. Potential reservoir rocks include shoreline sandstone in the Black Dragon Member, carbonates in the Sin bad Limestone Member, and delta-front and delta-slope sandstone in the Torrey Member. Significant tar sand deposits have been mapped in the Moenkopi Formation in the San Rafael Swell and Circle Cliffs, and small oil and gas fields produce from the Moenkopi at the Grassy Trail and Last Chance fields respectively. These occurrences plus the large areas of bleached, nonred Moenkopi indicate that large amounts of hydrocarbons have moved through the formation. The most favorable source rocks for the Moenkopi hydrocarbons were probably the thick, dark, Paleozoic and Lower Triassic rocks west of the Cordilleran Hingeline (Wasatch Line). Thick Jurassic rocks deposited west of the Ancient Ephraim Fault may also have been important source rocks. Future successful exploration in the Moenkopi will involve locating an area where reservoir rocks and favorable structure coincide. Previous exploration involving surface structure has been rather disappointing, but recent exploration in the Rocky Mountain Region has indicated that many existing oil fields occur along major lineaments and their intersections. Major linear features are located throughout the area of study and may provide the most promising areas for future exploration.