Figures 1-4 

	Figure 1. Location of Covenant oil feld, uplifts, and selected thrust systems in the central Utah thrust belt. Numbers and sawteeth are on the hanging wall of the corresponding thrust system. Colored (light orange) area shows present and potential extent of the Navajo Sandstone Hingeline play in the central Utah thrust belt.
	Figure 2. Surface geology, Covenant field area, Sevier County, Utah.
	Figure 3. Stratigraphic column, central Utah thrust belt.
	Figure 4. Location of the Cordilleran Thrust Belt including the Montana “Disturbed” Belt, Utah-Wyoming-Idaho Salient, and Utah “Hingeline.”

 

Summary 

The central Utah thrust belt, or “Hingeline,” has seen cycles of petroleum exploration for the past 50 years because explorationists viewed the geology as a natural extension of productive thrust belt-style structures in northern Utah and southwestern Wyoming. Early unsuccessful efforts tested anticlines identified from surface mapping and seismic reflection data. The lack of a Cretaceous source seemingly was to blame for these failures. The 2004 discovery of Covenant oil field proved that this region contains the right components (trap, reservoir, seal, source, and migration history) for large accumulations of oil. To date, 10 producing wells and one dry hole have been drilled from two surface pads. Covenant has produced over 3 million bbls of oil and no gas; the field averages 5500 BOPD from the Jurassic Navajo Sandstone. The OOIP is estimated at 100 million bbls; the estimated recovery factor is 40%.  

The Covenant trap is an elongate, symmetric, northeast-trending, fault-propagation anticline formed during the Sevier orogeny (Late Jurassic-Early Tertiary), with nearly 800 ft (240 m) of structural closure. The structure formed above a series of splay thrusts in a passive roof duplex along the “blind” Gunnison-Salina thrust and west of a frontal triangle zone within the Jurassic Arapien Shale. The Jurassic Twin Creek Limestone and Navajo Sandstone are repeated due to an east-dipping back thrust detachment within the structure. This back-thrust forms a hanging wall cutoff along the west flank and north-plunging nose of the fold. Only the first Navajo (and possibly the Twin Creek) is productive. The eolian Navajo Sandstone reservoir is effectively sealed by mudstone and evaporites in the overlying Jurassic Twin Creek Limestone and Arapien Shale. Oil analysis indicates a probable Mississippian source – oil derived and migrated from rocks within the Hingeline region.  

Cores from the Navajo Sandstone display a variety of eolian lithofacies (dune, interdune, lake/playa, fluvial/wadi), fracturing, and minor faults which, in combina­tion, create reservoir heterogeneity. Res­ervoir sandstone is 97% frosted quartz grains (bimodal grain size), with some quartz overgrowths and illite. The net reservoir thickness is 424 ft (129 m) over a 960 acres (390 ha) area. Porosity averages 12%; permeability is ≤100 mD. The drive mechanism is a strong water drive; water saturation is 38%. A thorough understanding of all the components that created Covenant field will determine whether it is a harbinger of additional, large oil discoveries in this vast, under-explored region.

 

General Overview

(Figures 5-8) 

	Figure 5. Typical geophysical well log of the Jurassic Navajo Sandstone, Kings Meadow Ranches No. 17-1, discovery well, Covenant field.
	Figure 6. Typical geophysical well log of the Jurassic Twin Creek, Kings Meadow Ranches No. 17-1, discovery well, Covenant field.
	Figure 7. Reservoir seals: Jurassic Arapien Shale. Arapien Shale exposed in Salina Canyon (north of field); inset photo of salt core from Redmond quarry in the Arapien, north of the town of Salina.
	Figure 8. Historical monthly oil and water production, Covenant field.

 

Discovery Well 

Wolverine Gas & Oil Corporation

Kings Meadow Ranches No. 17-1

SENW Sec. 17, T.23S., R.1W, Sevier County, Utah

TD – 9382 ft

Completed – November 3, 2004

Producing reservoir – Jurassic Navajo Sandstone

IPF – 708 BOPD, 1 MCFGPD, 20 BWPD

 

Reservoir Data 

Productive area – 960 acres

Gross pay – 487 ft

Net pay – 424 ft

Net to gross – 0.87

Hydrocarbon column – 450 ft

Average porosity – 12%

Permeability – up to 300 mD

Water saturation – 38%

Water resistivity – 0.279

Ohm-m @ 77^oF, 26,035 TDS

BHT – 188^oF

Type of drive – strong water drive

Initial reservoir pressure – 2630 psi

 

Production and Reserves 

Producing wells – 10

Dry holes – 1

Abandoned producers – none

Monthly production (November, 2006) – 166,036 BO & 49,810 BW

Cumulative production (as of December 1, 2006) - 2,938,869 BO & 527,076 BW

OOIP – 100 million bbls

Estimated recovery factor – 40%

 

Structural Geology

(Figures 9-10) 

	Figure 9. Northwest-southeast structural cross section, Covenant field.
	Figure 10. Structural contour map, top of Navajo Sandstone, Covenant field.

 

Covenant Field Reservoir: Eolian Jurassic Navajo Sandstone

(Figures 11-22) 

	Figure 11. Regional Isopach Map of the Navajo/Nugget Sandstone. Paleowind generally from the north and northwest is shown by arrows. Contours are in feet.
	Figure 12. Modern analog – Little Sahara dune field, west-central Utah. Inset: Outcrop analog – Jurassic Navajo Sandstone, San Rafael Swell, east-central Utah.
	Figure 13. Average porosity for Upper Navajo lithofacies.
	Figure 14. Permeability for Upper Navajo lithofacies.
	Figure 15. Permeability vs. porosity cross plot by lithofacies, Upper Navajo.
	Figure 16. Core photos of lithofacies in Upper Navajo of the Federal No. 17-3 well.
	Figure 17. Typical geophysical well log of the cored section of Jurassic Navajo Sandstone, Federal No. 17-3 well.
	Figure 18. Core photos of lithofacies in Lower Navajo of the Federal No. 17-3 well.
	Figure 19. Average porosity for Lower Navajo lithofacies.
	Figure 20. Permeability for Lower Navajo lithofacies.
	Figure 21. Permeability vs. porosity cross plot by lithofacies, Lower Navajo.
	Figure 22. Representative photomicrographs and SEM images. Photomicrograph (plane light) and SEM image from the upper unit of the Navajo Sandstone showing typical well-sorted, subangular to subrounded quartz sand and silt. Note a few fractured and corroded K-feldspar grains are present. Blue space on photomicrograph is intergranular porosity. Federal No. 17-2 well, 6129 ft, porosity = 8.1%, permeability = 17.9 mD. Photomicrograph (plane light) and SEM image from the lower unit of the Navajo Sandstone showing bimodal distribution of subangular to subrounded quartz sand and silt. Blue space on photomicrograph is intergranular porosity. Federal No. 17-3 well, 6773 ft, porosity = 14.8%, permeability = 149 mD

 

Navajo Sandstone Lithofacies Recognized in Core from the Federal No. 17-3 Well 

T – Thick: dune deposits containing the large-scale, trough, planar, or wedge-planar cross-beds (35 to 40°) commonly recognized as classical eolian dune features. Very well to well-sorted, dune and avalanche deposits. Sand layers greater than 0.5 cm thick in core. The brink to the toe of the dune slipface consists of thin, graded, tabular grainfall laminae (rarely preserved in the core) and thick, subgraded, avalanche laminae. The “thick” classification is correlated to avalanche deposits. Porosity ranging from 5 to 15%, and permeabilties typically from 7 to 300 mD.

TC – Thin Continuous: sand layer continuously bedded, trough, planar, or wedge-planar cross-beds less inclined than the thick lithofacies (20 to 35°), and less than 0.5 cm thick in core. Moderately well to poorly sorted with more clay cementation than the “TD” lithofacies. The TC lithofacies can occur within the thick and Thin Discontinuous lithofacies making the TC lithofacies a transitional phase. All porosities are under 10% and permeabilites range from 1 to 30 mD

TD – Thin Discontinuous: flat lying bedding less than 0.5 cm thick in core containing wind ripples, and some cross-bedding (0 to 20°). Moderate­ly to poorly sorted with greater carbonate cement than TC layer. Thin discontinuous tightly packed, reworked ripple strata are representative of dune toe lithofacies. Low porosities and permeabilites are characteristic.

WBH – Interdunal: low-angle to horizontal laminae or distorted bedding consisting of very fine to fine-grained, thin, poorly sorted sandstone, siltstone, and shale dominated by carbonate cement. Beds may contain wind ripples or fluvial characteristics (scour). Very low porosities and permeabilities. Interdunal fluvial characteristics indicate sheet flow or flooding events in a fluvial/wadi while other deposits suggest wet, playa or lacustrine conditions.

M – Massive: homogenized sandstone layers showing no distinct sedimentary structures or laminations. This lithofacies probably formed by water-saturated sand.

FB – Fault Breccia: Breccia resulting from a fault and fracture zones running through the core of the Federal No. 17-3 well.

 

Petrography 

Lithology – very fine- to medium-grained (1/16 mm to ½ mm), quartz sandstone; 97%, white or clear quartz grains with varying amounts of K-feldspar.

Sand Grains – subangular to subrounded, very well to well-sorted, usually frosted.

Pore Types – primary intergranular, fracture.

Grain Density – 2.651 g/cm³

Diagenesis – minor overgrowths of quartz; some authigenic clay mineralization has occurred in the form of grain-coating, pore-bridging, and fibrous illite; some ferroan (?) dolomite and fractured, corroded K-feldspar are also present.

 

Oil Characteristics

(Figures 23-24) 

Figure 23. Stable carbon-13 isotope ratios for saturated vs. aromatic hydrocarbons from Covenant field oil and Cretaceous and Permian oils. Units on both axes of the graph depict the carbon isotopes measured in the oil versus the Pee Dee Belemnite (PDB) standard in parts per thousand; a negative value implies the oil sample is depleted in the heavy isotope relative to the standard. Data sources: 1=Sprinkel et al., 1997; 2=Lillis et al., 2003; 3=Baseline DGSI, 2005. CV= Canonical value (Sofer, 1984).

Figure 24. Oil sample from Kings Meadow Ranches No. 17-1 well.

 

Characteristics 

Oil gravity – 40.5º API

Color – dark brown

Viscosity – 4.0 centistokes @ 77ºF

Pour point – 2.2ºF

Sulfur – 0.48%

Nitrogen – 474 parts per million

Stable carbon-13 isotopes – -29.4‰ (saturated) and -29.0‰ (aromatic) hydrocarbons

Pristane/phytane ratio – 0.96

 

Source Rocks

(Figures 25-26) 

	Figure 25. Location of the Mississippian Delle Phosphatic Member present in the Deseret Limestone and other Mississippian formation.
	Figure 26. Location and thickness of the Manning Canyon Shale and correlative formations .

 

What’sNext?

(Figures 27-28) 

	Figure 27. Potential drilling targets: Schematic east-west structural cross section through Sevier Valley, Utah.
	Figure 28. Central Utah Thrust Belt play area and exploration activity.

 

References 

Baseline DGSI, 2005, Basic crude oil characteristics and biomarker analysis from the Kings Meadow Ranches No. 17-1 well, Covenant field, Sevier County, Utah: Utah Geological Survey Open-file Report 467, 15 p.

Gibson, R.I. 1987, Basement tectonic controls on structural style of the Laramide thrust belt interpreted from gravy and magnetic data, in Miller, W.R., ed., The thrust belt revisited: Wyoming Geological Association 38^th Field Conference Guidebook, p. 27-35.

Hamblin, W.K., 2004, Beyond the visible landscape – aerial panoramas of Utah’geology: Brigham Young University, Department of Geology, p. 232-233.

Hintze, L.F., 1980, Geologic map of Utah: Utah Geological Survey Map M-A-1, 2 sheets, scale 1:500,000.

Hintze, L.F., 1993, Geological history: Brigham young University Geology Studies Special Publication 7, 202 p.

Hintze, L.F. Willis, G.C., Laes, D.Y.M., Sprnkel, D.A., and Brown, K.D., 2000, Digital geologic map of Ytah: Utah Geological Survey Map 179 DM, 17 p. scale 1:500,000.

Kocurek, G., and Dott, R.H., Jr., 1983, Jurassic paleogeography and paleoclimate of the central and southern Rocky Mountains region, in Reynolds, M.W., and Dolly, E.D., eds., Symposium on Mesozoic paleogeography of west-central U.S.: SEPM Rocky Section, p. 101-116.

Lillis, P.G., Warden, Augusta, and King, J.D., 2003, Petroleum systems of the Uinta and Piceance basins – geochemical characteristics of oil types, in Petroleum systems and geologic assessment of oil and gas in the Uinta-Piceance province, Utah and Colorado: U.S. Geological Survey Digital Data Series DDS-69-B, Chapter 3, 25 p.

Moyle, Richard W., 1958, Paleoecology of the Manning Canyon Shale in central Utah: Brigham Young University Research Studies, v. 5, no. 7, 86 p., 7 plates.

Peterson, J.A., 2001, updated 2003, Carboniferous-Permian (late Paleozoic) hydrocarbon system, Rocky Mountains and Great Basin U.S. region—major historic exploration objective: Rocky Mountain Association of Geologists Open-field Report, 54 p.

Picard, M.D., 1975, Facies, petrography and petroleum potential of Nugget Sandstone (Jurassic), southwestern Wyoming and northeastern Utah, in Bolyard, D.W., ed., Symposium on deep drilling frontiers of the central Rocky Mountains: Rocky Mountain Association of Geologists Guidebook, p. 109-127.

Sandberg, C.A., and Gutschick, R.C. 1984, Distribution, microfauna, and source-rock potential of Mississippian Delle Phosphatic Member of Woodman Formation and equivalents, Utah and adjacent states, in Woodward, Jane, Meissner, F.F., and Clayton, J.L., eds., Hydrocarbon source rocks of the greater Rocky Mountain region: Rocky Mountain Association of Geologists Guidebook, p. 135-178.

Schelling , D.D., Strickland, D., Johnson, K.R., Vrona, J.P., Wavrek, D.A., and Reuter, J., 2005, Structural architecture and evolution of the central Utah thrust belt – Implications for hydrocarbon exploration (abs.): AAPG Annual Convention Official Program with Abstracts, v. 17, non-paginated.

Sofer, Zvi, 1984, Stable carbon isotope compositions of crude oils – Application to source depositional environments and petroleum alteration: AAPG Annual Convention Official Program with Abstracts, v. 6, p. A110.

Sprinkel, D.A., and Chidsey, T.C., Jr., 1993, Jurassic Twin Creek Limestone, in Hjellming, C.A., ed., Atlas of major Rocky Mountain gas reservoirs: New Mexico Bureau of Mines and Mineral Resources, p. 76.

Utah Division of Oil, Gas and Mining, 2006, Oil and gas production report, December: Online (http://ogm.utah.gov/oilgas/PUBLICATIONS/Reports/PROD_book_list.htm), accessed April 19, 2007.

Villien, A., and Kligfield, R.M., 1986, Thrusting and synorogenic sedimentation in central Utah, in Peterson, J.A., ed., Paleotectonics and sedimentation in the Rocky Mountain region: AAPG Memoir 41, p. 281-306.

 

Acknowledgments 

Funding for this ongoing research was provided, in part, under the Preferred Upstream Management Program of the U.S. Department of Energy, National Energy Technology Laboratory, Tulsa, Oklahoma, contract number DE-FC26-02NT15133. Support was also provided by the Utah Geological Survey (UGS) and Wolverine Gas & Oil Corp (WGO).  

Field cores were described by L.F. Krystinik, geologic consultant. Jake DeHamer, WGO, interpreted core petrophysical data. The poster design was by Liz Paton of the UGS. James Parker, Liz Paton, Sharon Wakefield, and Cheryl Gustin of the UGS prepared the figures; Brad Wolverton of the UGS Core Research Center assisted with core photography.