Covenant field

Figure 1 a) Inset map of the western United States showing the location of Utah. (b) Shaded relief map of Utah showing the location of the overthrust belt of northeastern Utah and southwestern Wyoming and the Covenant oil field, including tectonic elements. SR = San Rafael swell; KU = Kaibab uplift; MU = Monument uplift; WF = Waterpocket fold; A = Absaroka thrust fault. (c) Covenant field locality map of central Utah. From Parry, et. al

The Covenant Field is an oil field located in Sevier County, Utah. The field was discovered in 2004 by Wolverine Oil and Gas, in the Kings Meadow Ranches #17-1 well when it encountered oil in the Navajo Formation. Credits for the geologic ideas behind the discovery have been attributed to Dr. Douglas K. Strickland. The work leading to this discovery is has been summarized by Strickland in several presentations at AAPG conferences.

Structure

Figure 2 Generalized stratigraphic column of rock units the Covenant field area. The Lower Jurassic Navajo Sandstone is the reservoir, while the overlying Middle Jurassic Twin Peaks Limestone and Arapien Shale form the cap rocks or seal for the field. From Parry, et. al.

Figure 3 A NW-SE trending cross section showing the Covenant oil field structure, Paxton and Gunnison-Salina thrust, and normal faults bounding Sevier Valley. Note that OWC = oil-water contact for the covenant field. See Figure 2 for the key to the geologic symbols. From Parry, et. al.

The Covenant field is located in the central Utah thrust belt. Chidsey, et al. describe the Covenant field trap as an “elongate, symmetric, northeast-trending, fault-propagation/fault-bend anticline with nearly 800 feet (270m) of structural closure with a 450-foot (150M) oil column. The oil-charged Navajo reservoir covers about 960 acres.” The structure is related to movement along the Gunnison-Salina thrust and Paxton thrust fault and part of the larger Utah thrust belt province, this is outlined in greater detail by Chidsey et al.

Reservoir

The primary (as of 2007) reservoir in the Covenant Field is the Navajo Sandstone Early Jurassic (Toarcian) eolian sandstone. Parry, Chan, and Nash outlined diagenetic charchteristics of the Navajo Sandstone from cores in the Covenant field. As of April 2015 the field had 24 active wells, and had produced a cumulative 21,443,660 barrels of oil.

Table 1 Covenant Oil Field Reservoir Characteristics

Structural closure, 800 ft (270 m); oil column, 450 ft (150 m)
Reservoir depth, 6356 ft (1937 m) true vertical depth; subsea level depth, −94 ft (−29 m)
Oil-water contact, −603 ft (−184 m)
Reservoir temperature, 87°C (188°F); reservoir pressure, 2360 psi (18,134 kPa, 181 bar)
Average water saturation, 38%
0.48% S, d13C = −29.4 to −29.0‰
Structure: backthrust on the Gunnison-Salina thrust fault (Campanian to Paleocene)
Source rocks: Carboniferous; migration: Cretaceous to early Tertiary
Water Chemistry
Ca	428 mg/l	HCO–3	518
Mg	41	SO4	3000
Na	10,080	Cl	14,100
K	220	pH	6.45
Fe	12	Specific gravity	1.0208
SiO2	46	Total dissolved solids	28,400

Significance

The significance of the Covenant discovery, summarized by Chidsey, is that it proved that the central Utah thrust belt contained the right components of trap, reservoir, seal, source and migration history for large accumulations of oil to occur. In reflecting on the exploration work leading to its discovery Strickland noted that the Covenant field disproved many aspects of conventional wisdom as to the exploration potential of the region.

Still of Strickland giving his talk on the discovery of the Covenant field in 2009. See full video here

Related reading

• Brown, D., 2008, Tricky Geology Is Utah Hallmark: AAPG Explorer
• Hartwick, E. E., 2010, Eolian Architecture of Sandstone Reservoirs in the Covenant Field, Sevier County, Utah
• Strickland, D., 2009, Conventional Wisdom: A Different Approach Exploration in the Central Utah Thrust Belt

oil-water contact