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Meyer, Thomas, Stephen R. Kneller, Robert McDermott, and Mark Longman, 2014, Geology of the Lance Pool, Pinedale field, in M. Longman, S. Kneller, T. Meyer, and M. Chapin, eds., Pinedale field: Case study of a giant tight Previous HitgasNext Hit sandstone reservoir: AAPG Memoir 107, p. 61116.

DOI:10.1306/13511889M1073631

4

Geology of the Lance Pool, Pinedale Field

Thomas Meyer

Santos Ltd., Adelaide, South Australia, Australia (e-mail: [email protected])

Stephen R. Kneller

Ultra Petroleum Corporation, Denver, Colorado, U.S.A. Retired

Robert McDermott

South Pass Resources, Inc., Edinboro, Pennsylvania, U.S.A. (e-mail: [email protected])

Mark Longman

QEP Resources, Inc., Denver Colorado, U.S.A. (e-mail: [email protected])

ABSTRACT

The Pinedale field, a giant Previous HitgasNext Hit and Previous HitgasNext Hit condensate field, is located in the northwest part of the Green River Basin in southwest Wyoming. This field has an estimated ultimate recovery (EUR) of 39 trillion cubic feet of Previous HitgasNext Hit equivalent (tcfe), making it the third largest Previous HitgasNext Hit field in the United States based on 2009 statistics from the U.S. Energy Information Administration. Additionally, the natural Previous HitgasNext Hit condensate production makes it the 49th largest oil field in the same study. Production is principally from overpressured, Previous HitgasNext Hit-saturated, tight Previous HitgasNext Hit sandstones and siltstones of the Lance Pool comprised of the Upper Cretaceous Upper Mesaverde interval, the Upper Cretaceous Lance Formation and the lowermost part of the lower Tertiary Wagon Wheel Formation.

The presence of natural Previous HitgasNext Hit in the Pinedale anticline area has been known for decades. The California Company drilled the first well within the current Pinedale field production limits in 1939 and encountered Previous HitgasNext Hit but completion attempts failed. Despite numerous wells drilled over the ensuing years, it was not until the late 1990s that the first commercial production was achieved in Pinedale field. This success was largely the result of improved multistage fracture stimulation techniques, which had been successful in nearby Jonah field's tight Previous HitgasNext Hit, low-permeability Lance Pool sandstones and siltstones.

Pinedale field is a complex accumulation and still has some disagreements as to its true nature. The trapping mechanism within the field has both stratigraphic and structural components and the reservoir has further been shaped in areas by natural fracturing. The field is coincident with the thrust-bounded Pinedale anticline, which is situated approximately 5 mi (8 km) west of the west edge of the Wind River Mountains, another thrust-fault-bounded feature. The Wyoming thrust belt is located approximately 30 mi (48 km) to the west. The town of Pinedale, Wyoming, is at the northeast end of the field. Jonah field, also a giant Previous HitgasNext Hit field producing from the interval equivalent to the Lance Pool in Pinedale, is adjacent to and just west of the southern limit of Pinedale field. The absolute field limits of Pinedale are still being defined, but the current field is about 30 mi long (48 km) and up to 5 mi wide (8 km) in places.

Producing rocks in the Lance Pool mainly consist of alluvial plain deposits. The source sediments were Paleozoic and Mesozoic sedimentary rocks eroded from surrounding uplifts and deposited in a rapidly subsiding basin. The Lance Pool hydrocarbon-bearing sandstone, siltstone, and shale column locally exceeds 6000 ft (1829 m) in total thickness. The primary reservoirs in the interval are fluvial channel sandstones deposited by migrating rivers, which flowed generally from northwest to southeast across the depositional area. The resulting reservoir bodies are complex laterally and vertically stacked discontinuous multistory and single-story channel-fill and overbank deposits with as much as 1600 ft (488 m) of net productive sandstone and siltstone in the Lance Pool. Total drill depths range up to 15,000 ft (4572 m) subsurface. Average porosity in these Previous HitgasNext Hit-bearing sandstones is about 7% with just 0.005 mD (5 microdarcies) of permeability. The reservoir is overpressured from about 0.57 pounds per square inch per foot (psi/ft) at the top of the Lance Pool gradually increasing to 0.85 psi/ft near the base of the productive interval.

The source of the abundant Previous HitgasNext Hit in the Lance Pool at Pinedale field has been the subject of much discussion. The Lance Formation itself contains relatively little organic matter and has never been hotter than the oil-generation window. The top of the dry Previous HitgasNext Hit window occurs at a depth of about 15,000 ft (4572 m) in the Rock Springs Formation. The Upper Mesaverde interval has some carbonaceous shale layers and thin coals that were in the wet-Previous HitgasNext Hit window and could have generated a relatively small amount of Previous HitgasNext Hit. Isotopic analyses of the produced Previous HitgasNext Hit in the Lance Pool indicates higher thermal maturity (Ro >2%), which imply a source deeper than the deepest depth penetrated to date by drilling to the upper Hilliard Shale in the field. These potential deep source beds include the lower portions of the upper Cretaceous Hilliard Shale, and the lower Cretaceous Mowry Shale, possibly with a relatively minor contribution from coals in the lower part of the Upper Cretaceous Rock Springs Formation. Hydrocarbon generation and migration into the reservoir rocks of the Lance Pool at rates in excess of the rate of leak-off charged the section and resulted in the overpressured, Previous HitgasNext Hit-saturated reservoir.

To date more than 2000 wells have been drilled in the field with cumulative production through the end of 2011 at 3.3 trillion cubic feet (tcf) of natural Previous HitgasNext Hit and 25.4 million barrels (MMBLS) of Previous HitgasTop condensate.

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