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Throughout this area's geologic
history, the Hingeline has marked a pronounced boundary
between two different terrains. During Late Proterozoic to
Devonian time, it marked the boundary between a very thick
layer of sediments deposited in western Utah and a thin
sequence in eastern Utah. Later, the Hingeline coincided with
the eastern edge of a mountain belt that formed during the
Sevier Orogeny, a mountain-building period that took place
during Cretaceous to Tertiary time. Today it marks the general
boundary between the Basin and Range and the Colorado Plateau
physiographic provinces. Thrust faults and large anticlines
that formed during the Sevier Orogeny provide the trapping
mechanism for the Pineview oilfields.
Daniel Schelling, structural geologist and David Wavrek of
International Petroleum Systems gave specifics at the SPE
meeting. The seal is the middle Jurassic Arapian, a 5,500-ft
mudstone with halite, gypsum and anhydrite layers. These
layers are good reflectors, making seismic interpretation more
difficult. The reservoir is the lower Jurassic Navaho, a
1,200-ft aeolian sandstone. They consider the source rock to
be of Mississippian age whereas the previous paradigm was that
it was the Permian Phosphoria. The trap is described as large
scale fault bend fold.
The actual discovery was an early Christmas gift. On December
22, 2003 the operators hit the Navaho Sandstone at 5,800 ft
instead of the anticipated 7,200 ft. By December 24 they had
500 ft of oil shows and had established the NAV1 reservoir
with flow and correlation to the Rangely Weber Oil. The
petrophysics of the discovery well are gross pay 487 ft, net
pay 424 ft, average porosity 12 percent and water saturation |
38 percent. The permeability was reported as 100 mD, but
they were unable to comment on how much
natural fractures contribute to this permeability. Potential
reserves are estimated at 75-200 million barrels for this
1,600 acre field, and they are hoping for 50 percent oil
recovery. The finding costs were $5.5 million split among 10
partners. Estimated development costs for the field are $56
million.
Doug Strickland gave further information at
an RMAG luncheon meeting in Denver on June 3. Doug described
how Wolverine used the good dipmeter data from a Chevron well
drilled to 17,000 ft in 1981, and conventional seismic, to
determine that they could drill 1,500 ft higher on structure.
Drilling motors and modern mud systems kept the well on target
through the highly deformed and salt-rich Arapian shale. The
Navaho sandstone did not show up on seismic, so they had to
rely on the deepest salt layer in the Arapian as a marker.
Formation water is fresh with an Rw of 0.4-0.6. The reservoir
has a water drive and they expect to have a total of 12-15
wells on 160-acre spacing. Production is projected to reach
5,000 BOPD by August of 2005.
Wolverine has 500,000 acres under lease in central Utah and
has identified 25 drillable structures.
To summarize, a story of how patience and perseverance can pay
- in this case, 500 ft of pay.
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