The Jurassic Navajo Sandstone as a Partitioned (?) Subsurface Reservoir: Comparing Reservoir Characteristics and Facies Between San Rafael Swell Outcrop and Covenant Field Core, Utah
Morris, Thomas H.1, Ashley Hansen1, Stephanie Carney2, Craig
D. Morgan2, and Thomas C. Chidsey2
1Brigham Young University,
Provo, UT
2Utah Geological Survey, Salt Lake City, UT
Reservoir characterization and facies analysis of outcrop and
core from the Jurassic Navajo Sandstone in east-central Utah indicate
that impermeable barriers can divide the Navajo into upper and lower
flow units. In outcrop on the west flank of the San Rafael Swell, the
lower Navajo (50+ m) is heterogeneous and contains five different
interdune facies that are interbedded with dune facies. Average
porosity and permeability of interdune facies are relatively low and
their lateral extent is variable, ranging from tens to thousands of
meters. Thus, the lower part of the Navajo would contain numerous
baffles to fluid flow and serve as a lower quality reservoir in the
subsurface. The upper Navajo section (200 m) is dominated by dune
facies with relatively few interdune baffles, which are thin and
“leaky.” Hence, the upper Navajo should serve as a very high quality
reservoir. The lower and upper Navajo are separated by an algalinfluenced
interdune unit that has very low permeability (average of
0.265 mD) and extends for several kilometers. Thus, in an oil field
that has tight structural closure, this facies could act as a barrier to
fluid flow and partition the Navajo into two distinct flow units.
Core from the Covenant field can also be divided into lower and
upper Navajo units, which are both dominated by dune facies making
high quality subsurface reservoirs. Ten meters of apparently tidalinfluenced
mudrocks separate these units, creating a barrier to fluid
flow that potentially partitions the reservoir.
AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah