Lithofacies
Prediction and Reservoir Quality Evaluation
Using Laboratory-Measured Physical Properties in the Pennsylvanian Mixed System
of the Paradox Basin, SE Utah
Christophe D. Nussbaumer, Eric Davaud, Gregor P. Eberli, G.
Michael Grammer, and Marie-Claire Bernet-Rollande
The various lithofacies
of Pennsylvanian siliciclastic/carbonate cycles on
the Paradox shelf and basin display characteristic
petrophysical
signatures.
Utilization of these
petrophysical
facies in combination with vertical stacking
patterns observed in the cycles provides a powerful tool to enhance the
predictability of
lithofacies
and reservoir characteristics from log data.
Ultrasonic velocities (P- and S-waves), permeability, porosity and density
values of 356 plugs were used to define the petrophysical
facies of nine
lithofacies
. Despite a large scatter in the data due to multiple subtle facies
variations, each
lithofacies
yielded a characteristic
petrophysical
signature.
The most significant distinction is seen between siliciclastics, i.e., quartz
sandstones (low grain density, low porosity, low P- and high S-wave velocity),
and carbonates (higher grain density, variable porosity, high P- and relatively
low 5-wave velocity). The
petrophysical
properties (porosity, pore-type,
permeability and velocities) also allow for the distinction between the two
carbonate reservoirs, phylloid algal facies and ooid grainstones, and between
the reservoirs and surrou ding nonreservoir carbonates.
This calibration of petrophysical
facies to
lithofacies
provides a powerful
tool to better interpret log data. For example, the admixture of quartz in the
bottom of the depositional cycle is recorded in the sonic logs by a decreased
velocity which helps distinguish individual cycles. In addition, acoustic
response within the carbonate portions of the cycles indicates variations in
porosity and, thus, reservoir heterogeneities. Furthermore, the measured rock
properties combined with outcrop geometries can be used as a foundation for
seismic and fluid flow modeling.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California