Assessment of Scale on Permeability
Estimates
in Late Cretaceous Reservoirs, Denver Basin, Colorado
This study addresses how reservoir-scale permeability
models
vary depending on the scale of investigation of the input
permeability
values.
A common practice in reservoir modeling is to directly use
permeability
measurements from core-plugs or probe permeametry in petrophysical modeling.
The petrophysical models may have varying grid sizes but are often 5-7 orders
of magnitude larger than scale of investigation (volume support) of the
permeability
measurement. This scale difference can produce unrealistic results
in the petrophysical model and may not be representative of the reservoir
heterogeneity.
To explore this issue, two stratigraphic intervals,
the Sussex (Terry) and Shannon (Hygiene) sandstones of the Denver Basin (within
Wattenberg and Spindle fields), were selected for permeability
analysis,
near-wellbore modeling for effective properties, and 3-D reservoir-scale
modeling. The stratigraphic units represent shoreline sandstones and exhibit
six common lithofacies.
Permeability
values by lithofacies (N=520 per core)
from four cores were measured using probe permeametry and used as inputs for
near-wellbore modeling to generate effective-
permeability
values using
flow-based upscaling. The effective-
permeability
values exhibit a narrower
distribution as compared to the original permeameter-scale values. Reservoir-scale,
three-dimensional models [1 mi2 (1.6 km2)] of lithofacies, porosity, and
permeability
for the Shannon and Sussex were constructed for an area in the
Spindle Field. Separate
permeability
models were generated using the original-
and effective-
permeability
values. Using porosity and
permeability
cutoffs
(>10% and >0.05md), the models were explored in terms of static
connectivity of reservoir-quality sandstone and show the differences in
connected volumes as a function of the input
permeability
values (original vs.
effective). The models show differences in static “reservoir”
connectivity as related to original- and effective-
permeability
that can be
significant in terms of properly representing reservoir heterogeneity. The
models illustrate the importance of scale of investigation when creating 3-D
reservoir models of petrophysical properties.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California