M. A. Gutierrez, J. Dvorkin, and A. Nur
Rock Physics
Laboratory,
Geophysics Department, Stanford University, Stanford, CA
ABSTRACT: Stratigraphy-Guided Rock-Physics
Reservoir Characterization
Depositional and diagenetic heterogeneities
compartmentalize fluvial reservoirs into flow units of
variable lateral and horizontal extent. These heterogeneities
prevent efficient drainage and sweep of reservoirs and are
frequently bound up with the facies architecture inherited
from the original depositional system. These reservoir
heterogeneities are among the principal causes of the very
low recovery in numerous gas and oil fields around the
world. To date, there has been little work on developing
specific techniques for reservoir characterization in fluvial
sedimentary settings, based on rock physics
analysis and 3-
D seismology; moreover, much of the work done in seismic
stratigraphy, particularly in marine sedimentary
environments, has focused on use of 2-D seismic data. The
problem of recovery efficiency in heterogeneous reservoirs is
of general significance because the ancient fluvial oil deposits
have considerable economic importance worldwide
Traditional seismic reservoir characterization puts emphasis
on finding the geological meaning of reflection data and/or
mathematical attributes thereof (e.g., seismic amplitude).
Geostatistics is often used to relate such attributes to
reservoir physical properties. However, these techniques are
often unable to deliver an accurate reservoir property
description because they do not take advantage of
deterministic physical links between seismic and reservoir
properties. In order to determine consistent relationships
among type of deposits, flow units, rock properties, and
petrophysical properties, a rock
physics
and seismic
characterization of reservoir heterogeneities is carried out in
this paper. Described here is a rock
physics
model for
relating the elastic reservoir properties to porosity,
mineralogy, pore fluid, and differential pressure, with the
stratigraphic framework used as a constraint to select the
relevant data subsets. The purpose of this model is to: (a)
generalize the relations observed in well log and core data, (b)
find the ranges of applicability of these relations, and (c)
separate the effects of porosity from those of pore fluid on
seismic properties. Finally, a new methodology is defined
for seismic mapping of the internal architecture of fluvial
sandstone reservoirs and the spatial distributions of
petrophysical properties and their flow units, that combines
core and well-log rock
physics
analysis with the stratigraphic
interpretation of 3-D surface seismic.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado