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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Ambiguity and Sensitivity of Rock Properties under Different Reservoir Conditions
By
TraceSeis, Inc.
Houston, Texas
One of the goals of seismic prospecting has been to
determine petrophysical properties of the reservoir (such
as lithology
, porosity and pore fluid type) using remote
measurements, yet little has been done to analyze the ambiguity
and sensitivity of the seismic measurements to the petrophysical
properties of interest. A likely reason for this is that AVO
attributes, commonly used to reduce the risk in qualitatively
determining
petrophysical properties, cannot be easily related to
physical properties of rocks given that the attributes’ amplitudes
give information about changes across
interfaces with no significant information
about the intervals above and below these
interfaces. Furthermore, common practice
has been to estimate two term AVO which
results in two attributes related to changes
of three physical properties of rocks
(P- and S-wave velocity and density) across
interfaces. Unambiguous estimation of the
three properties (Vp, Vs and r) or their
reflectivities is not possible with only two
attributes.
P- and S-wave velocities and density
determine reflection amplitude as a
function of offset, and their estimation (or attributes related to
them) from
seismic data is important given that reservoir
properties in clastic reservoirs are related to these rock properties
through effective media relations.The reconstruction of P- and
S-wave velocity and density logs for different reservoir conditions
through the effective media relationships allows for the
ambiguity and sensitivity analysis of rock properties to different
reservoir conditions. The same rock properties used to analyze
sensitivity and ambiguity through well log reconstruction can be
obtained
from
seismic data by post-stack inversion of AVO
attributes. The resultant seismic data is a measure of rock properties
of subsurface formations (not changes across interfaces)
and can be related directly to well log data.
In this presentation examples of ambiguity and sensitivity analyses of rock properties are presented at both well log and seismic resolution and for the case of two and three term AVO analyses followed by post-stack inversion.
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