Summary
Elastic seismic inversion is a tool frequently used in analysis of seismic
data. Elastic inversion relies on a simplified seismic model and generally
produces 3D cubes for compressional-wave velocity, shear-wave velocity, and
density. By applying rock-physics theory, such volumes may be interpreted in
terms of lithology and fluid properties. Understanding the robustness of
forward and inverse techniques is important when deciding the amount of
information carried by seismic data.
This paper suggests a simple method to update a reservoir characterization
by comparing 4D-seismic data with flow simulations on an existing
characterization conditioned on the base-survey data. The ability to use
results from a 4D-seismic survey in reservoir characterization depends on
several aspects. To investigate this, a loop that performs independent forward
seismic modeling and elastic inversion at two time stages has been
established.
In the workflow, a synthetic reservoir is generated from which data are
extracted. The task is to reconstruct the reservoir on the basis of these data.
By working on a realistic synthetic reservoir, full knowledge of the reservoir
characteristics is achieved. This makes the evaluation of the questions
regarding the fundamental dependency between the seismic and petrophysical
domains stronger. The synthetic reservoir is an ideal case, where properties
are known to an accuracy never achieved in an applied situation. It can
therefore be used to investigate the theoretical limitations of the information
content in the seismic data.
The deviations in water and oil production between the reference and
predicted reservoir were significantly decreased by use of 4D-seismic data in
addition to the 3D inverted elastic parameters.
Introduction
It is well known that the information in seismic data is limited by the
bandwidth of the seismic signal. 4D seismics give information on the changes
between base and monitor surveys and are consequently an important source of
information regarding the principal flow in a reservoir. Because of its limited
resolution, the presence of a thin thief zone can be observed only as a
consequence of flow, and the exact location will not be found directly. This
paper addresses the question of how much information there is in the seismic
data, and how this information can be used to update the model for
petrophysical reservoir parameters.
Several methods for incorporating 4D-seismic data in the
reservoir-characterization workflow for improving history matching have been
proposed earlier. The 4D-seismic data and the corresponding production data are
not on the same scale, but they need to be combined. Huang et al. (1997)
proposed a simulated annealing method for conditioning these data, while Lumley
and Behrens (1997) describe a workflow loop in which the 4D-seismic data are
compared with those computed from the reservoir model. Gosselin et al. (2003)
give a short overview of the use of 4D-seismic data in reservoir
characterization and propose using gradient-based methods for history matching
the reservoir model on seismic and production data. Vasco et al. (2004) show
that 4D data contain information of large-scale reservoir-permeability
variations, and they illustrate this in a Gulf of Mexico example.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
6 June 2005
- Revised manuscript received:
30 June 2006
- Manuscript approved:
31 July 2006
- Version of record:
20 October 2006
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