Borehole Acoustics and Logging
and
Reservoir Delineation
Consortia
Annual Report
1998
Earth Resources Laboratory
Department of Earth, Atmospheric, and Planetary Sciences
Massachusetts Institute of Technology
Cambridge, MA 02139
We would like to express our sincere appreciation to Sue Thrbak and Lori Weldon,
without whose work the publication of this annual report would not be possible.
Copyright
©
1998 Massachusetts Institute of Technology
Earth Resources Laboratory
Copying is permitted only for internal purposes of the sponsors of the
M.LT. Borehole Acoustics and Logging and Reservoir Delineation Consortia
This report was typeset at ERL in Computer Modern Roman using 'I'gX.
Borehole Acoustics and Logging
and Reservoir Delineation
Consortia
Annual Report
1998
Principal Investigator
M. N. Toksiiz
Contributors
A. Al-Dajani
T. Alkhalifah
H. J. Alshammery
C. 1. Burch
D. R. Burns
M. G. Imhof
M. L. Krasovec
O. V. Mikhailov
F. D. Morgan
J. F. Olson
J. H. Queen
P. M. Reppert
W. L. Rodi
F. Shen
J. Sierra
M. N. Toksiiz
Z. Zhu
Report Editors
D. R. Burns
E. A. Henderson
K. Jesdale
Table of Contents
1. EXECUTIVE SUMMARY-CHARACTERIZATION OF
RESERVOIR FLUID FLOW PROPERTIES
by Daniel R. Burns and M. Nafi Toksoz
Introduction. . . . . . . . . . . . . . .
Fluid Flow Induced by Seismic Waves
Fluid Flow Directionality .
Scattering and Scale Effects
Work in Progress . . . . . .
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2. NEAR-SURFACE SCATTERING FROM HIGH VELOCITY
CARBONATES IN WEST TEXAS
by Matthias G. Imhof, M. Nafi Toksoz, Charles I. Burch, and John
H. Queen
Abstract . . . . . . .
2-1
Introduction. . . . .
2-1
2-3
West Texas Dataset
Irregular Topography.
2-6
Near-Subsurface Heterogeneities
2-7
Discussion and Conclusions
2-8
Acknowledgments. . . . . . . . .
2-9
References. . . . . . . . . . . . .
2-10
Appendix A: Boundary Element Method.
2-12
Appendix B: Elastic Multipole Expansions.
2-13
Appendix C: Asymptotic Elastic Free Surface
2-15
Figures
2-21
3. SCALE AND FREQUENCY DEPENDENCE OF REFLECTION
AND TRANSMISSION COEFFICIENTS
by Matthias G. Imhof
Abstract. . .
Introduction .
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3-1
M~~d..
3~
Example. .
Conclusions
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v
Acknowledgments.
References .
Figures
3-6
3-7
3-8
4. SENSITIVITY ANALYSIS OF AMPLITUDE VARIATION WITH
OFFSET (AVO) IN FRACTURED MEDIA
by Mary L. Krasovec, William L. Rodi, and M. Nafi Toksiiz
Abstract . . . . . . .
Introduction. . . . . . .
The Forward Model ..
Results and Discussion.
Conclusions . . . .
Acknowledgments.
References .
Figures
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5. SCATTERING CHARACTERISTICS IN HETEROGENEOUS
FRACTURED RESERVOIRS FROM WAVEFORM ESTIMATION
by Feng Shen and M. Nafi Toksiiz
Abstract . . . . . . . . . . . . . . . . .
Introduction. . . . . . . . . . . . . . .
Signal Parameter Estimator Function
Conclusions . . . .
Acknowledgments. . . . . . . . . . . .
References. . . . . . . . . . . . . . . .
Appendix: Signal Parameter Estimation
Figures
5-1
5-2
5-4
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5-14
5-17
6. SHEAR WAVE BIREFRINGENCE IN REVERSE VSP: AN
APPROACH TO 3-D SURFACE P TO S CONVERTED WAVES
by Jesus Sierra and John H. Queen
Abstract
.
Introduction. . . . . . . . . . . . . . . .
Propagator Matrix Method . . . . . . .
Interpretation of the Propagator Matrix
Synthetic Data and Application.
P to S Converted Waves
Conclusions . . . .
Acknowledgments. . ..
References. . . . . . . .
Appendix: Simulated Annealing
Figures
.
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VI
(
7. REFLECTION MOVEOUT INVERSION FOR HORIZONTAL
TRANSVERSE ISOTROPY: ACCURACY AND LIMITATION
by AbdulFattah AI-Dajani and Tariq Alkhalifah
Abstract. . . . . . . . . . . . . . .
Introduction. . . . . . . . . . . . .
Reflection Moveout in HTI Media.
The Inverse Problem. . . . . . . .
Error Analysis
The Inverse Problem in Layered Media.
Discussion and Conclusions
Acknowledgments. . . . . . . . . . .
References. . . . . . . . . . . . . . .
Appendix: Sign of HTI Parameters.
Figures
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8. BOREHOLE ELECTROSEISMIC MEASUREMENTS IN DOLOMITE:
IDENTIFYING FRACTURES AND PERMEABLE ZONES
by Oleg V. Mikhailov and M. Nafi Toksoz
Abstract. . . . . . . . . . .
8-1
Introduction. . . . . . . . .
8-1
The Physical Phenomenon.
8-2
The Theoretical Model.
8-2
Field Experiments
8-3
mcldD~a.
~3
Discussion . . . . .
Conclusions . . . .
Acknowledgments.
References.
Figures
8-6
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8-7
8-8
9. ELECTROSEISMIC LOGGING FOR THE DETECTION AND
CHARACTERIZATION OF PERMEABLE ZONES:
FIELD MEASUREMENTS AND THEORY
by Oleg V. Mikhailov, Daniel R. Burns, and M. Nafi Toksoz
Abstract. . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction. . . . . . . . . . . . . . . . . . . . . . . .
Electrical Field Induced by a Borehole Stoneley Wave
Electroseismic Logging Technique . . . . . . . . . . . .
Field Experiment . . . . . . . . . . . . . . . . . . . . .
Preliminary Analysis of the Stoneley-Wave-Induced Electrical Signals
Theoretical Model for the Stoneley-Wave-Induced Electrical Potential
Comparison of the Field Data and Theory: Amplitude-Versus-Frequency
Dependence of the Stoneley-Wave-Induced Electrical Potential
vii
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9-15
Discussion . . . . .
Conclusions . . . .
Acknowledgments.
References . . . . .
Appendix A. Analysis of the Mysterious Electrical Signal M-M
Appendix B. Relationships Bet\veen the Amplitude ofthe Electrical Potential
Oscillation and the Amplitudes of the Signals Measured Using the
4-Electrode and the 2-Electrode Arrays
Figures
9-15
9-17
9-17
9~ 19
9-21
9-22
9-24
lO.SEISMOELECTRIC LABORATORY MEASUREMENTS IN
A BOREHOLE
by Zhenya Zhu and M. N afi Toksoz
Abstract. . . . . . . . . . . . . . . .
Introduction. . . . . . . . . . . . . . .
Borehole Models and Measurements .
Results in Fractured Borehole Models
Results in Sandwiched Borehole Models
Conclusions . . . .
Acknowledgments.
References.
Figures
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l1.LABORATORY STUDY OF FREQUENCY DEPENDENT
STREAMING POTENTIALS
by Philip M. Reppert and F. Dale Morgan
Abstract. . .
Introduction. . . . . . .
Theory. . . . . . . . . .
Experimental Approach
Discussion and Applications.
Conclusions . . . .
Acknowledgments.
References .
Figures
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11-2
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12.INTERVAL ATTENUATION ESTIMATION
by Hafiz J. Aishammery and M. Nafi Toksoz
Abstract. . . . .
Introduction. '. . . . . .
Definition of Q . . . . .
Spectral Ratio :rvIethod .
Q Estimation Accuracy
12-1
12-1
12-2
12-3
12-4
V III
Water Tank Experiment
Conclusions . . . .
Acknowledgments.
References .
Figures
.
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12-9
12-10
12-11
12-12
13.TOWARD THE SIMULATION OF ATTENUATION:
OSCILLATORY FLOW IN POROUS ROCK
by John F. Olson
Abstract
.
Introduction
.
Simulation Method .
Preliminary Results
Conclusions . . . .
Acknowledgments.
References .
Figures
.
14.DISPERSION ANALYSIS OF CROSS-DIPOLE DATA
by Xiaojun Huang, Daniel R. Burns, and M. Nafi Toksoz
Abstract
.
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flexural Dispersion and Formation Anisotropy . . . . . . . . . .
A New Rotation Method for Mismatched Sources and Receivers.
Application to Four-Component Cross-Dipole Data.
Effects of Rotation on Dispersion Analysis .
Conclusions . . . .
Acknowledgments.
. . -.'
References .
Figures
.
IX
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14--':10
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EXECUTIVE SUMMARY-CHARACTERIZATION OF
RESERVOIR FLUID FLOW PROPERTIES
Daniel R. Burns and M. Nafi Toksoz
Earth Resources Laboratory
Department of Earth, Atmospheric, and Planetary Sciences
Massachusetts Institute of Technology
Cambridge, MA 02139
INTRODUCTION
The characterization of subsurface fluid flow is the key to exploration, production, and
management of oil, gas, geothermal, and groundwater reservoirs. From a research perspective the question then becomes how can we measure or estimate the spatial variations in physical properties which control the flow of these fluids? Ideally we would
like to be able to remotely identify fluid type and provide accurate estimates of in-situ
porosity and permeability values in three dimensions. In some situations this may be
possible, but in others such a goal may not be attainable. If accurate estimates of these
physical properties cannot be achieved, there may still be important and useful related
information available. For example, being able to provide accurate estimates of the
direction of maximum fluid flow may be a very important piece of information for field
development and drilling decisions. The Earth Resources Laboratory has focused on
developing methods for using seismic waves to estimate flnid flow properties. Seismic
waves provide higher resolution data than potential field measurements, can be polarized for anisotropy measurements, can be used in surface and borehole applications.
and ERL has significant experience in the physics and modeling of wave propagation ill
complex media.
Our report this year provides results in three specific areas related t.o our overall
goal of fluid flow characterization. The first. involves research into methods which utilize
t.he actual motion, induced by seismic waves, of fluids ill porous rock. The passing of a
seismic wave t.hrough a rock cont.aining a viscous fluid result.s in relative motion between
t.he fluid and the solid matrix. This mot.ion dissipates seismic energy resulting in the
att.enuat.ion of the passing wave. The motion of the fluid, which contains ions, also
creates an elect.rical field which can be measured. We present result.s in both of these
areas in this report. A second research area is the measurement of flow direct.ionality.
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Burns
The presence of open fractures with a preferred orientation will control the direction
of fluid flow in a reservoir. Such fractures will also have a large effect on the elastic
properties of the reservoir rock. The resulting elastic anisotropy may be observable in
both surface seismic data as well as borehole acoustic logs. We present several papers on
the effects of anisotropy on surface seismic data and AVO signatures, as well as on dipole
sonic logs. Finally, because fluid flow is only one of the many factors which effect seismic
waves, we must continue to improve our understanding of wave propagation in complex
media. We present two such papers which look at scattering and scale dependent issues.
The way in which property variations at different spatial scales affect seismic waves is
an important research area that we will continue to investigate in the coming year.
The following sections provide a more detailed summary of the results in each of
these three broad areas.
FLUID FLOW INDUCED BY SEISMIC WAVES
A seismic wave impinging on a fluid-filled porous rock results in relative motion between
the viscous fluid and the solid matrix. This motion may be bulk flow or local '~quirt'
flow. Although there is evidence of both types of mechanisms from laboratory studies
of rock samples, the way that fluid moves in a porous rock when a seismic wave passes
is not well understood. Regardless of the mechanism, such relative motion results in
attenuation of the seismic wave, with the frequency dependence of that attenuation
being related to the type of fluid flow mechanism at work. Olson presents a numerical
modeling approach that allows us to visualize such fluid motion. His results provide an
exciting glimpse into the complexity of fluid flow in rocks, and will help us to understand
the dominant attenuation mechanisms in different rocks.
The use of surface seismic data to estimate fluid flow properties based on attenuation measurements is much more difficult. In order to use reflection data to estimate
variations in reservoir attenuation, we must be able to isolate any amplitude changes
to a specific interval of interest. Alshammery and Toksoz present results from a laboratory study in which they estimate the quality factor of several materials based on
a comparison of the reflections from the top and base of a slab suspended in a water
tank. The Q estimates they obtain are in good agreement with the actual values, but
they point out that overburden attenuation may degrade the estimates as a function of
source receiver offset due to different travel path lengths.
When a seismic wave induces fluid flow, a streaming electrical current is produced.
This current is caused by the adsorption of charged ions to the surface of the solid grains,
and the resulting charge excess in the pore fluid. The relative motion of this fluid creates
an electrical field which can be measured. This electroseismic effect provides another
way to measure remotely the movement of fluids in a reservoir. Mikhailov et al. present
field observations of this phenomenon in a borehole logging mode. They show that the
effect can be measured in the field in sedimentary rocks (dolomite), and that the effect
can be related to the interconnected porosity in the formation. They also find that by
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Executive Summary
making the measurement over a range of frequencies, it may be possible to estimate
the permeability of the formation. Zhu and Toksoz likewise study the electroseismic
logging technique in laboratory scale models. Their results indicate that this effect can
be used to identify open fractures, and that the amplitude of the signal is related to the
fracture aperture. Finally, Reppert and Morgan provide laboratory measurements of the
streaming potential caused by fluid motion through porous materials. They measured
the effect for a capillary tube, a porous filter, and a sample of Boise Sandstone over a
frequency range which covered the critical frequency for each material. Their estimates
for the average pore diameter based on the critical frequency are in good agreement
with the actual values, and support the idea that the measurement of electroseismic
data over a range of frequencies may provide a means of estimating permeability.
FLUID FLOW DIRECTIONALITY
Although we are most interested in obtaining direct indicators of in-situ permeability
variations, information about the direction of fluid flow can be critically important for
reservoir development decisions. The presence of aligned fractures results in elastic
anisotropy which can be characterized by seismic measurements. AVO measurements
as a function of azimuth can provide information about the orientation of fractures and
the fracture density which is related to the fluid volume and permeability. Krasovec
et al. studied the sensitivity of AVO parameters to fracture density, pore fluid, and
lithology variations. They found that the 'c' parameter in a three-term Shuey-type
parameterization of the AVO behavior is particularly sensitive to fracture density variations for vertical fractures. Shen et al., using 3-D finite difference models and field data,
found that the spectral characteristics of reflections from the top and base of a fractured
reservoir contain information about fracture density and the correlation scale lengths
of the fracture distribution. They used a high resolution spectral analysis technique to
study variations in the spectral signatures of reflections as a function of offset. Their
results indicate that scattering from fractures aligned normal to the propagation path
results in more energy at higher frequencies as a function of offset than would be seen
for data acquired in areas without fractures or along the fracture strike.
Al-Dajani and Alkhalifah investigate the effect of an HTI medium on the normal
moveout of seismic reflections as a function of azimuth. If measurements are available
for several source-receiver azimuths, the anisotropy parameter and symmetry axis direction can be obtained. Sierra and Queen present a method for estimating shear wave
birefringence from 3-D surface P-S converted wave data based on an equivalent reverseVSP formulation. They show that it is possible, using a range of frequencies and offsets,
to obtain information about 'subsurface anisotropy from converted wave data.
In-situ anisotropy directions, due to aligned fractures, stress, or intrinsic material
properties, can also be obtained from cross-dipole sonic logs. Huang et al. present
a frequency domain rotation method that handles situations in which the two dipole
sources are not matched. This method can improve the accuracy of the rotation of
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the data into fast and slow shear wave directions. Accurate rotation is also critical for
analyzing differences in the dispersion characteristics of the fast and slow flexural modes.
Differences between these dispersion curves may indicate variations in the propagation
directions as a function of distance from the borehole.
SCATTERING AND SCALE EFFECTS
The characterization of fluid flow effects in reservoirs takes place within the context of
complex subsurface geological conditions which scatter seismic energy. These scattering
effects can provide us with information about the nature of small-scale heterogeneities
which may impact reservoir production. However, if we are interested in the analysis of
subtle fluid flow effects in seismic data, such scattering may be an unwelcome complication. Imhof et al. studied the effects of near-surface scattering on seismic reflection
data. They found that for data acquired in West Texas, scattering was dominated by
the presence of vugs and cavities in the near surface limestones. These heterogeneities
set up a waveguide that trapped energy near the surface. Irregular topography and
heterogeneous weathering layers did not appear to be important factors for this data.
Imhof, in a second paper, studied the effect of different spatial scale heterogeneities
on the reflection and transmission of seismic waves. Using wavelet transforms to filter
different spatial scales from a sonic log, he calculated reflection and transmission coefficients as a function of frequency. The results indicate that transmission coefficients
are generally independent of frequency and scale, while reflection coefficients are very
sensitive to even the small-scale perturbations of slowness.
WORK IN PROGRESS
A number of other related projects are ongoing at ERL, including: geostatistics, fast
wave propagation modeling and imaging algorithms (phase-screen type propagators;
variable grid finite difference methods), hydrofracture imaging and monitoring, VSP
while drilling, and a field acquisition research program that includes reverse VSP using
a downhole vibrator source and surface 3-D seismic using random receiver layouts.
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