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Difference between revisions of "Acoustic logging"

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Petroleum applications of acoustic-wave-propagation theory and physics include both:
 
Petroleum applications of acoustic-wave-propagation theory and physics include both:
 +
 
*Surface-geophysical methods
 
*Surface-geophysical methods
 
*Borehole-geophysical methods
 
*Borehole-geophysical methods
Acoustic logging is a subset of borehole-geophysical acoustic techniques.  
+
 
 +
Acoustic logging is a subset of borehole-geophysical acoustic techniques.
  
 
Historically, the primary and the most routine uses of acoustic logs in reservoir engineering have been:
 
Historically, the primary and the most routine uses of acoustic logs in reservoir engineering have been:
*[[Porosity evaluation with acoustic logging|Porosity determination]]
 
*[[Fluid identification and characterization|Identification of gas-bearing intervals]]
 
*[[Cement bond logs|Cement evaluation]]
 
Continuing developments in tool hardware and in interpretation techniques have expanded the utility of these logs in formation evaluation and completion (fracture) design and evaluation.
 
  
==Overview==
+
*[[Porosity_evaluation_with_acoustic_logging|Porosity determination]]
A virtual explosion in the volume of acoustic research conducted over the past 20 years has resulted in significant advances in the fundamental understanding of downhole acoustic measurements. These advances, in turn, have greatly influenced practical logging technology by allowing [[Acoustic logging tools|logging-tool designs]] to be optimized for specific applications.<ref name="r1" />
+
*[[Fluid_identification_and_characterization|Identification of gas-bearing intervals]]
 +
*[[Cement_bond_logs|Cement evaluation]]
 +
 
 +
Continuing developments in tool hardware and in interpretation techniques have expanded the utility of these logs in formation evaluation and completion (fracture) design and evaluation.
 +
 
 +
== Overview ==
  
Acoustic-wave data-acquisition methods cover a broad range of scales from millimeters to hundreds of meters ('''Fig. 1'''). '''Table 1''' lists other common surface- and borehole-geophysical methods.
+
A virtual explosion in the volume of acoustic research conducted over the past 20 years has resulted in significant advances in the fundamental understanding of downhole acoustic measurements. These advances, in turn, have greatly influenced practical logging technology by allowing [[Acoustic_logging_tools|logging-tool designs]] to be optimized for specific applications.<ref name="r1">Cheng, C.H., Paillet, F.L., and Pennington, W.D. 1992. Acoustic-Waveform Logging--Advances In Theory and Application. The Log Analyst 33 (3): 239. SPWLA-1992-v33n3a2.</ref>
 +
 
 +
Acoustic-wave data-acquisition methods cover a broad range of scales from millimeters to hundreds of meters ('''Fig. 1<ref name="r2">Coates, R., Kane, M., Chang, C. et al. 2000. Single-well Sonic Imaging: High-Definition Reservoir Cross-sections from Horizontal Wells. Presented at the SPE/CIM International Conference on Horizontal Well Technology, Calgary, Alberta, Canada, 6-8 November 2000. SPE-65457-MS. http://dx.doi.org/10.2118/65457-MS</ref>'''). '''Table 1''' lists other common surface- and borehole-geophysical methods.
  
 
<gallery widths="300px" heights="200px">
 
<gallery widths="300px" heights="200px">
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Borehole acoustic-logging measurements are used in a wide variety of geophysical, geological, and engineering applications and play an important role in the following undertakings ('''Table 2'''):
 
Borehole acoustic-logging measurements are used in a wide variety of geophysical, geological, and engineering applications and play an important role in the following undertakings ('''Table 2'''):
 +
 
*Evaluating reservoirs
 
*Evaluating reservoirs
 
*Reducing exploration and production risks
 
*Reducing exploration and production risks
 
*Selecting well locations
 
*Selecting well locations
 
*Designing completions
 
*Designing completions
*Increasing hydrocarbon recovery  
+
*Increasing hydrocarbon recovery
  
<gallery widths=300px heights=200px>
+
<gallery widths="300px" heights="200px">
 
File:Vol5 Page 0169 Image 0002.png|'''Table 2'''
 
File:Vol5 Page 0169 Image 0002.png|'''Table 2'''
 
</gallery>
 
</gallery>
  
[[Acoustic logging tools|Modern logging tools]] include conventional borehole-compensated (BHC) monopole devices as well as the newer array devices—both monopole and multipole (monopole/dipole)—and [[Acoustic logging while drilling|logging-while-drilling]] (LWD) acoustic services. These logging tools provide acoustic measurements in all borehole mud types (but not in air- or foam-filled boreholes) in vertical, deviated, and horizontal wells, in both open and cased hole. They are combinable with other logging devices and are available in a variety of sizes to accommodate a range of borehole and casing diameters. Specialized tool designs are used for [[Cement bond logs|cement and casing evaluation]] and borehole imaging.  
+
[[Acoustic_logging_tools|Modern logging tools]] include conventional borehole-compensated (BHC) monopole devices as well as the newer array devices—both monopole and multipole (monopole/dipole)—and [[Acoustic_logging_while_drilling|logging-while-drilling]] (LWD) acoustic services. These logging tools provide acoustic measurements in all borehole mud types (but not in air- or foam-filled boreholes) in vertical, deviated, and horizontal wells, in both open and cased hole. They are combinable with other logging devices and are available in a variety of sizes to accommodate a range of borehole and casing diameters. Specialized tool designs are used for [[Cement_bond_logs|cement and casing evaluation]] and borehole imaging.
 +
 
 +
== Geophysical applications ==
 +
 
 +
The higher operating frequency of acoustic-logging tools and the smaller TR distances allows for higher-quality velocity data and finer vertical resolution than surface reflection techniques. Acoustic-velocity logs were originally developed for calibrating surface seismic velocities and reflectors. Acoustic-log interval travel time or transit time, Δ''t'', can be summed, i.e., integrated, over the entire logged interval to provide the equivalent of seismic one-way time which is compared to borehole seismic surveys and reflection seismic two-way time.
  
==Geophysical applications==
+
Acoustic-log data are commonly calibrated using checkshot (velocity) or [[Seismic_profiling|vertical seismic profile]] (VSP) surveys prior to use in geophysical applications. Data from these surveys, which use downhole receivers and surface acoustic sources, are used to adjust the log data for drift and borehole conditions and result in improved time-depth correlation. Acoustic-log data are combined with density-log data, to generate an impedance log that in turn is used to produce a synthetic seismogram. Synthetic seismograms are artificial seismic records that tie seismic time to log depth and are also used to match well-log quantities to seismic attributes for distinguishing primary seismic events (geologic structure and stratigraphy). It is possible, however, that a synthetic seismogram may not provide a very good match to the seismic field data. Disagreements commonly result from the differences scale and acquisition physics used in seismic and well-log measurement; for example<ref name="r3">Thomas, D.H. 1978. Seismic Applications of Sonic Logs. The Log Analyst 19 (1): 23–32.</ref><ref name="r4">Liner, C.L. Interpreting Seismic Data. 2000. Exploring for Oil and Gas Traps, Treatise of Petroleum Geology, Handbook of Petroleum Geology E.A. Beaumont, and N.H. Foster eds., Chap. 12, 12-13–12–17. Tulsa, Oklahoma: AAPG.</ref><ref name="r5">Bork, J. and Wood, L.C. 2001. Seismic Interpretation of Sonic Logs, paper INT 1.4. Expanded Abstracts, 2001 Annual Meeting Technical Program, SEG, 510–513.</ref><ref name="r6">Box, R., and Lowrey, P. 2003. Reconciling Sonic Logs with Check-Shot Surveys; Stretching Synthetic Seismograms. The Leading Edge 22 (6): 510–517. http://dx.doi.org/10.1190/1.1587672</ref><ref name="r7">White, R.E. 2003. Tying Well-Log Synthetic Seismograms to Seismic Data: The Key Factors, paper W-3.7. Expanded Abstracts, 2003 Annual Meeting Technical Program, SEG, 2449–2452.</ref>:
The higher operating frequency of acoustic-logging tools and the smaller TR distances allows for higher-quality velocity data and finer vertical resolution than surface reflection techniques. Acoustic-velocity logs were originally developed for calibrating surface seismic velocities and reflectors. Acoustic-log interval travel time or transit time, Δ''t'', can be summed, i.e., integrated, over the entire logged interval to provide the equivalent of seismic one-way time which is compared to borehole seismic surveys and reflection seismic two-way time.  
 
  
Acoustic-log data are commonly calibrated using checkshot (velocity) or [[Seismic profiling|vertical seismic profile]] (VSP) surveys prior to use in geophysical applications. Data from these surveys, which use downhole receivers and surface acoustic sources, are used to adjust the log data for drift and borehole conditions and result in improved time-depth correlation. Acoustic-log data are combined with density-log data, to generate an impedance log that in turn is used to produce a synthetic seismogram. Synthetic seismograms are artificial seismic records that tie seismic time to log depth and are also used to match well-log quantities to seismic attributes for distinguishing primary seismic events (geologic structure and stratigraphy). It is possible, however, that a synthetic seismogram may not provide a very good match to the seismic field data. Disagreements commonly result from the differences scale and acquisition physics used in seismic and well-log measurement; for example<ref name="r3" /><ref name="r4" /><ref name="r5" /><ref name="r6" /><ref name="r7" />:
 
 
*Operational frequency (wavelength)
 
*Operational frequency (wavelength)
 
*Borehole condition
 
*Borehole condition
 
*Angle of measurement (particularly in the presence of anisotropy)
 
*Angle of measurement (particularly in the presence of anisotropy)
  
Acoustic-log data provide a fundamental and essential element of modern seismic reservoir characterization.<ref name="r8" /> See [[Geophysics|fundamentals of geophysics]] for more information on the determination and use of these types of analyses.
+
Acoustic-log data provide a fundamental and essential element of modern seismic reservoir characterization.<ref name="r8">Walls, J., Dvorkin, J., and Carr, M. 2004. Well Logs and Rock Physics in Seismic Reservoir Characterization. Presented at the Offshore Technology Conference, Houston, Texas, 3-6 May. OTC-16921-MS. http://dx.doi.org/10.4043/16921-MS</ref> See [[Geophysics|fundamentals of geophysics]] for more information on the determination and use of these types of analyses.
 +
 
 +
== Near-well imaging ==
 +
 
 +
Acoustic data acquired using modern array tools can provide high-resolution (0.5 m), microscale "seismic" 2D and 3D images of structural features in the near-borehole region (10 to 15 m). Conventional seismic-processing techniques, including filtering and migration, are used to extract compressional and shear reflections from the acoustic data. The reflections are then used to image geological features near the borehole. This technique allows the imaging of ('''Fig. 2''')<ref name="r9">Pistre, V. et al. 2005. A Modular Wireline Sonic Tool for Measurements of 3D (Azimuthal, Radial, and Axial) Formation Acoustic Properties, paper P. Trans., 2005 Annual Logging Symposium, SPWLA, 1–13.</ref><ref name="r10">Hornby, B. 1989. Imaging of near‐borehole structure using full‐waveform sonic data. Geophysics 54 (6): 747–757. http://dx.doi.org/10.1190/1.1442702</ref><ref name="r11">Hornby, B.E. 1995. Use of Full-Wave Sonic Data to Image Near-Borehole Structural Features. Petroleum Geoscience 1 (2): 109–114.</ref><ref name="r12">Esmeroy, C. et al. 1997. Sonic Imaging—A Tool for High-Resolution Reservoir Description, paper BH 2.7. Expanded Abstracts, 1997 Annual Meeting Technical Program, SEG, 1, 278–281.</ref><ref name="r13">Tang, X.-M. and Cheng, A. 2004. Quantitative Borehole Acoustic Methods. In Handbook of Geophysical Exploration, Seismic Exploration, Vol. 24. Oxford, England: Pergamon Press (Elsevier).</ref><ref name="r14">Chabot, L. et al. 2001. Single-Well Imaging Using the Full Waveform of an Acoustic Sonic, paper BH 3.7. Expanded Abstracts, 2001 Annual Meeting Technical Program, SEG, 420–423.</ref><ref name="r15">Yamamoto, H., Watanabe, S., Koelman, J.M.V. et al. 2000. Borehole Acoustic Reflection Survey Experiments in Horizontal Wells for Accurate Well Positioning. Presented at the SPE/CIM International Conference on Horizontal Well Technology, Calgary, Alberta, Canada, 6-8 November 2000. SPE-65538-MS. http://dx.doi.org/10.2118/65538-MS</ref><ref name="r16">Tang, X.M. 2004. Imaging Near-Borehole Structure Using Directional Acoustic-Wave Measurement. Geophysics 69 (6): 1378–1386. http://dx.doi.org/10.1190/1.1836812</ref><ref name="r17">Zheng, Y., and Tang, X. 2005. Imaging Near-Borehole Structure Using Acoustic Logging Data with Prestack F-K Migration, paper BG 2. Expanded Abstracts, 2005 Annual Meeting Technical Program, SEG, 360–363.</ref>:
  
==Near-well imaging==
 
Acoustic data acquired using modern array tools can provide high-resolution (0.5 m), microscale "seismic" 2D and 3D images of structural features in the near-borehole region (10 to 15 m). Conventional seismic-processing techniques, including filtering and migration, are used to extract compressional and shear reflections from the acoustic data. The reflections are then used to image geological features near the borehole. This technique allows the imaging of ('''Fig. 2''')<ref name="r9" /><ref name="r10" /><ref name="r11" /><ref name="r12" /><ref name="r13" /><ref name="r14" /><ref name="r15" /><ref name="r16" /><ref name="r17" />:
 
 
*Bed boundaries
 
*Bed boundaries
 
*Thin beds (stringers)
 
*Thin beds (stringers)
Line 55: Line 65:
 
</gallery>
 
</gallery>
  
==Acoustic theory and wave propagation==
+
== Acoustic theory and wave propagation ==
The principles of borehole acoustic logging (and surface seismic methods) are based on the theory of [[Seismic wave propagation|wave propagation]] in an elastic medium, as detailed in several sources<ref name="r18" /><ref name="r19" /><ref name="r20" /><ref name="r13" />. The oscillating motion generated by a sound source (transducer) in an elastic medium (rock formation) is called an elastic wave or acoustic wave (also called head or body waves). Wave theory predicts how an acoustic signal propagates through the borehole and formation. Snell’s law explains how the acoustic signal behaves at the velocity boundary separating the borehole and the formation, that is, how it is transmitted into the formation and back to the receivers. Elasticity is the property of matter that causes it to resist deformation in volume or shape. It is the elastic nature of rock formations that permits wave propagation. Acoustic waves have four measurable properties:  
+
 
*[[Acoustic velocity dispersion and attenuation|Velocity]]
+
The principles of borehole acoustic logging (and surface seismic methods) are based on the theory of [[Seismic_wave_propagation|wave propagation]] in an elastic medium, as detailed in several sources<ref name="r18">Paillet, F.L. and Cheng, C.H. 1991. Acoustic Waves in Boreholes, 1–264. Boca Raton, Florida: CRC Press.</ref><ref name="r19">Mavko, G., Mukerji, T., and Dvorkin, J. 1998. The Rock Physics Handbook—Tools for Seismic Analysis in Porous Media, 1-329. Cambridge, England: Cambridge University Press.</ref><ref name="r20">Hearst, J.R., Nelson, P.H., and Paillet, F.L. 2000. Acoustic Logging, Well Logging for Physical Properties, second edition, Chap. 8, 257–303. New York City: Wiley and Sons Inc.</ref><ref name="r13">Tang, X.-M. and Cheng, A. 2004. Quantitative Borehole Acoustic Methods. In Handbook of Geophysical Exploration, Seismic Exploration, Vol. 24. Oxford, England: Pergamon Press (Elsevier).</ref>. The oscillating motion generated by a sound source (transducer) in an elastic medium (rock formation) is called an elastic wave or acoustic wave (also called head or body waves). Wave theory predicts how an acoustic signal propagates through the borehole and formation. Snell’s law explains how the acoustic signal behaves at the velocity boundary separating the borehole and the formation, that is, how it is transmitted into the formation and back to the receivers. Elasticity is the property of matter that causes it to resist deformation in volume or shape. It is the elastic nature of rock formations that permits wave propagation. Acoustic waves have four measurable properties:
 +
 
 +
*[[Acoustic_velocity_dispersion_and_attenuation|Velocity]]
 
*Amplitude
 
*Amplitude
 
*Amplitude attenuation
 
*Amplitude attenuation
 
*Frequency
 
*Frequency
  
[[Acoustic logging tools]] are designed to measure one or more of these properties, with velocity (slowness) being the most common.  
+
[[Acoustic_logging_tools|Acoustic logging tools]] are designed to measure one or more of these properties, with velocity (slowness) being the most common.
  
 
The waveform recorded at the logging tool’s receivers is a composite signal containing different energy modes, each with a different frequency, velocity, and amplitude. For borehole logging, the modes of primary interest ('''Fig. 3''') are, in order of arrival:
 
The waveform recorded at the logging tool’s receivers is a composite signal containing different energy modes, each with a different frequency, velocity, and amplitude. For borehole logging, the modes of primary interest ('''Fig. 3''') are, in order of arrival:
 +
 
*Compressional
 
*Compressional
 
*Shear
 
*Shear
*Stoneley (tube) waves  
+
*Stoneley (tube) waves
  
 
The waveform is recorded as acoustic amplitude as a function of time.
 
The waveform is recorded as acoustic amplitude as a function of time.
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These waves are transmitted through the medium some distance from the origin of displacement. The particles of the medium do not travel with the wave, but only vibrate around their mean central position. Acoustic waves are classified according to the direction of particle displacement with respect to the direction of wave propagation as either:
 
These waves are transmitted through the medium some distance from the origin of displacement. The particles of the medium do not travel with the wave, but only vibrate around their mean central position. Acoustic waves are classified according to the direction of particle displacement with respect to the direction of wave propagation as either:
 +
 
*Longitudinal (i.e., particle displacement is parallel to the direction of propagation)
 
*Longitudinal (i.e., particle displacement is parallel to the direction of propagation)
 
*Transverse (i.e., direction of particle displacement is perpendicular to the direction of propagation)
 
*Transverse (i.e., direction of particle displacement is perpendicular to the direction of propagation)
  
In acoustic logging:  
+
In acoustic logging:
 +
 
 
*The longitudinal wave is known as the compressional wave
 
*The longitudinal wave is known as the compressional wave
 
*The transverse wave is known as the shear wave
 
*The transverse wave is known as the shear wave
  
The presence of the borehole excites two additional acoustic energy modes, called guided waves:  
+
The presence of the borehole excites two additional acoustic energy modes, called guided waves:
*Normal (pseudo-Rayleigh)
 
*Tube (Stoneley) waves
 
  
Acoustic-wave velocity is controlled by a number of factors:  
+
*Normal (pseudo-Rayleigh)
*[[Rock types|Lithology (mineralogy)]]
+
*Tube (Stoneley) waves
 +
 
 +
Acoustic-wave velocity is controlled by a number of factors:
 +
 
 +
*[[Rock_types|Lithology (mineralogy)]]
 
*Cementation
 
*Cementation
 
*Clay content
 
*Clay content
 
*Texture
 
*Texture
*[[Rock acoustic velocities and porosity|Porosity]]
+
*[[Rock_acoustic_velocities_and_porosity|Porosity]]
 
*Pore-fluid composition and saturation
 
*Pore-fluid composition and saturation
*[[Rock acoustic velocities and in-situ stress|Overburden-and pore-fluid pressure (stress)]]
+
*[[Rock_acoustic_velocities_and_in-situ_stress|Overburden-and pore-fluid pressure (stress)]]
*[[Rock acoustic velocities and temperature|Temperature]]
+
*[[Rock_acoustic_velocities_and_temperature|Temperature]]
 +
 
 +
The rock’s mechanical properties, elastic dynamics, and [[Rock_density_and_porosity|density]] are a constant for a particular homogeneous and isotropic material. Acoustic-wave velocity can be related to rock elastic properties through three constants of:
  
The rock’s mechanical properties, elastic dynamics, and [[Rock density and porosity|density]] are a constant for a particular homogeneous and isotropic material. Acoustic-wave velocity can be related to rock elastic properties through three constants of:
 
 
*Proportionality
 
*Proportionality
 
*Elastic moduli (e.g., Young’s, shear, and bulk)
 
*Elastic moduli (e.g., Young’s, shear, and bulk)
 
*Poisson’s ratio
 
*Poisson’s ratio
  
This serves as the basis for mechanical-property evaluation by acoustic logs. In reality, most petroleum reservoirs contain varying pore sizes, pore fill (e.g., clays), fractures, etc. and consequently, are neither truly isotropic nor homogeneous. Furthermore, in fluid-saturated rocks, these acoustic properties also depend on the type and volume of fluids present.  
+
This serves as the basis for mechanical-property evaluation by acoustic logs. In reality, most petroleum reservoirs contain varying pore sizes, pore fill (e.g., clays), fractures, etc. and consequently, are neither truly isotropic nor homogeneous. Furthermore, in fluid-saturated rocks, these acoustic properties also depend on the type and volume of fluids present.
  
===Compressional waves===
+
=== Compressional waves ===
  
 
Compressional (P, primary, or pressure) waves are longitudinal waves that are transmitted through an elastic formation by compression or pressure. Particle motion is parallel to the direction of wave propagation ('''Fig. 4'''). They can travel through solids, liquids, and gases and are the fastest wave type—they represent the acoustic first arrival. Of all acoustic wave types, they are the most reliable because they are least affected by:
 
Compressional (P, primary, or pressure) waves are longitudinal waves that are transmitted through an elastic formation by compression or pressure. Particle motion is parallel to the direction of wave propagation ('''Fig. 4'''). They can travel through solids, liquids, and gases and are the fastest wave type—they represent the acoustic first arrival. Of all acoustic wave types, they are the most reliable because they are least affected by:
 +
 
*Faults
 
*Faults
 
*Unconsolidated formations
 
*Unconsolidated formations
 
*Borehole fluids
 
*Borehole fluids
  
The wave is transmitted by both the rock matrix (i.e., the framework) and the fluid present in the pore throats. A compression, together with an adjacent rarefaction preceding or following it, constitutes a complete cycle. The distance between complete cycles is called the wave length and the number of cycles propagating through a point in the medium per unit time is the frequency. The velocity of elastic-wave propagation in an isotropic homogeneous medium can be derived from a combination of the theory of elasticity with Newton’s law of motion. Compressional-wave velocity (or travel time) is a function of the density and elasticity of the medium and is a constant for a given material.  
+
The wave is transmitted by both the rock matrix (i.e., the framework) and the fluid present in the pore throats. A compression, together with an adjacent rarefaction preceding or following it, constitutes a complete cycle. The distance between complete cycles is called the wave length and the number of cycles propagating through a point in the medium per unit time is the frequency. The velocity of elastic-wave propagation in an isotropic homogeneous medium can be derived from a combination of the theory of elasticity with Newton’s law of motion. Compressional-wave velocity (or travel time) is a function of the density and elasticity of the medium and is a constant for a given material.
  
 
<gallery widths="300px" heights="200px">
 
<gallery widths="300px" heights="200px">
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=== Shear and borehole flexural waves ===
 
=== Shear and borehole flexural waves ===
Shear (S, secondary) waves are transverse waves that are transmitted by lateral displacement of particles in a rigid elastic formation. Particle motion is perpendicular to the direction of motion ('''Fig. 4'''). Normally, shear waves are the second arrival in an acoustic wave train. In most reservoir rocks, shear waves generally have higher amplitudes than compressional waves but lower velocities, by as much 40 to 50%. There are two types of borehole shear waves—direct and indirect, also known as refracted or induced. Indirect shear waves are induced in a formation through a process known as mode conversion in which some of the compressional energy is transferred from the borehole fluid into the rock formation. Monopole transmitters generate these indirect shear waves while dipole transmitters generate direct shear waves by inducing a flexural (asymmetric mode) in the borehole. Shear-wave propagation requires a medium that has shear strength (rigidity). Consequently, shear waves can only travel in solids, not in liquids or gas. In liquids and gas, the shear head-wave generated within the formation is converted into a compressional wave and propagated back across the borehole fluid to the acoustic receivers as a later-arriving compressional wave.
 
  
Unconsolidated or poorly consolidated sandstones ("soft" or "slow" rocks) are less rigid and more compressible than well-consolidated ("hard" or "fast") rocks. When the formation shear-wave velocity is less than the acoustic velocity of the borehole fluid (''V''<sub>''s''</sub> < ''V''<sub>''f''</sub>), a rock formation is called "slow." There is no refracted shear-wave from monopole devices in slow formations and low-frequency dipole transmission and reception is required to adequately detect low-frequency flexural arrivals for the shear-wave slowness determination. However, if a monopole-array tool is used in these conditions, a shear-wave slowness can be estimated from Stoneley-wave velocity dispersion.<ref name="r21" /> In very slow formations, where ''V''<sub>''c''</sub> < ''V''<sub>''f''</sub>, special processing may be required to extract the formation compressional signal.<ref name="r22" />  
+
Shear (S, secondary) waves are transverse waves that are transmitted by lateral displacement of particles in a rigid elastic formation. Particle motion is perpendicular to the direction of motion ('''Fig. 4'''). Normally, shear waves are the second arrival in an acoustic wave train. In most reservoir rocks, shear waves generally have higher amplitudes than compressional waves but lower velocities, by as much 40 to 50%. There are two types of borehole shear waves—direct and indirect, also known as refracted or induced. Indirect shear waves are induced in a formation through a process known as mode conversion in which some of the compressional energy is transferred from the borehole fluid into the rock formation. Monopole transmitters generate these indirect shear waves while dipole transmitters generate direct shear waves by inducing a flexural (asymmetric mode) in the borehole. Shear-wave propagation requires a medium that has shear strength (rigidity). Consequently, shear waves can only travel in solids, not in liquids or gas. In liquids and gas, the shear head-wave generated within the formation is converted into a compressional wave and propagated back across the borehole fluid to the acoustic receivers as a later-arriving compressional wave.
 +
 
 +
Unconsolidated or poorly consolidated sandstones ("soft" or "slow" rocks) are less rigid and more compressible than well-consolidated ("hard" or "fast") rocks. When the formation shear-wave velocity is less than the acoustic velocity of the borehole fluid (''V''<sub>''s''</sub> < ''V''<sub>''f''</sub>), a rock formation is called "slow." There is no refracted shear-wave from monopole devices in slow formations and low-frequency dipole transmission and reception is required to adequately detect low-frequency flexural arrivals for the shear-wave slowness determination. However, if a monopole-array tool is used in these conditions, a shear-wave slowness can be estimated from Stoneley-wave velocity dispersion.<ref name="r21">Cheng, C.H. and Toksoz, M.N. 1983. Determination of Shear Wave Velocities in ‘Slow’ Formation, paper V, Trans., 1983 Annual Logging Symposium, Soc. of Professional Well Log Analysts (SPWLA) 1–18.</ref> In very slow formations, where ''V''<sub>''c''</sub> < ''V''<sub>''f''</sub>, special processing may be required to extract the formation compressional signal.<ref name="r22">Valero, H.P., Peng, L., Yamamoto, M. et al. 2004. Processing of Monopole Compressional In Slow Formation. Presented at the SEG Annual Meeting, Denver, Colorado, 10-15 October.</ref>
  
 
Flexural-wave velocity varies with frequency—a phenomenon called dispersion. In contrast, the compressional and shear headwaves generated by monopole sources are generally not dispersive. At very low frequencies, the flexural wave travels at the formation shear velocity. This dispersion effect diminishes as the wavelength of the flexural-wave increases and is generally minimal when the wavelength is at least three times the borehole diameter. Fast formations exhibit a center frequency slightly greater than 3 kHz, while slow formations exhibit a center frequency of ≈ 1 kHz, or less. The received frequency spectrum of a dipole array is a function of:
 
Flexural-wave velocity varies with frequency—a phenomenon called dispersion. In contrast, the compressional and shear headwaves generated by monopole sources are generally not dispersive. At very low frequencies, the flexural wave travels at the formation shear velocity. This dispersion effect diminishes as the wavelength of the flexural-wave increases and is generally minimal when the wavelength is at least three times the borehole diameter. Fast formations exhibit a center frequency slightly greater than 3 kHz, while slow formations exhibit a center frequency of ≈ 1 kHz, or less. The received frequency spectrum of a dipole array is a function of:
 +
 
*Transmitter frequency
 
*Transmitter frequency
 
*Rock properties
 
*Rock properties
 
*Borehole size
 
*Borehole size
  
Modern dipole transmitters are broadband transmitters, i.e., they operate over a range of frequencies, to account for dispersion and to accommodate different formation types.  
+
Modern dipole transmitters are broadband transmitters, i.e., they operate over a range of frequencies, to account for dispersion and to accommodate different formation types.
 +
 
 +
=== Stoneley waves ===
 +
 
 +
Stoneley (tube) waves are high-amplitude guided waves that are generated by a radial (symmetric) flexing of the borehole as the acoustic energy passes from the borehole fluid into the rock formation. They propagate at low frequencies along the fluid-rock interface at the borehole wall; hence, they are sensitive to the rock properties adjacent to the borehole wall. They are the slowest acoustic mode. They can be measured in both open and cased boreholes, but in cased holes Stoneley-wave features are primarily controlled by the casing rigidity. Similarly to shear waves, Stoneley waves are also dispersive; i.e., wave velocity varies with frequency—the amount of dispersion is related to formation rock properties. However, Stoneley waves are notable for several special properties:
  
===Stoneley waves===
 
Stoneley (tube) waves are high-amplitude guided waves that are generated by a radial (symmetric) flexing of the borehole as the acoustic energy passes from the borehole fluid into the rock formation. They propagate at low frequencies along the fluid-rock interface at the borehole wall; hence, they are sensitive to the rock properties adjacent to the borehole wall. They are the slowest acoustic mode. They can be measured in both open and cased boreholes, but in cased holes Stoneley-wave features are primarily controlled by the casing rigidity. Similarly to shear waves, Stoneley waves are also dispersive; i.e., wave velocity varies with frequency—the amount of dispersion is related to formation rock properties. However, Stoneley waves are notable for several special properties:
 
 
*There is no cut-off frequency
 
*There is no cut-off frequency
 
*Dispersion is very mild
 
*Dispersion is very mild
 
*For all frequencies, Stoneley-wave velocity is less than fluid velocity
 
*For all frequencies, Stoneley-wave velocity is less than fluid velocity
*Group velocity nearly equals phase velocity over the frequency range  
+
*Group velocity nearly equals phase velocity over the frequency range
 +
 
 +
All acoustic waves undergo attenuation, a reduction in signal amplitude away from the source. For logging devices this means radially away from the borehole wall. [[Acoustic_velocity_dispersion_and_attenuation|Signal attenuation]] results from the geometric spread of energy through:
  
All acoustic waves undergo attenuation, a reduction in signal amplitude away from the source. For logging devices this means radially away from the borehole wall. [[Acoustic velocity dispersion and attenuation|Signal attenuation]] results from the geometric spread of energy through:
 
 
*Reflection
 
*Reflection
 
*Refraction
 
*Refraction
Line 142: Line 166:
 
*Absorption by the medium through which the acoustic energy travels
 
*Absorption by the medium through which the acoustic energy travels
  
Attenuation, usually expressed in dB/ft, is characteristic of different materials and increases with frequency of the acoustic wave. Generally, attenuation is large in slow formations and very small to negligible in fast formations. Because of these features, Stoneley waves are used to identify acoustic leakage away from the borehole that may be caused by formation permeability or the presence of fractures.  
+
Attenuation, usually expressed in dB/ft, is characteristic of different materials and increases with frequency of the acoustic wave. Generally, attenuation is large in slow formations and very small to negligible in fast formations. Because of these features, Stoneley waves are used to identify acoustic leakage away from the borehole that may be caused by formation permeability or the presence of fractures.
  
==References==
+
== References ==
<references>
 
<ref name="r1">Cheng, C.H., Paillet, F.L., and  Pennington, W.D. 1992. Acoustic-Waveform Logging--Advances In Theory and Application. ''The Log Analyst'' '''33''' (3): 239. SPWLA-1992-v33n3a2.</ref>
 
  
<ref name="r2">Coates, R., Kane, M., Chang, C. et al. 2000. Single-well Sonic Imaging: High-Definition Reservoir Cross-sections from Horizontal Wells. Presented at the SPE/CIM International Conference on Horizontal Well Technology, Calgary, Alberta, Canada, 6-8 November 2000. SPE-65457-MS. http://dx.doi.org/10.2118/65457-MS </ref>
+
<references />
  
<ref name="r3">Thomas, D.H. 1978. Seismic Applications of Sonic Logs. ''The Log Analyst'' '''19''' (1): 23–32.</ref>
+
== Noteworthy papers in OnePetro ==
  
<ref name="r4">Liner, C.L. Interpreting Seismic Data. 2000. ''Exploring for Oil and Gas Traps, Treatise of Petroleum Geology, Handbook of Petroleum Geology'' E.A. Beaumont, and N.H. Foster eds., Chap. 12, 12-13–12–17. Tulsa, Oklahoma: AAPG.</ref>
+
Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read
  
<ref name="r5">Bork, J. and Wood, L.C. 2001. Seismic Interpretation of Sonic Logs, paper INT 1.4. ''Expanded Abstracts'', 2001 Annual Meeting Technical Program, SEG, 510–513.</ref>
+
== External links ==
  
<ref name="r6">Box, R., and Lowrey, P. 2003. Reconciling Sonic Logs with Check-Shot Surveys; Stretching Synthetic Seismograms. ''The Leading Edge'' '''22''' (6): 510–517. http://dx.doi.org/10.1190/1.1587672</ref>
+
Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro
 
 
<ref name="r7">White, R.E. 2003. Tying Well-Log Synthetic Seismograms to Seismic Data: The Key Factors, paper W-3.7. ''Expanded Abstracts'', 2003 Annual Meeting Technical Program, SEG, 2449–2452.</ref>
 
 
 
<ref name="r8">Walls, J., Dvorkin, J., and Carr, M. 2004. Well Logs and Rock Physics in Seismic Reservoir Characterization. Presented at the Offshore Technology Conference, Houston, Texas, 3-6 May. OTC-16921-MS. http://dx.doi.org/10.4043/16921-MS </ref>
 
 
 
<ref name="r9">Pistre, V. et al. 2005. A Modular Wireline Sonic Tool for Measurements of 3D (Azimuthal, Radial, and Axial) Formation Acoustic Properties, paper P. ''Trans.'', 2005 Annual Logging Symposium, SPWLA, 1–13.</ref>
 
 
 
<ref name="r10">Hornby, B. 1989. Imaging of near‐borehole structure using full‐waveform sonic data. ''Geophysics'' '''54''' (6): 747–757. http://dx.doi.org/10.1190/1.1442702</ref>
 
 
 
<ref name="r11">Hornby, B.E. 1995. Use of Full-Wave Sonic Data to Image Near-Borehole Structural Features. ''Petroleum Geoscience'' '''1''' (2): 109–114.</ref>
 
 
 
<ref name="r12">Esmeroy, C. et al. 1997. Sonic Imaging—A Tool for High-Resolution Reservoir Description, paper BH 2.7. ''Expanded Abstracts'', 1997 Annual Meeting Technical Program, SEG, '''1''', 278–281.</ref>
 
  
<ref name="r13">Tang, X.-M. and Cheng, A. 2004. Quantitative Borehole Acoustic Methods. In ''Handbook of Geophysical Exploration, Seismic Exploration'', Vol. 24. Oxford, England: Pergamon Press (Elsevier).</ref>
+
== See also ==
 
 
<ref name="r14">Chabot, L. et al. 2001. Single-Well Imaging Using the Full Waveform of an Acoustic Sonic, paper BH 3.7. ''Expanded Abstracts'', 2001 Annual Meeting Technical Program, SEG, 420–423.</ref>
 
 
 
<ref name="r15">Yamamoto, H., Watanabe, S., Koelman, J.M.V. et al. 2000. Borehole Acoustic Reflection Survey Experiments in Horizontal Wells for Accurate Well Positioning. Presented at the SPE/CIM International Conference on Horizontal Well Technology, Calgary, Alberta, Canada, 6-8 November 2000. SPE-65538-MS. http://dx.doi.org/10.2118/65538-MS </ref>
 
 
 
<ref name="r16">Tang, X.M. 2004. Imaging Near-Borehole Structure Using Directional Acoustic-Wave Measurement. ''Geophysics'' '''69''' (6): 1378–1386. http://dx.doi.org/10.1190/1.1836812</ref>
 
 
 
<ref name="r17">Zheng, Y., and Tang, X. 2005. Imaging Near-Borehole Structure Using Acoustic Logging Data with Prestack F-K Migration, paper BG 2. ''Expanded Abstracts'', 2005 Annual Meeting Technical Program, SEG, 360–363.</ref>
 
 
 
<ref name="r18">Paillet, F.L. and Cheng, C.H. 1991. ''Acoustic Waves in Boreholes'', 1–264. Boca Raton, Florida: CRC Press.</ref>
 
 
 
<ref name="r19">Mavko, G., Mukerji, T., and Dvorkin, J. 1998. ''The Rock Physics Handbook—Tools for Seismic Analysis in Porous Media'', 1-329. Cambridge, England: Cambridge University Press.</ref>
 
 
 
<ref name="r20">Hearst, J.R., Nelson, P.H., and Paillet, F.L. 2000. Acoustic Logging, ''Well Logging for Physical Properties'', second edition, Chap. 8, 257–303. New York City: Wiley and Sons Inc.</ref>
 
 
 
<ref name="r21">Cheng, C.H. and Toksoz, M.N. 1983. Determination of Shear Wave Velocities in ‘Slow’ Formation, paper V, ''Trans.'', 1983 Annual Logging Symposium, Soc. of Professional Well Log Analysts (SPWLA) 1–18.</ref>
 
 
 
<ref name="r22">Valero, H.P., Peng, L., Yamamoto, M. et al. 2004. Processing of Monopole Compressional In Slow Formation. Presented at the SEG Annual Meeting, Denver, Colorado, 10-15 October.</ref>
 
</references>
 
 
 
==Noteworthy papers in OnePetro==
 
Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read
 
 
 
==External links==
 
Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro
 
  
==See also==
+
[[Acoustic_logging_tools|Acoustic logging tools]]
[[Acoustic logging tools]]
 
  
[[Advanced acoustic data analysis]]
+
[[Advanced_acoustic_data_analysis|Advanced acoustic data analysis]]
  
[[Compressional and shear velocities]]
+
[[Compressional_and_shear_velocities|Compressional and shear velocities]]
  
[[Rock acoustic velocities and porosity]]
+
[[Rock_acoustic_velocities_and_porosity|Rock acoustic velocities and porosity]]
  
[[Rock acoustic velocities and pressure]]
+
[[Rock_acoustic_velocities_and_pressure|Rock acoustic velocities and pressure]]
  
[[Rock acoustic velocities and temperature]]
+
[[Rock_acoustic_velocities_and_temperature|Rock acoustic velocities and temperature]]
  
[[Rock acoustic velocities and in-situ stress]]
+
[[Rock_acoustic_velocities_and_in-situ_stress|Rock acoustic velocities and in-situ stress]]
  
[[Permeability estimation with Stoneley waves]]
+
[[Permeability_estimation_with_Stoneley_waves|Permeability estimation with Stoneley waves]]
  
[[PEH:Acoustic Logging]]
+
[[PEH:Acoustic_Logging]]
 +
[[Category:5.6.1 Open hole or cased hole log analysis]]

Latest revision as of 10:37, 24 June 2015

Petroleum applications of acoustic-wave-propagation theory and physics include both:

  • Surface-geophysical methods
  • Borehole-geophysical methods

Acoustic logging is a subset of borehole-geophysical acoustic techniques.

Historically, the primary and the most routine uses of acoustic logs in reservoir engineering have been:

Continuing developments in tool hardware and in interpretation techniques have expanded the utility of these logs in formation evaluation and completion (fracture) design and evaluation.

Overview

A virtual explosion in the volume of acoustic research conducted over the past 20 years has resulted in significant advances in the fundamental understanding of downhole acoustic measurements. These advances, in turn, have greatly influenced practical logging technology by allowing logging-tool designs to be optimized for specific applications.[1]

Acoustic-wave data-acquisition methods cover a broad range of scales from millimeters to hundreds of meters (Fig. 1[2]). Table 1 lists other common surface- and borehole-geophysical methods.

Borehole acoustic-logging measurements are used in a wide variety of geophysical, geological, and engineering applications and play an important role in the following undertakings (Table 2):

  • Evaluating reservoirs
  • Reducing exploration and production risks
  • Selecting well locations
  • Designing completions
  • Increasing hydrocarbon recovery

Modern logging tools include conventional borehole-compensated (BHC) monopole devices as well as the newer array devices—both monopole and multipole (monopole/dipole)—and logging-while-drilling (LWD) acoustic services. These logging tools provide acoustic measurements in all borehole mud types (but not in air- or foam-filled boreholes) in vertical, deviated, and horizontal wells, in both open and cased hole. They are combinable with other logging devices and are available in a variety of sizes to accommodate a range of borehole and casing diameters. Specialized tool designs are used for cement and casing evaluation and borehole imaging.

Geophysical applications

The higher operating frequency of acoustic-logging tools and the smaller TR distances allows for higher-quality velocity data and finer vertical resolution than surface reflection techniques. Acoustic-velocity logs were originally developed for calibrating surface seismic velocities and reflectors. Acoustic-log interval travel time or transit time, Δt, can be summed, i.e., integrated, over the entire logged interval to provide the equivalent of seismic one-way time which is compared to borehole seismic surveys and reflection seismic two-way time.

Acoustic-log data are commonly calibrated using checkshot (velocity) or vertical seismic profile (VSP) surveys prior to use in geophysical applications. Data from these surveys, which use downhole receivers and surface acoustic sources, are used to adjust the log data for drift and borehole conditions and result in improved time-depth correlation. Acoustic-log data are combined with density-log data, to generate an impedance log that in turn is used to produce a synthetic seismogram. Synthetic seismograms are artificial seismic records that tie seismic time to log depth and are also used to match well-log quantities to seismic attributes for distinguishing primary seismic events (geologic structure and stratigraphy). It is possible, however, that a synthetic seismogram may not provide a very good match to the seismic field data. Disagreements commonly result from the differences scale and acquisition physics used in seismic and well-log measurement; for example[3][4][5][6][7]:

  • Operational frequency (wavelength)
  • Borehole condition
  • Angle of measurement (particularly in the presence of anisotropy)

Acoustic-log data provide a fundamental and essential element of modern seismic reservoir characterization.[8] See fundamentals of geophysics for more information on the determination and use of these types of analyses.

Near-well imaging

Acoustic data acquired using modern array tools can provide high-resolution (0.5 m), microscale "seismic" 2D and 3D images of structural features in the near-borehole region (10 to 15 m). Conventional seismic-processing techniques, including filtering and migration, are used to extract compressional and shear reflections from the acoustic data. The reflections are then used to image geological features near the borehole. This technique allows the imaging of (Fig. 2)[9][10][11][12][13][14][15][16][17]:

  • Bed boundaries
  • Thin beds (stringers)
  • Fractures
  • Faults in openhole and cased wells

Acoustic theory and wave propagation

The principles of borehole acoustic logging (and surface seismic methods) are based on the theory of wave propagation in an elastic medium, as detailed in several sources[18][19][20][13]. The oscillating motion generated by a sound source (transducer) in an elastic medium (rock formation) is called an elastic wave or acoustic wave (also called head or body waves). Wave theory predicts how an acoustic signal propagates through the borehole and formation. Snell’s law explains how the acoustic signal behaves at the velocity boundary separating the borehole and the formation, that is, how it is transmitted into the formation and back to the receivers. Elasticity is the property of matter that causes it to resist deformation in volume or shape. It is the elastic nature of rock formations that permits wave propagation. Acoustic waves have four measurable properties:

  • Velocity
  • Amplitude
  • Amplitude attenuation
  • Frequency

Acoustic logging tools are designed to measure one or more of these properties, with velocity (slowness) being the most common.

The waveform recorded at the logging tool’s receivers is a composite signal containing different energy modes, each with a different frequency, velocity, and amplitude. For borehole logging, the modes of primary interest (Fig. 3) are, in order of arrival:

  • Compressional
  • Shear
  • Stoneley (tube) waves

The waveform is recorded as acoustic amplitude as a function of time.

These waves are transmitted through the medium some distance from the origin of displacement. The particles of the medium do not travel with the wave, but only vibrate around their mean central position. Acoustic waves are classified according to the direction of particle displacement with respect to the direction of wave propagation as either:

  • Longitudinal (i.e., particle displacement is parallel to the direction of propagation)
  • Transverse (i.e., direction of particle displacement is perpendicular to the direction of propagation)

In acoustic logging:

  • The longitudinal wave is known as the compressional wave
  • The transverse wave is known as the shear wave

The presence of the borehole excites two additional acoustic energy modes, called guided waves:

  • Normal (pseudo-Rayleigh)
  • Tube (Stoneley) waves

Acoustic-wave velocity is controlled by a number of factors:

The rock’s mechanical properties, elastic dynamics, and density are a constant for a particular homogeneous and isotropic material. Acoustic-wave velocity can be related to rock elastic properties through three constants of:

  • Proportionality
  • Elastic moduli (e.g., Young’s, shear, and bulk)
  • Poisson’s ratio

This serves as the basis for mechanical-property evaluation by acoustic logs. In reality, most petroleum reservoirs contain varying pore sizes, pore fill (e.g., clays), fractures, etc. and consequently, are neither truly isotropic nor homogeneous. Furthermore, in fluid-saturated rocks, these acoustic properties also depend on the type and volume of fluids present.

Compressional waves

Compressional (P, primary, or pressure) waves are longitudinal waves that are transmitted through an elastic formation by compression or pressure. Particle motion is parallel to the direction of wave propagation (Fig. 4). They can travel through solids, liquids, and gases and are the fastest wave type—they represent the acoustic first arrival. Of all acoustic wave types, they are the most reliable because they are least affected by:

  • Faults
  • Unconsolidated formations
  • Borehole fluids

The wave is transmitted by both the rock matrix (i.e., the framework) and the fluid present in the pore throats. A compression, together with an adjacent rarefaction preceding or following it, constitutes a complete cycle. The distance between complete cycles is called the wave length and the number of cycles propagating through a point in the medium per unit time is the frequency. The velocity of elastic-wave propagation in an isotropic homogeneous medium can be derived from a combination of the theory of elasticity with Newton’s law of motion. Compressional-wave velocity (or travel time) is a function of the density and elasticity of the medium and is a constant for a given material.

Shear and borehole flexural waves

Shear (S, secondary) waves are transverse waves that are transmitted by lateral displacement of particles in a rigid elastic formation. Particle motion is perpendicular to the direction of motion (Fig. 4). Normally, shear waves are the second arrival in an acoustic wave train. In most reservoir rocks, shear waves generally have higher amplitudes than compressional waves but lower velocities, by as much 40 to 50%. There are two types of borehole shear waves—direct and indirect, also known as refracted or induced. Indirect shear waves are induced in a formation through a process known as mode conversion in which some of the compressional energy is transferred from the borehole fluid into the rock formation. Monopole transmitters generate these indirect shear waves while dipole transmitters generate direct shear waves by inducing a flexural (asymmetric mode) in the borehole. Shear-wave propagation requires a medium that has shear strength (rigidity). Consequently, shear waves can only travel in solids, not in liquids or gas. In liquids and gas, the shear head-wave generated within the formation is converted into a compressional wave and propagated back across the borehole fluid to the acoustic receivers as a later-arriving compressional wave.

Unconsolidated or poorly consolidated sandstones ("soft" or "slow" rocks) are less rigid and more compressible than well-consolidated ("hard" or "fast") rocks. When the formation shear-wave velocity is less than the acoustic velocity of the borehole fluid (Vs < Vf), a rock formation is called "slow." There is no refracted shear-wave from monopole devices in slow formations and low-frequency dipole transmission and reception is required to adequately detect low-frequency flexural arrivals for the shear-wave slowness determination. However, if a monopole-array tool is used in these conditions, a shear-wave slowness can be estimated from Stoneley-wave velocity dispersion.[21] In very slow formations, where Vc < Vf, special processing may be required to extract the formation compressional signal.[22]

Flexural-wave velocity varies with frequency—a phenomenon called dispersion. In contrast, the compressional and shear headwaves generated by monopole sources are generally not dispersive. At very low frequencies, the flexural wave travels at the formation shear velocity. This dispersion effect diminishes as the wavelength of the flexural-wave increases and is generally minimal when the wavelength is at least three times the borehole diameter. Fast formations exhibit a center frequency slightly greater than 3 kHz, while slow formations exhibit a center frequency of ≈ 1 kHz, or less. The received frequency spectrum of a dipole array is a function of:

  • Transmitter frequency
  • Rock properties
  • Borehole size

Modern dipole transmitters are broadband transmitters, i.e., they operate over a range of frequencies, to account for dispersion and to accommodate different formation types.

Stoneley waves

Stoneley (tube) waves are high-amplitude guided waves that are generated by a radial (symmetric) flexing of the borehole as the acoustic energy passes from the borehole fluid into the rock formation. They propagate at low frequencies along the fluid-rock interface at the borehole wall; hence, they are sensitive to the rock properties adjacent to the borehole wall. They are the slowest acoustic mode. They can be measured in both open and cased boreholes, but in cased holes Stoneley-wave features are primarily controlled by the casing rigidity. Similarly to shear waves, Stoneley waves are also dispersive; i.e., wave velocity varies with frequency—the amount of dispersion is related to formation rock properties. However, Stoneley waves are notable for several special properties:

  • There is no cut-off frequency
  • Dispersion is very mild
  • For all frequencies, Stoneley-wave velocity is less than fluid velocity
  • Group velocity nearly equals phase velocity over the frequency range

All acoustic waves undergo attenuation, a reduction in signal amplitude away from the source. For logging devices this means radially away from the borehole wall. Signal attenuation results from the geometric spread of energy through:

  • Reflection
  • Refraction
  • Scattering
  • Absorption by the medium through which the acoustic energy travels

Attenuation, usually expressed in dB/ft, is characteristic of different materials and increases with frequency of the acoustic wave. Generally, attenuation is large in slow formations and very small to negligible in fast formations. Because of these features, Stoneley waves are used to identify acoustic leakage away from the borehole that may be caused by formation permeability or the presence of fractures.

References

  1. Cheng, C.H., Paillet, F.L., and Pennington, W.D. 1992. Acoustic-Waveform Logging--Advances In Theory and Application. The Log Analyst 33 (3): 239. SPWLA-1992-v33n3a2.
  2. 2.0 2.1 2.2 Coates, R., Kane, M., Chang, C. et al. 2000. Single-well Sonic Imaging: High-Definition Reservoir Cross-sections from Horizontal Wells. Presented at the SPE/CIM International Conference on Horizontal Well Technology, Calgary, Alberta, Canada, 6-8 November 2000. SPE-65457-MS. http://dx.doi.org/10.2118/65457-MS
  3. Thomas, D.H. 1978. Seismic Applications of Sonic Logs. The Log Analyst 19 (1): 23–32.
  4. Liner, C.L. Interpreting Seismic Data. 2000. Exploring for Oil and Gas Traps, Treatise of Petroleum Geology, Handbook of Petroleum Geology E.A. Beaumont, and N.H. Foster eds., Chap. 12, 12-13–12–17. Tulsa, Oklahoma: AAPG.
  5. Bork, J. and Wood, L.C. 2001. Seismic Interpretation of Sonic Logs, paper INT 1.4. Expanded Abstracts, 2001 Annual Meeting Technical Program, SEG, 510–513.
  6. Box, R., and Lowrey, P. 2003. Reconciling Sonic Logs with Check-Shot Surveys; Stretching Synthetic Seismograms. The Leading Edge 22 (6): 510–517. http://dx.doi.org/10.1190/1.1587672
  7. White, R.E. 2003. Tying Well-Log Synthetic Seismograms to Seismic Data: The Key Factors, paper W-3.7. Expanded Abstracts, 2003 Annual Meeting Technical Program, SEG, 2449–2452.
  8. Walls, J., Dvorkin, J., and Carr, M. 2004. Well Logs and Rock Physics in Seismic Reservoir Characterization. Presented at the Offshore Technology Conference, Houston, Texas, 3-6 May. OTC-16921-MS. http://dx.doi.org/10.4043/16921-MS
  9. Pistre, V. et al. 2005. A Modular Wireline Sonic Tool for Measurements of 3D (Azimuthal, Radial, and Axial) Formation Acoustic Properties, paper P. Trans., 2005 Annual Logging Symposium, SPWLA, 1–13.
  10. Hornby, B. 1989. Imaging of near‐borehole structure using full‐waveform sonic data. Geophysics 54 (6): 747–757. http://dx.doi.org/10.1190/1.1442702
  11. Hornby, B.E. 1995. Use of Full-Wave Sonic Data to Image Near-Borehole Structural Features. Petroleum Geoscience 1 (2): 109–114.
  12. Esmeroy, C. et al. 1997. Sonic Imaging—A Tool for High-Resolution Reservoir Description, paper BH 2.7. Expanded Abstracts, 1997 Annual Meeting Technical Program, SEG, 1, 278–281.
  13. 13.0 13.1 Tang, X.-M. and Cheng, A. 2004. Quantitative Borehole Acoustic Methods. In Handbook of Geophysical Exploration, Seismic Exploration, Vol. 24. Oxford, England: Pergamon Press (Elsevier).
  14. Chabot, L. et al. 2001. Single-Well Imaging Using the Full Waveform of an Acoustic Sonic, paper BH 3.7. Expanded Abstracts, 2001 Annual Meeting Technical Program, SEG, 420–423.
  15. Yamamoto, H., Watanabe, S., Koelman, J.M.V. et al. 2000. Borehole Acoustic Reflection Survey Experiments in Horizontal Wells for Accurate Well Positioning. Presented at the SPE/CIM International Conference on Horizontal Well Technology, Calgary, Alberta, Canada, 6-8 November 2000. SPE-65538-MS. http://dx.doi.org/10.2118/65538-MS
  16. Tang, X.M. 2004. Imaging Near-Borehole Structure Using Directional Acoustic-Wave Measurement. Geophysics 69 (6): 1378–1386. http://dx.doi.org/10.1190/1.1836812
  17. Zheng, Y., and Tang, X. 2005. Imaging Near-Borehole Structure Using Acoustic Logging Data with Prestack F-K Migration, paper BG 2. Expanded Abstracts, 2005 Annual Meeting Technical Program, SEG, 360–363.
  18. Paillet, F.L. and Cheng, C.H. 1991. Acoustic Waves in Boreholes, 1–264. Boca Raton, Florida: CRC Press.
  19. Mavko, G., Mukerji, T., and Dvorkin, J. 1998. The Rock Physics Handbook—Tools for Seismic Analysis in Porous Media, 1-329. Cambridge, England: Cambridge University Press.
  20. Hearst, J.R., Nelson, P.H., and Paillet, F.L. 2000. Acoustic Logging, Well Logging for Physical Properties, second edition, Chap. 8, 257–303. New York City: Wiley and Sons Inc.
  21. Cheng, C.H. and Toksoz, M.N. 1983. Determination of Shear Wave Velocities in ‘Slow’ Formation, paper V, Trans., 1983 Annual Logging Symposium, Soc. of Professional Well Log Analysts (SPWLA) 1–18.
  22. Valero, H.P., Peng, L., Yamamoto, M. et al. 2004. Processing of Monopole Compressional In Slow Formation. Presented at the SEG Annual Meeting, Denver, Colorado, 10-15 October.

Noteworthy papers in OnePetro

Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read

External links

Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro

See also

Acoustic logging tools

Advanced acoustic data analysis

Compressional and shear velocities

Rock acoustic velocities and porosity

Rock acoustic velocities and pressure

Rock acoustic velocities and temperature

Rock acoustic velocities and in-situ stress

Permeability estimation with Stoneley waves

PEH:Acoustic_Logging