Rock Physics and Anisotropy in Seismic Interpretation

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Questions and Answers

What has led to a revision of the industry's attitude towards anisotropy?

Rapid development of computer technologies and seismic methods

Which type of anisotropy is usually considered in reservoir studies?

HTI anisotropy

What is the most striking example of HTI anisotropy in reservoir studies?

Vertical fractures

How are smaller fractures with sub-seismic lengths that cannot be directly imaged usually inferred from seismic data?

By applying effective media theories Signup and view all the answers

Which method is used to describe the reservoir in advanced QI techniques?

4D reservoir characterization Signup and view all the answers

What is one of the techniques introduced in this module according to the text?

Azimuthal AVO and inversion of broadband seismic data Signup and view all the answers

What does the use of azimuthal AVO analysis help predict?

The presence of fractures Signup and view all the answers

How does increasing the frequency content to the higher end of the spectrum affect the seismic signal?

Narrows the signal Signup and view all the answers

What is one advantage of including anisotropy information in a reservoir model?

Improved production history matching Signup and view all the answers

What is one benefit of variable-depth streamer acquisition over conventional streamer profiles?

Reduction of water surface noise Signup and view all the answers

Why are low frequencies often absent in conventional seismic data?

Constraints in seismic acquisition Signup and view all the answers

What characterizes the interface property in anisotropic gradient analysis?

Fracture density Signup and view all the answers

In seismic reservoir characterization, why is broadband seismic data particularly valuable?

It fills the low-frequency gap Signup and view all the answers

What helps validate the results obtained from different azimuthal approaches in seismic analysis?

Wells with imaging logs like FMI Signup and view all the answers

"Frequency, in addition to amplitudes, provides valuable information". What does increasing frequency range at the lower end minimize?

"Sidelobes" Signup and view all the answers

How does extending frequency range at the lower end help address challenges related to sidelobes in seismic data?

Minimizes sidelobes and uncertainties introduced by them Signup and view all the answers

What geomechanical parameters can be inferred by analyzing seismic anisotropy?

Rock stiffness, stress orientation, and fracture density Signup and view all the answers

In seismic studies, HTI anisotropy is usually associated with:

Vertical fractures Signup and view all the answers

Why do seismic wave velocities vary with direction in the presence of aligned vertical fractures?

As a result of the alignment of fractures Signup and view all the answers

What does Azimuthal Velocity Analysis help define in seismic studies?

Stacking velocities Vfast and Vslow Signup and view all the answers

How does Azimuthal AVO analysis differ from conventional AVO analysis?

It studies amplitude variations with offset for different azimuths Signup and view all the answers

What can be inferred from velocity inconsistencies between isotropic inversion and azimuthal inversion measurements?

The alignment of fractures Signup and view all the answers

Why has the industry's attitude towards studying seismic anisotropy changed over time?

Due to advances in computer technologies and seismic methods Signup and view all the answers

What is the primary difference between PP and PS waves in terms of velocity?

PP waves travel up with faster velocity than PS waves. Signup and view all the answers

Which type of seismic wave typically exhibits higher frequencies?

P-waves Signup and view all the answers

Why is it important to align or register PS seismic to PP seismic prior to inversion?

To compare the amplitudes of both PP and PS volumes Signup and view all the answers

What is the main advantage of utilizing 4D seismic data in reservoir characterization?

Monitoring changes in reservoir properties over time Signup and view all the answers

What does joint inversion of PP-PS data enable in terms of model constraining?

It integrates independent information about S-waves for improved accuracy Signup and view all the answers

How do azimuthal seismic data contribute to reservoir management?

By estimating anisotropic parameters and detecting fractures Signup and view all the answers

In seismic inversion, why is the presence of low-frequency data in broadband datasets important?

It helps in defining the reservoir's geometry more accurately. Signup and view all the answers

What is one of the key benefits of using PS data in seismic studies?

It enables improved modeling by constraining elastic properties estimation. Signup and view all the answers

What role does mode conversion play in seismic studies?

It generates both P and S waves. Signup and view all the answers

How does broadband seismic data differ from conventional seismic data?

It contains low-frequency components. Signup and view all the answers

What is the significance of studying PP data for gaining insights into S-wave velocity?

Helps in analyzing amplitude variations with offsets. Signup and view all the answers

Why are PS waves preferred over PP waves for studying subsurface beneath gas clouds?

PS waves are less affected by gas absorption. Signup and view all the answers

What is the primary advantage of joint PP-PS tomography?

Provides an initial model for inversion. Signup and view all the answers

Why is the presence of low-frequency reflectivity crucial for inversion algorithms?

It helps improve the delineation of pay intervals. Signup and view all the answers

What effect does mode conversion have on seismic signal interference?

It increases interference by affecting PP data travel times. Signup and view all the answers

What geomechanical parameters can be inferred by analyzing seismic anisotropy?

Stress level and fracture orientation Signup and view all the answers

How do seismic wave velocities typically vary in the presence of aligned vertical fractures?

They are fastest parallel to the fractures Signup and view all the answers

What insight can be gained from studying variations in velocity or amplitude as functions of azimuth?

Understanding seismic anisotropy Signup and view all the answers

What challenges are associated with conducting repeat 4D seismic surveys for reservoir monitoring?

Maintaining consistent data quality Signup and view all the answers

How can changes in fluid saturation affect the elastic properties of rocks in a reservoir?

Altering porosity Signup and view all the answers

What information does a significant improvement in correspondence between P-wave velocities obtained indicate?

Improvement in seismic anisotropy estimation Signup and view all the answers

Why can comparing Vp obtained from isotropic inversion with Vp measured in a horizontal well reveal inconsistencies?

Because of drilling direction relative to fractures Signup and view all the answers

What is the primary challenge of integrating time-lapse seismic data with other reservoir data?

Sophisticated interpretation techniques Signup and view all the answers

What do changes in the fluid saturation, pressure, porosity, and temperature of a reservoir result in?

Changes in the elastic properties of rocks. Signup and view all the answers

Why is it essential to ensure consistency in acquisition parameters and data quality between baseline and repeat surveys in 4D seismic monitoring?

To accurately analyze changes over time. Signup and view all the answers

Study Notes

Advanced QI Methods

Introduce 4D reservoir characterization, Azimuthal AVO, and Inversion
Inversion of broadband seismic data and PP-PS joint inversion

Seismic Anisotropy

Study of seismic anisotropy gained importance since the 1950s
Effects of anisotropy were initially ignored in production work due to limitations of techniques
Development of computer technologies and seismic methods led to a revision of the industry's attitude towards anisotropy
HTI (horizontal transverse isotropy) anisotropy is considered in reservoir studies, often represented as vertical inhomogeneities of an isotropic medium
Example: vertical fractures

Measuring Seismic Anisotropy

Measure travel times and amplitudes of waves propagating in various directions
Study variations in velocity or amplitude as functions of azimuth to gain insights into seismic anisotropy

4D Seismic Reservoir Characterization

Changes in fluid saturation, pressure, porosity, and temperature of a reservoir result in changes in elastic properties of rocks, affecting the seismic response
4D seismic provides valuable insights into reservoir dynamics, essential for optimizing reservoir management and production strategies
Challenges of 4D seismic: maintaining signal stability, integrating with other reservoir data, and understanding complex relationships between seismic attributes and reservoir properties
Example: Draugen Field 4D Study, resolving uncertainties and forecasting an extension in plateau production

Azimuthal Velocity Analysis

Based on the effect of different times of arrival of the reflected wave for different azimuths
Estimates seismic anisotropy by defining the stacking velocities Vfast and Vslow and direction of Vfast
Corrects gathers with anisotropic NMO (normal moveout)

Azimuthal AVO Analysis

Studies amplitude variations with offset, also conducted for different azimuthal directions
Key results: anisotropic gradient Bani and direction of the plane of isotropy φiso
Bani is proportional to fracture density, allowing prediction of fracture presence

Inversion of Angle Stacks

Inverts angle stacks for different azimuths to obtain elastic properties, anisotropy coefficients, and azimuth as layer properties

Validating Results with Wells

Results of azimuthal approaches should be validated with wells using imaging logs like FMI (formation micro-imager)
Example: tight but fractured carbonate reservoir with low matrix permeability

Broadband Seismic

Provides valuable information, filling the low-frequency gap
Enables capturing of finer details and subtle features within subsurface geology, resulting in higher-resolution seismic images
Increases the accuracy and robustness of estimates of reservoir properties
Example: marine acquisition with variable-depth streamer acquisition to access full bandwidth

Joint PP-PS Inversion

Combines independent information about S-waves, further constraining the model
Leads to improved accuracy and reliability in the estimation of elastic properties
Enables enhanced reservoir properties analysis
Example: successful PP-PS project from offshore Vietnam

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Rock Physics and Anisotropy in Seismic Interpretation

Questions and Answers

What has led to a revision of the industry's attitude towards anisotropy?

Which type of anisotropy is usually considered in reservoir studies?

What is the most striking example of HTI anisotropy in reservoir studies?

How are smaller fractures with sub-seismic lengths that cannot be directly imaged usually inferred from seismic data?

Which method is used to describe the reservoir in advanced QI techniques?

What is one of the techniques introduced in this module according to the text?

What does the use of azimuthal AVO analysis help predict?

How does increasing the frequency content to the higher end of the spectrum affect the seismic signal?

What is one advantage of including anisotropy information in a reservoir model?

What is one benefit of variable-depth streamer acquisition over conventional streamer profiles?

Why are low frequencies often absent in conventional seismic data?

What characterizes the interface property in anisotropic gradient analysis?

In seismic reservoir characterization, why is broadband seismic data particularly valuable?

What helps validate the results obtained from different azimuthal approaches in seismic analysis?

"Frequency, in addition to amplitudes, provides valuable information". What does increasing frequency range at the lower end minimize?

How does extending frequency range at the lower end help address challenges related to sidelobes in seismic data?

What geomechanical parameters can be inferred by analyzing seismic anisotropy?

In seismic studies, HTI anisotropy is usually associated with:

Why do seismic wave velocities vary with direction in the presence of aligned vertical fractures?

What does Azimuthal Velocity Analysis help define in seismic studies?

How does Azimuthal AVO analysis differ from conventional AVO analysis?

What can be inferred from velocity inconsistencies between isotropic inversion and azimuthal inversion measurements?

Why has the industry's attitude towards studying seismic anisotropy changed over time?

What is the primary difference between PP and PS waves in terms of velocity?

Which type of seismic wave typically exhibits higher frequencies?

Why is it important to align or register PS seismic to PP seismic prior to inversion?

What is the main advantage of utilizing 4D seismic data in reservoir characterization?

What does joint inversion of PP-PS data enable in terms of model constraining?

How do azimuthal seismic data contribute to reservoir management?

In seismic inversion, why is the presence of low-frequency data in broadband datasets important?

What is one of the key benefits of using PS data in seismic studies?

What role does mode conversion play in seismic studies?

How does broadband seismic data differ from conventional seismic data?

What is the significance of studying PP data for gaining insights into S-wave velocity?

Why are PS waves preferred over PP waves for studying subsurface beneath gas clouds?

What is the primary advantage of joint PP-PS tomography?

Why is the presence of low-frequency reflectivity crucial for inversion algorithms?

What effect does mode conversion have on seismic signal interference?

What geomechanical parameters can be inferred by analyzing seismic anisotropy?

How do seismic wave velocities typically vary in the presence of aligned vertical fractures?

What insight can be gained from studying variations in velocity or amplitude as functions of azimuth?

What challenges are associated with conducting repeat 4D seismic surveys for reservoir monitoring?

How can changes in fluid saturation affect the elastic properties of rocks in a reservoir?

What information does a significant improvement in correspondence between P-wave velocities obtained indicate?

Why can comparing Vp obtained from isotropic inversion with Vp measured in a horizontal well reveal inconsistencies?

What is the primary challenge of integrating time-lapse seismic data with other reservoir data?

What do changes in the fluid saturation, pressure, porosity, and temperature of a reservoir result in?

Why is it essential to ensure consistency in acquisition parameters and data quality between baseline and repeat surveys in 4D seismic monitoring?

Study Notes

Advanced QI Methods

Seismic Anisotropy

Measuring Seismic Anisotropy

4D Seismic Reservoir Characterization

Azimuthal Velocity Analysis

Azimuthal AVO Analysis

Inversion of Angle Stacks

Validating Results with Wells

Broadband Seismic

Joint PP-PS Inversion

Studying That Suits You

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