Rock Physics and Biot-Gassmann Equations Models Quiz

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What does AVO stand for in seismic analysis?

Amplitude Versus Offset (correct)

Amplitude Versus Angle

Angle Versus Offset

Angle Versus Amplitude

What is the relationship that AVO is based on?

Amplitude and offset

Seismic waves and CMP

Reflection coefficient and distance

Reflection coefficient and angle of incidence (correct)

What is the common point on the reflector between the source and receiver known as?

Common midpoint (CMP) (correct)

Midpoint reflector

Seismic gather point

Zero-incidence point

What describes the angle of incidence and reflection angle being zero in AVO analysis?

Zero-incidence Signup and view all the answers

What do increasing offset and incidence angles lead to in seismic traces?

Increased amplitude Signup and view all the answers

What does a seismic CMP gather consist of?

Traces with increasing offset and angles of incidence Signup and view all the answers

What does the AVO analysis focus on in seismic data?

Variation of amplitude observed at different angles or offsets Signup and view all the answers

When did AVO analysis become popular among geophysicists?

1980s Signup and view all the answers

Which seismic anomaly is described as an event brighter than others at the same stratigraphic level?

Bright spot Signup and view all the answers

What do the Zoeppritz equations govern in terms of seismic waves?

Amplitudes of different wave modes Signup and view all the answers

Which parameter affects the amplitude of reflected events according to Zoeppritz's equations?

Density Signup and view all the answers

What does the velocity of an S-wave depend on?

Shear modulus 𝜇 Signup and view all the answers

How does a P-wave affect the rock particles as it propagates through the material?

"Compresses" the rock Signup and view all the answers

Why does the bulk modulus K change significantly when the fluid in a rock is changed?

Due to a decrease in water saturation when gas is introduced. Signup and view all the answers

What effect does introducing gas into the pores have on the P-wave velocity of the rock?

Decreases P-wave velocity. Signup and view all the answers

How is S-wave velocity affected by a decrease in rock density due to gas saturant?

S-wave velocity slightly increases. Signup and view all the answers

Why is it important to study both P and S velocities simultaneously?

To differentiate between different lithologies. Signup and view all the answers

How can mode conversion be utilized in seismic surveys?

By interpreting amplitudes of P-waves as a function of offset. Signup and view all the answers

What is one way to record converted S-waves according to the text?

Utilizing three-component receivers in X, Y, and Z directions. Signup and view all the answers

Which method involves interpreting P-wave reflections at different offsets to extract S-wave type information?

AVO method Signup and view all the answers

What do the Zoeppritz Equations provide a complete theory for?

Amplitudes of reflected and transmitted waves at an interface Signup and view all the answers

How do Zoeppritz Equations help extract S-wave type information?

By analyzing bulk modulus changes Signup and view all the answers

Why is Poisson's ratio significant in distinguishing lithologies?

It can be expressed in terms of Vp and Vs ratios. Signup and view all the answers

Which weight in the Aki-Richards equation represents the amplitude at zero angle of incidence?

A Signup and view all the answers

In which range of angles does the second term in the Shuey approximation start to affect the reflection coefficient?

15°–30° Signup and view all the answers

What are the weights/parameters in the Fatti et al. formulation of the Aki-Richards equation?

c1, c2, c3 Signup and view all the answers

Which formulation of the Aki-Richards equation is particularly useful for extracting empirical information about the AVO effect?

A, B, C formulation Signup and view all the answers

What does the Shuey approximation eliminate in favor of using Poisson's ratio?

Vs and ∆Vs Signup and view all the answers

In the Three term AVO calculation, what do the weights A, B, and C represent?

Intercept, gradient, curvature Signup and view all the answers

What is the primary focus of the Fatti et al. formulation of the Aki-Richards equation?

Petrophysical properties evaluation Signup and view all the answers

What does the AVO Intercept represent in the context of seismic data analysis?

Acoustic impedance variations across layer boundary Signup and view all the answers

In AVO crossplotting, what does a data point in the negative intercept and positive gradient quadrant signify?

Hard event underneath the gas reservoir Signup and view all the answers

Which seismic analysis tool combines AVO theory with inversion techniques for enhanced reservoir discrimination?

AVO Inversion Signup and view all the answers

What do changes in AVO Intercept A correspond to across the layer boundary?

Acoustic impedance variations Signup and view all the answers

In AVO methodology, which group of methods is applied for a feasibility study to predict AVO responses?

Methods based on Rock Physics Modelling Signup and view all the answers

What elastic properties are used in AVO analysis to separate rocks with different types of saturation?

P-wave velocity and S-wave velocity Signup and view all the answers

In AVO crossplotting, what do data points in the pink zone signify?

Top of gas sand zone Signup and view all the answers

What method uses NMO-corrected gathers with an optimal processing sequence for analyzing AVO attributes?

Direct analysis methods Signup and view all the answers

What does Model A consist of in the context of the text?

Wet, or brine sand Signup and view all the answers

How does the presence of gas in sand affect the P-wave velocity compared to shale?

Lowers it below that of shale Signup and view all the answers

What happens to the density of sandstone with the presence of gas?

It decreases Signup and view all the answers

In AVO modeling, what are the input well logs used to represent rock properties?

P-wave velocity, Density, S-wave velocity, Poisson’s Ratio Signup and view all the answers

Which AVO attribute is calculated based on regression curves in AVO analysis?

Gradient Signup and view all the answers

What do Intercept and Gradient represent in AVO attributes?

Basic AVO attributes for each time sample Signup and view all the answers

What is represented by Sigma in the context of rock properties discussed in the text?

Poisson’s ratio Signup and view all the answers

In the comparison between two and three term methods in AVO modeling, what is evident about deviation at higher angles?

There is greater deviation at higher angles in the two term method. Signup and view all the answers

What does Model B consist of in the context provided?

Gas-saturated sand Signup and view all the answers

What kind of boundary does the model used in Zoeppritz equations assume?

Non-slip boundary Signup and view all the answers

Why aren't the Zoeppritz coefficients always completely accurate in explaining real seismic responses?

Due to the assumptions made in the model Signup and view all the answers

What did the approximations to the Zoeppritz equations aim to better show?

Information conveyed by changes in amplitude Signup and view all the answers

What are the three contrast variables expressed in the Aki-Richards approximation?

Delta rho over rho, delta Vp over Vp, delta Vs over Vs Signup and view all the answers

What is the main limitation of the Aki-Richards approximation?

Limited to interfaces with small contrasts and small incident angles Signup and view all the answers

What does a picked event at a given time on the 3 trace angle gather represent?

Aki-Richards reflectivity Signup and view all the answers

What is the sum of the three weighted reflectivities in the Aki-Richards linear equation?

( R_{theta} ) Signup and view all the answers

In which situation is the Aki-Richards equation much simplified?

( \theta = 0 ) Signup and view all the answers

What information does the Aki-Richards equation struggle to derive from reflectivity?

( VP/VS ) ratios Signup and view all the answers

What do authors use to create slightly different versions of the Aki-Richards approximation?

Different parameters and contrasts Signup and view all the answers