Applied Geophysics: Seismic Methods

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Questions and Answers

What is stress represented by in the broad sense?

A force, called traction, acting on a finite area occupying an arbitrary position within the medium.

What is the limiting value of the ratio of a force acting on an elementary area, as the area diminishes to zero?

The stress (T), defined as: T = lim (F/ΔA)

What are the components of stress (T) that can be resolved into, and what do they represent?

The normal component (Tz), and two tangential components (Tx and Ty), representing normal stress and shearing stresses, respectively.

What is the normal component of stress (T) also known as?

The normal stress or dilatational or pressure stress. Signup and view all the answers

How many stress components are needed to completely define the stress at a given point?

Nine components, which constitute the stress tensor at that point. Signup and view all the answers

What is the significance of the nine stress components in describing the stress system within a body?

These components completely define the stress at a given point, providing a detailed understanding of the stress system within a body. Signup and view all the answers

What is the role of the elementary area (ΔA) in the definition of stress?

The elementary area (ΔA) is the area on which the force (F) acts, and it diminishes to zero in the limiting definition of stress. Signup and view all the answers

What is the importance of resolving the stress (T) into its components?

It enables the identification of normal and tangential components, which are essential for understanding the stress system within a body. Signup and view all the answers

What is the name of the strains that involve purely translational displacement?

Compressional or dilatational strain (principal strains) Signup and view all the answers

What is the name of the strains that involve purely rotational deformation?

Shear strain Signup and view all the answers

What are the three types of strain components mentioned in the text?

exx, eyy, ezz and exy, exz, eyz Signup and view all the answers

What is the approximate seismic wavelength for a 30Hz frequency at a speed of 1830m/S?

1830m Signup and view all the answers

What is an example of a no-strain change?

Rigid body-translation and rotation Signup and view all the answers

What is the range of wavelengths for typical speech sound waves?

25mm to 17m Signup and view all the answers

What is the name of the types of strains that involve a decrease in volume?

Compression or bulk contraction Signup and view all the answers

What is the result of an external force on an elastic medium?

Creation of internal opposing forces that resist deformation Signup and view all the answers

What is the name of the types of strains that involve an increase in length?

Tension Signup and view all the answers

What type of changes are created in an elastic medium due to an external force?

Changes in volume and/or shape Signup and view all the answers

What is the figure number that shows types of simple strains and no-strain changes?

Fig.5 Signup and view all the answers

Who is the author of the reference cited in the text?

Richter Signup and view all the answers

What is the property of an elastic medium that allows it to return to its original condition after the removal of an external force?

Elasticity Signup and view all the answers

What is the condition under which rock media in nature are considered perfectly elastic?

Provided that the changes are small Signup and view all the answers

What is the typical frequency of seismic waves in the context of applied geophysics?

30Hz or 60Hz Signup and view all the answers

What is the purpose of understanding seismic wavelengths in the context of applied geophysics?

To appreciate the size of seismic wavelengths Signup and view all the answers

What is the primary goal of a petroleum geoscientist specialist in fulfilling oil and gas industrial needs?

To evaluate the suitability of geophysical techniques for hydrocarbon resource exploration through methodology selections, acquisition designs and processing for specific geological situations. Signup and view all the answers

What is the significance of CLO2 in the context of hydrocarbon resource exploration?

Assessing the advantages and limitations of geophysical techniques in hydrocarbon resource exploration. Signup and view all the answers

What is the key capability required for PO2 in petroleum geoscience?

Demonstrating continuing and advanced knowledge in petroleum geoscience and having the capabilities to further develop or use these in new situations or multi-disciplinary context. Signup and view all the answers

What is the primary objective of PO3 in geology, geophysics, and reservoir?

Analyzing and evaluating critically problems in geology, geophysics, and reservoir, particularly in situations with limited information, and to provide solutions through the application of appropriate tools and techniques. Signup and view all the answers

What is the role of research evidence in petroleum geoscience according to PO5?

Appraising available information and research evidence in petroleum geoscience and applying it in the engineering context. Signup and view all the answers

What is the focus of PEO2 in terms of sustainability?

Industry leaders with integrity towards a sustainable future. Signup and view all the answers

What is the characteristic of a body that exhibits a proportional strain under stress?

elastic body Signup and view all the answers

What is the term used to describe the behavior of a body beyond the elastic limit, where deformation becomes irrecoverable?

plastic Signup and view all the answers

What is the point at which a body can no longer sustain the applied stress and breaks up?

rupture point Signup and view all the answers

What mathematical equation governs the linear stress-strain relationship in an isotropic and elastic body under small strain?

Hooke's law Signup and view all the answers

What is the term used to describe the limit beyond which the material may still be elastic, but with no more linear relationship?

elastic limit Signup and view all the answers

What type of body exhibits linear stress-strain behavior up to a certain stress limit?

perfectly elastic body Signup and view all the answers

What is the characteristic of a body under increasing stress, where the deformation becomes large with decreasing stress?

plastic zone Signup and view all the answers

What is the type of body that exhibits a linear stress-strain relationship under increasing stress up to a certain point?

ductile solid-body Signup and view all the answers

Study Notes

Course Overview

The course aims to equip students with knowledge and skills in applied geophysics, specifically in hydrocarbon resource exploration.
Course learning outcomes (CLOs) include evaluating the suitability of geophysical techniques, assessing their advantages and limitations, and appraising the sustainability of emerging techniques.

Seismic Waves

Seismic waves have wavelengths, e.g., 30Hz @ 1830m/S, or 60Hz @ 3660m/S, which are significantly longer than typical speech sound waves (25mm to 17m).
Seismic waves are created by applying an external force to an elastic medium, causing internal opposing forces that resist deformations and return to their original condition after the force is removed.
Rocks in nature are considered perfectly elastic, meaning they resist changes in volume and shape and return to their original condition after removal of the external force.

Theory of Elasticity

Elasticity is the property of resisting changes in volume and shape and returning to original conditions after removal of the external force.
Stress is a force acting on a finite area within a medium, defined as the limiting value of the ratio of a force (F) acting on an elementary area (ΔA) that is diminishing to zero.
Stress can be resolved into components parallel and perpendicular to the area, including normal stress (Tz) and tangential or shearing stresses (Tx and Ty).

Stress and Strain

The stress system within a body is completely defined by nine stress components, which constitute the stress tensor at a given point.
Strain components (eab) can be written down as follows: Group 1 (exx, eyy, ezz) involves purely translational displacement resulting in compressional or dilatational strain, and Group 2 (exy, exz, eyz) involves purely rotational deformation resulting in shear strain.
Common types of strains include compression, bulk contraction, tension, and shear strains.

Types of Strain

Fig. 5 shows simple types of elastic deformation (strain) and no-strain changes, such as rigid body translation and rotation.
The linear stress-strain relationship is governed by Hooke's law, which describes the behavior of perfectly elastic bodies under small strain.

Elastic and Plastic Behavior

Bodies under stress exhibit deformation depending on the applied load and physical properties.
Elastic bodies exhibit a proportional strain, and perfectly elastic bodies exhibit a linear relationship.
Beyond the elastic limit, the deformation becomes irrecoverable, and the body behavior is described as plastic.
The behavior of a ductile solid-body under an increasing extensional stress is shown in Fig. 9.

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Description

This course covers the fundamentals of geophysics, focusing on seismic methods and wave principles in hydrocarbon resource exploration. Learn about methodology selection, acquisition designs, and processing techniques for specific geological situations.