06 - Elastic properties

Question 1

Elastic materials deform …

Answer 1

when a force is applied and return to their original shape when the force is removed

Question 2

Young’s modulus

Answer 2

E = stress / strain

measure of the stiffness of a solid material.

Question 3

Poisson ratio v

Answer 3

v = - (dL* / L*) / (dL/L)

Question 4

Hooke’s law

sigma_ik

Answer 4

relationship between stress and strain

sigma_ik = C_iklm * strain_lm

Question 5

p-wave velocity v_p

Answer 5

v_p = sqrt( (lambda+2mü)/rho )

Question 6

s-wave velocity v_s

Answer 6

v_s = sqrt( mü/rho )

Question 7

Correlation of Poisson ratio to Velocityratio

Answer 7

v_p/v_s = sqrt( 2* (1-v)/(1-2*v) )

the larger v the larger p and s-wave difference

Question 8

Transmission technique

from transmitter ..

receiver..

visualizing ..
what?

Answer 8

..an ultrasonic pulse passes through sample

.. transform elastic wave into electrical signal

.. with an oscilloscope
the signal and travel time

Question 9

shear modulus of fluids and minerals

Answer 9

fluids: 0 -> no
Minerals: yes

Question 10

compressional modulus of fluids and minerals

Answer 10

all: yes
order: Gas, oil and water, minerals

(under specific conditions)

Question 11

p-wave velocity

slower to fast:

oil, water, air

Answer 11

air

oil

water

Question 12

Differences of s and p-wave velocities in Rocks

Answer 12

greater differences occur in:

Granite
Diorite
Gabbro
Ultramafic rocks
Basalt 
Eclogit

Question 13

p-wave velocity

slower to fast:

shale, sand&gravel, sandstone, all others

Answer 13

sand&gravel

shale

sandstone

all others

Question 14

velocity of igneous rocks

Answer 14

increases from felsic to mafic

Question 15

velocity in methamorphic rocks

Answer 15

anisotropy (gneiss schist)

-> greater velocity parallel to schistosity

Question 16

velocity in sedimentary/porous rocks

Answer 16

brad range

-> low velocity for porous gas bearing members

Question 17

ratio of the two wave velocities Vp/Vs or the Poisson’s ratio n is controlled mainly by …

Answer 17

rock type

pore fluid

Question 18

velocity with fracturing

Answer 18

velocity decreases
velocity show pressure dependence
anisotropic?

Question 19

Correlation of velocity with temperature

Answer 19

decreases with increasing temperature

Question 20

shear wave velocity and change of pore fluid

Answer 20

insensitive ( gas brine)

effect of clay more relevant!

Question 21

Five possible sources of seismic anisotropy

Answer 21

(1) aligned crystals,
(2) direct stress-induced anisotropy,
(3) lithological anisotropy (for example aligned grains),
(4) structural anisotropy (for example fine layering), and
(5) stress aligned crack-induced anisotropy.

Question 22

elastic properties below the critical porosity

Answer 22

rock skeleton dominated

grain contact behavior controls many effects

Question 23

elastic properties above the critical porosity

Answer 23

fluid dominated

particles are embedded in the fluid as a suspension

Question 24

Sonic logging

with ..

using ..

measure ..

Answer 24

sound wave

piezoelectric transmitter and receiver

interval transit time,
which is typically a function of lithology and rock texture but particularly porosity

Question 25

Borehole televiewers

measures ..

how..

Answer 25

amplitude and transit time at one of two frequencies

Short bursts of acoustic energy are emitted by a rotating transducer in pulse-echo mode