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Geo 397 FINAL EXAM - Apr 24 > misc test ques > Flashcards

misc test ques Flashcards

1
Q

true or false

p wave velocity is approx 2x S wave velocity

A

TRUE

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2
Q

true or false

4D surveys are useful for monitoring reservoir production over a time period

A

TRUE

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3
Q

true or false

wide azimuth surveys are characterized by a large variation in shot and receiver azimuths over narrow azimuth surveys

A

TRUE

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4
Q

true or false

shear vibrators are used to generate sheer waves for 3C land surveys

A

TRUE

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5
Q

true or false

each component of a multi-component data set is recorded on a separate seismic channel

A

TRUE

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6
Q

What’s the acronym mean ?

CCP

A

Common Conversion Point

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7
Q

What’s the acronym mean ?

CMP

A

Common Mid Point

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8
Q

What’s the acronym mean?

VSP

A

Vertical Seismic Profile

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9
Q

What does the acronym mean ?

PSv

A

Pwave to vertical Swave conversion

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10
Q

What’s the acronym mean?

CDP

A

Common Depth Point

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11
Q

Define 3C /4D

A

2 or 3 surveys done over time

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12
Q

Define azimuthal anisotropy

A

regional stress orientation

rocks fractured EW travels faster than NS

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13
Q

Define P/Z data

A

vertical component of particle velocity recorded from geophone is scaled and summed with pressure from receiver side water layer reverberations

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14
Q

Define speculative survey

A

Seismic survey taken by a service company. Later sold to an oil company who may have interest in that area.
aka multiclient survey

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15
Q

What are the 2 possible OBC acquisition geometries?

A

orthogonal

parallel

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16
Q

In MC acquisition, what are the 3 methods of cable deployment?

A

dragged cable
draped cable
dragged and draped

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17
Q

explain 2C acquisition

A

2 component
hydrophone P wave
geophone vertical
Marine

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18
Q

explain 4C acquisition

A

4 components
1 hydrophone P wave
3 geophones – 2 horizontal and 1 vertical

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19
Q

3 basic steps of C-wave data processing

A

Preprocessing of all components
P wave time and depth processing
C wave time and depth processing

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20
Q

what is the relationship between productivity and anisotropy ?

A

high well productivity when direction of the fracture is taken into consideration. Drill so oil flows in order of the fracture.

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21
Q

The horizontal component energy is transferred between 2 components - which are they ?

A

radial - SR direction

transverse - perpendicular to radial

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22
Q

List 2 processes commonly applied when processing VSP data

A

deconvolution
stack
mute
filter/scale

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23
Q

describe 2 differences seen between P wave and S wave section

A
  • P wave has a higher frequency content than S wave

- TWT of an event on a Pwave section is 1/2 that of same event on a S wave section because the Pwave travels faster

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24
Q

State 2 properties of P and S waves

A

P waves travel 2x faster than S waves

No S waves in liquids

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25
Q

What is surface consistent process

A

process in which location of shot and receiver is taken into consideration in the computation

26
Q

cross correlation

A

comparison of 2 different wavelets

in vibroseis produces zero phase wavelet by way of linear filter

27
Q

What are the 2 names given to velocity generated false structures ?

A

velocity sag

pull-up

28
Q

what 2 false structures do the velocity affects create ?

A

velocity sag produces false syncline

pull up produces false rollover

29
Q

What is the possible reason for the velocity affect in creating a false structure?

A

juxtaposition of high velocity one in footwall against low velocity zone in hanging wall

30
Q

List structural and stratigraphic features visible on coherence cube images ?

A

structural features – faults

stratigraphical features - reefs, river channels and deltas

31
Q

How are the seismic traces interrupted by faults, detected in the coherence cube?

A

discontinuity of trace to trace coherence producing delineation of low coherence along fault plane

32
Q

what does impedance represent ?

A

acoustic impedence – properties of the layer

33
Q

what does seismic amplitude represent ?

A

attribute of the layer boundaries

34
Q

list 4 surface consistent processes in the processing sequence

A

3D amplitude compensation
spiking deconvolution
refraction statics
reflection statics

35
Q

what are the 2 possibilities regarding migration domain and method of applicatioon

A 
Migration Domain (Time or Depth Domain)
Methods (1 pass or 2 pass)
36
Q

what is depth step ?

A

in time or depth

increment in which migration process is applied

37
Q

what is migration aperture?

A

larger the dip, the larger migration aperture. max range of movement for migration to take place

38
Q

what are migration velocities

A

stacking velocities slowed by 5-10%

39
Q

List difference between Post stack and Pre Stack Migration

A

PreStack Migration is performed on fully processed CDP gathers
Post Stack Migration is applied to stacked traces

40
Q

Why is pre-stack migration better than post-stack migration ?

A

trace amplitudes are migrated to proper bin prior to stacking

41
Q

List 4 types of velocity data incorporated into the 3d velocity cube of the Gulf of Mexico data

A

Vint
Post Stack 3D migration results
well data
VSP

42
Q

What are the 3 types of velocities and state where it is from

A

Vint - sonic log
Vavg - calculated
Vrms - calculated from Vint

43
Q

What’s the purpose of a match filter ?

A

match 2 data sets (shape and frequency)

44
Q

What are the 3 properties of a multiple?

A

slower velocity

polarity reversal

45
Q

why does a water bottom multiple alternate in polarity of the the wavelet ?

A

RC changes and becomes a negative value

46
Q

State a purpose of VSP

A

in-situ rock properties in depth

47
Q

List 5 types of VSP

A 
walkaway VSP
multi-azimuth VSP
zero offset VSP
3D vsp
cross-well VSP
48
Q

define inhomogenous

A

measure property inconsistent in XY direction

49
Q

define isotropic

A

sdfs

50
Q

define azimuthal anisotropy

A

seismic wave travels differently depending on the direction of fractures. EW travels faster than NS

51
Q

define S wave

A

shear wave

particle motion is perpendicular to propagation of wave

52
Q

list linear shot noise

A

ground roll
air waves
backscatter

53
Q

What’s the effect of summing or stacking data

A

increase coherent signal and reduce incoherence signal

54
Q

name 2 attributes of traces in a CMP bin that determines effectivement of attenuation of multiples or other noise types

A

offset

azimuth

55
Q

describe the seismic wave travel velocities with respect ot the direction of fractures

A

seismic wave travel velocities are faster along direction of the fracture and slower in orthogonal direction

56
Q

Specify 2 geophysical advantages using S wave or C wave data for seismic data intepretation

A

enhance reservoir characterization

57
Q

State 2 possible OBC acquisition geometries

A

parallel - shot and receivers are parallel to one another

orthogonal - used i you wish to illuminate - shot and receivers are orthogonal to one another

58
Q

what are free surface multiples ?

A

multiple with 1 or more reflections from the air-water interface

59
Q

What’s the purpose of VSP ?

A

match VSP with surface seismic to identify multiples

60
Q

Name some properties of multiples

A

periodic
multiple velocity is less than primary velocity
polarity reversal at air/water interface (marine only)

61
Q

what’s SUPERGATHER

A

CDP gather w summation of adjacent CDP gather

Geo 397 FINAL EXAM - Apr 24 (13 decks)

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