misc test ques Flashcards by V R Marr

true or false

p wave velocity is approx 2x S wave velocity

TRUE

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true or false

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

TRUE

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true or false

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

TRUE

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true or false

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

TRUE

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true or false

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

TRUE

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What’s the acronym mean ?

CCP

Common Conversion Point

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What’s the acronym mean ?

CMP

Common Mid Point

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What’s the acronym mean?

VSP

Vertical Seismic Profile

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What does the acronym mean ?

PSv

Pwave to vertical Swave conversion

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What’s the acronym mean?

CDP

Common Depth Point

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Define 3C /4D

2 or 3 surveys done over time

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Define azimuthal anisotropy

regional stress orientation

rocks fractured EW travels faster than NS

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Define P/Z data

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

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Define speculative survey

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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What are the 2 possible OBC acquisition geometries?

orthogonal

parallel

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

dragged cable
draped cable
dragged and draped

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explain 2C acquisition

2 component
hydrophone P wave
geophone vertical
Marine

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explain 4C acquisition

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

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3 basic steps of C-wave data processing

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

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what is the relationship between productivity and anisotropy ?

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

radial - SR direction

transverse - perpendicular to radial

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List 2 processes commonly applied when processing VSP data

deconvolution
stack
mute
filter/scale

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describe 2 differences seen between P wave and S wave section

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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State 2 properties of P and S waves

P waves travel 2x faster than S waves

No S waves in liquids

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What is surface consistent process

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

cross correlation

comparison of 2 different wavelets | in vibroseis produces zero phase wavelet by way of linear filter

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

velocity sag | pull-up

what 2 false structures do the velocity affects create ?

velocity sag produces false syncline | pull up produces false rollover

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

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

List structural and stratigraphic features visible on coherence cube images ?

structural features -- faults | stratigraphical features - reefs, river channels and deltas

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

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

what does impedance represent ?

acoustic impedence -- properties of the layer

what does seismic amplitude represent ?

attribute of the layer boundaries

list 4 surface consistent processes in the processing sequence

3D amplitude compensation spiking deconvolution refraction statics reflection statics

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

``` Migration Domain (Time or Depth Domain) Methods (1 pass or 2 pass) ```

what is depth step ?

in time or depth | increment in which migration process is applied

what is migration aperture?

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

what are migration velocities

stacking velocities slowed by 5-10%

List difference between Post stack and Pre Stack Migration

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

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

trace amplitudes are migrated to proper bin prior to stacking

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

Vint Post Stack 3D migration results well data VSP

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

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

What's the purpose of a match filter ?

match 2 data sets (shape and frequency)

What are the 3 properties of a multiple?

slower velocity | polarity reversal

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

RC changes and becomes a negative value

State a purpose of VSP

in-situ rock properties in depth

List 5 types of VSP

``` walkaway VSP multi-azimuth VSP zero offset VSP 3D vsp cross-well VSP ```

define inhomogenous

measure property inconsistent in XY direction

define isotropic

sdfs

define azimuthal anisotropy

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

define S wave

shear wave | particle motion is perpendicular to propagation of wave

list linear shot noise

ground roll air waves backscatter

What's the effect of summing or stacking data

increase coherent signal and reduce incoherence signal

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

offset | azimuth

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

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

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

enhance reservoir characterization

State 2 possible OBC acquisition geometries

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

what are free surface multiples ?

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

What's the purpose of VSP ?

match VSP with surface seismic to identify multiples

Name some properties of multiples

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

what's SUPERGATHER

CDP gather w summation of adjacent CDP gather