misc test ques Flashcards
true or false
p wave velocity is approx 2x S wave velocity
TRUE
true or false
4D surveys are useful for monitoring reservoir production over a time period
TRUE
true or false
wide azimuth surveys are characterized by a large variation in shot and receiver azimuths over narrow azimuth surveys
TRUE
true or false
shear vibrators are used to generate sheer waves for 3C land surveys
TRUE
true or false
each component of a multi-component data set is recorded on a separate seismic channel
TRUE
What’s the acronym mean ?
CCP
Common Conversion Point
What’s the acronym mean ?
CMP
Common Mid Point
What’s the acronym mean?
VSP
Vertical Seismic Profile
What does the acronym mean ?
PSv
Pwave to vertical Swave conversion
What’s the acronym mean?
CDP
Common Depth Point
Define 3C /4D
2 or 3 surveys done over time
Define azimuthal anisotropy
regional stress orientation
rocks fractured EW travels faster than NS
Define P/Z data
vertical component of particle velocity recorded from geophone is scaled and summed with pressure from receiver side water layer reverberations
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
What are the 2 possible OBC acquisition geometries?
orthogonal
parallel
In MC acquisition, what are the 3 methods of cable deployment?
dragged cable
draped cable
dragged and draped
explain 2C acquisition
2 component
hydrophone P wave
geophone vertical
Marine
explain 4C acquisition
4 components
1 hydrophone P wave
3 geophones – 2 horizontal and 1 vertical
3 basic steps of C-wave data processing
Preprocessing of all components
P wave time and depth processing
C wave time and depth processing
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.
The horizontal component energy is transferred between 2 components - which are they ?
radial - SR direction
transverse - perpendicular to radial
List 2 processes commonly applied when processing VSP data
deconvolution
stack
mute
filter/scale
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
State 2 properties of P and S waves
P waves travel 2x faster than S waves
No S waves in liquids
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
