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geo 395 > geo 395- case studies mod 8,10 > Flashcards

geo 395- case studies mod 8,10 Flashcards

0
Q

first arrival

A

muted after NMO correction or deconvolution

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1
Q

Reasons for amplitude correction

A
  • lateral reflector amplitude variations
  • spherical divergence
  • absorption
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2
Q

reasons for statics in land and marine

A

land : elevation and velocity variations weathering layer -thickness variations

marine data: source array and depth correction delay due to variations in water depth

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3
Q

consequences of uncorrected static shift

A

traces are unaligned even after NMO correction appearance of false structure

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4
Q

T D

A

time correction of datum

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5
Q

E D

A

elevation of datum

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6
Q

E S

A

source elevation

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7
Q

D S

A

depth of shot

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8
Q

E G

A

elevation of geophone

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9
Q

D SG

A

depth of shot near geophone

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10
Q

T UGH

A

uphole time at geophone location

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11
Q

V W

A

weathering velocity

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12
Q

V
B

A

velocity of bedrock

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13
Q

Residual statics

A

static correction with CDP gathers and reflection gathers used for rapid variation in near surface refraction statics and NMO

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14
Q

residual statics- method

A

use cross correlation for static shift of each trace in CDP gather

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15
Q

shot static

A

static value applied to all traces of a given shot

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16
Q

receiver static

A

static value applied to an individual (0, -1,1)

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17
Q

gather types

A

shot gather common depth pt gather common receiver gather

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18
Q

shot gather

A

shot and all its traces

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19
Q

common depth point gather

A

gather and all traces with common reflection pt

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20
Q

common receiver gather

A

gather of all traces recorded by 1 geophone group

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21
Q

filter

A

conversiono f an input signmal into an output signmal in such a way that you know the answer

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22
Q

cross correlation

A

comparison of different traces or wavelets used in residual statics

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23
Q

auto correlation

A

comparion of identical traces or wavelets output wavelets are either zero phase or symmetrical used in deconvolution

24
Q

deconvolution

A

attempts to derive original reflection coeeficient series Rc * w(t) = s(t)

25
Q

Dereverberation

A

removal of multiples

26
Q

Kinds of multiples

A
  1. water-bottom multiples
  2. intra-bed multiples
  3. inter-bed multiples
  4. peg-leg multiples
  5. free surface multipes
27
Q

water bottom multiples

A
28
Q

intra-bed multiples

A

goes through 2-3 layers

29
Q

inter-bed multiples

A

think W

30
Q

peg-leg multiples

A

think pirate

31
Q

free surface

A
32
Q
A
33
Q

Amplitude spectra

A
34
Q

phase spectra

A

3 values for 3 component traces

35
Q

CVG

A

CONSTANT VELOCITY GATHER

single CDP gather is NMO Corrected with a single velocity time pair

36
Q

CVS

A

CONSTANT VELOCITY SOURCE

adjacent CDP gather and NMO corrected with a single velocity function derived from CVG

37
Q

outcomes of NMP correction

A

3 options

correct velocity

velocity is too slow (overcorrection)

velocity is too fast (undercorrection)

38
Q

NMO Equation

A

0

T2 = T02 + X2 / V2

T - non zero offset arrival time

T0 zero offset arrival time

V velocity

X offset

39
Q

Seismic Data Display Types

A

wiggle trace

variable area

variable and wiggle trace

variable dencity

40
Q

Display parameters

A

Horizontal Scale (Traces per inch or Traces per cm)

Vertical scale (Inches per sec or cm per sec)

Polarity (normal or reverse)

41
Q

migration

A

process that repositions to its correct subsurface positions

42
Q

Migration algorith

A

Kirchoff

Finite Difference

Bowtie —– migration —> syncline

43
Q

SONIC LOG

A

sound generator + 4 receivers

interval velocities are calculated from travel times

used to identify P and S waves

44
Q

DENSITY LOG

A

measures gamma ray backscatter from a rock formation

Backscatter is proportional to electron density of rock which is proportional to bulk density

Natural radioactivity has no effect on density logs

45
Q

GAMMA RAY LOG

A

Measure of natural radioactivity

used to identify shales

46
Q

Caliper Log

A

measurement of borehold diameter

gives info on lithology, porosity and permeability

47
Q

Well Velocity Survey

A

identifies relations between surface geology and seismic reflection data

48
Q

VSP

A

Vertical Seismic Profile

Downward events (primary and multiples)

increase with time and depth

Upward events (primary and multiples)

decrease with time and depth.

49
Q

Recipe for constructing synthetic seismogram

A
  1. Use sonic and density log to create acoustic impedence AI = p x v
  2. Create reflection coefficient from AI log Rc=(P2V2 -P1V1 / P2V2+P1V1)
  3. Convolve RC series with a source wavelet thus creating 1 synthetic trace Rc * w(t) = s(t)
  4. copy synthetic trate 5-6 times
  5. create reverse polarity set from the set of synthetic traces due to field acquisition poliarities being opposite
  6. apply 3-6 bandpass filters to the normal revers synthetic traces
50
Q

Acquisition reasons for mistie

A

source type

field filters

sample rate

field polarity

vintage

51
Q

processing reasons for mistie

A

NMO

statitcs

deconvolution

migration

velocities

vintage

52
Q

What should correlations be ?

A

interval best fit

53
Q
A
54
Q

time variant

A

filter change down seismic section

55
Q

time invariant

A

one filter for the whole section

eg stretching and squeezing

56
Q

cross correlation

A

comparison of 2 unequal traces

Cross correlation gives static shift necessary to align data of 2 seismic traces

57
Q

auto-correlation

A

comparison of 2 equal traces

output is a zero phase wavelet

good for identifying short multiples

58
Q

match filter

A

takes 2 data sets and matches frequency, phase and amplitude.

It’s a way to merge vibe and dynamite data

geo 395 (11 decks)

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