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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
deconvolution
attempts to derive original reflection coeeficient series Rc \* w(t) = s(t)
25
Dereverberation
removal of multiples
26
Kinds of multiples
1. water-bottom multiples 2. intra-bed multiples 3. inter-bed multiples 4. peg-leg multiples 5. free surface multipes
27
water bottom multiples
28
intra-bed multiples
goes through 2-3 layers
29
inter-bed multiples
think W
30
peg-leg multiples
think pirate
31
free surface
32
33
Amplitude spectra
34
phase spectra
3 values for 3 component traces
35
CVG
CONSTANT VELOCITY GATHER single CDP gather is NMO Corrected with a single velocity time pair
36
CVS
CONSTANT VELOCITY SOURCE adjacent CDP gather and NMO corrected with a single velocity function derived from CVG
37
outcomes of NMP correction
3 options correct velocity velocity is too slow (overcorrection) velocity is too fast (undercorrection)
38
NMO Equation
0 T2 = T02 + X2 / V2 T - non zero offset arrival time T0 zero offset arrival time V velocity X offset
39
Seismic Data Display Types
wiggle trace variable area variable and wiggle trace variable dencity
40
Display parameters
Horizontal Scale (Traces per inch or Traces per cm) Vertical scale (Inches per sec or cm per sec) Polarity (normal or reverse)
41
migration
process that repositions to its correct subsurface positions
42
Migration algorith
Kirchoff Finite Difference Bowtie ----- migration ---\> syncline
43
SONIC LOG
sound generator + 4 receivers interval velocities are calculated from travel times used to identify P and S waves
44
DENSITY LOG
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
GAMMA RAY LOG
Measure of natural radioactivity used to identify shales
46
Caliper Log
measurement of borehold diameter gives info on lithology, porosity and permeability
47
Well Velocity Survey
identifies relations between surface geology and seismic reflection data
48
VSP
Vertical Seismic Profile Downward events (primary and multiples) increase with time and depth Upward events (primary and multiples) decrease with time and depth.
49
Recipe for constructing synthetic seismogram
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
Acquisition reasons for mistie
source type field filters sample rate field polarity vintage
51
processing reasons for mistie
NMO statitcs deconvolution migration velocities vintage
52
What should correlations be ?
interval best fit
53
54
time variant
filter change down seismic section
55
time invariant
one filter for the whole section eg stretching and squeezing
56
cross correlation
comparison of 2 unequal traces Cross correlation gives static shift necessary to align data of 2 seismic traces
57
auto-correlation
comparison of 2 equal traces output is a zero phase wavelet good for identifying short multiples
58
match filter
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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