Title: SEISMIC
1SEISMIC DATA GATHERING
2GEOPHONE STRUCTURE
3GEOPHONE TYPES FREQUENCY
4SOURCE TRUCKS
53D-SEISMIC COVERAGE
6CDP FOLD STACK
7MARINE SEISMIC CABLE LAYOUT
8MULTIPLE RAYPATH
9ATTENUATION TECHNIQES
10SEISMIC DATA PROCESSING
11PROCESSING FLOWCHART
12OBJECTIVE OF PROCESSING
13EFFECT OF STACKING ON NOISE
SIGNAL PLUS RANDOM AT SIX-DETECTOR ARRAY
NOISE
SIGNAL
SIGNAL NOISE
SIGNAL NOISE EACH RECEIVER
SUMMED OUTPUT
14POST-STACK PROCESSING
- RESIDUAL STATICS
- DISPLAY ENHANCEMENT
- MIGRATION
- ATTRIBUTE ANALYSIS
- INVERSION
- TIME-DEPTH CONVERSION
15SUMMARY OF SEISMIC PROCESSING
- DATA ARE GATHERED AND CMP-ORDERED GATHERS ARE
FORMED
- VELOCITY ANALYSIS IS PERFORMED ON SELECTED GATHERS
- THE GATHERS ARE MOVEOUT CORRECTED, STACKED, AND
PLOTTED
- STACKING MAY BE FOLLOWED BY ADDITIONAL PROCESSING
16FACTORS AFFECTING AMPLITUDE
17VELOCITY ANALYSIS
NORMAL MOVEOUT (NMO)
X
TX - T0
TX
T0
IMAGE POINT
WHERE T0 ZERO OFFSET TIME
18NMO-ISOTROPIC LAYER
X
A
C
Z
B
D
IMAGE POINT
19MULTI-LAYER CASE
20HOW IS VNMO DETERMINED?
FOR EACH TRACE T AND X VALUES ARE DETERMINED
21VELOCITY ANALYSIS
HYPERPOLA PLOTS AS A STRAIGHT LINE ON T2 - X2
GRAPH
22VMNO CORRECTION
KNOWING THE VNMO, T? AND OFFSET, THE TIME
CORRECTION NECESSARY TO SHIFT EACH TRACE CAN BE
CALCULATED
23INTERVAL VELOCITY DETERMINATION FROM SEISMIC
FROM VELOCITY ANALYSIS, WE KNOW
VNMO1,T0,1 VNMO2, T0,2 SUBTITUTING THESE
VALUES INTO THE DIX EQUATION
24MIGRATION EFFECTS
- FLAT HORIZONS REMAIN UNCHANGED IF THERE ARE NO
VELOCITY ANOMALIES ABOVE - DIPPING HORIZONS BECOME STEEPER, SHALOWER, AND
MOVE LATERALLY UPDIP - SYNCLINES BECOME BROADER, WITH ANY BOW TIES
ELIMINATED - ANTICLINES BECOME NARRWER
- DIFRACTIONS COLLPSE TO POINTS
25 RAY PATH MIGRATION
WHERE ? TRUE DIP OF REFLECTOR ? APPERENT
DIP OF REFLECTOR V VELOCITY
26WHY MIGRATE?
IF BEDS ARE DIPPING, APPERENT POSITION OF EVENTS
ON A STACKED SECTION DIFFERS FROM THEIR TRUE
POSITION
DEPTH MODEL
ARRIVAL TIMES
7 KFT/SEC
TIME
DEPTH
9 KFT/SEC
11 KFT/SEC
27ASSUMPTION UNDERLYING MIGRATION
- ALL EVENTS ARE PRIMARIES-
- NO NOISE, NO MULTIPLES, NO SHEAR WAVES
- ALL EVENTS COME FROM THE PLANE VERTICALLY
- BENEATH THE SEISMIC LINE-
- NO SIDEWIPE
- VELOCITY ARE KNOWN EVERY WHERE
28MIGRATION MOVES DIPPING HORIZONS
29FOCUSING EFFECT OF A SHARP SYNCLINE
30DEFOCUSING EFFECT OF AN ANTICLINE
31FOCUSING EFFECT OF A SYNCLINE
32 3-D MIGRATION
- ELIMINATES ASSUMPTION OF 2--D MIGRATION THAT ALL
DATA COMES FROM WITHIN PLANE OF SECTION - REQUIRES 3-D DATA COLLECTION TO INSURE CLOSELY
SPACED TRACES IN BOTH X, Y DIRECTIONS - MOVES ENERGY IN BOTH INLINE AND CROSSLINE
DIRECTIONS - INLINES AND CROSSLINES TIE AFTER 3-D MIGRATION
- MAP MIGRATION IS AN ALTERNAIVE FOR COARSE GRID
OF 2-D LINES
33 TIME VS. DEPTH SECTIONS