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EXPLORATION GEOPHYSICS. EARTH MODEL NORMAL-INCIDENCE REFLECTION AND TRANSMISSION COEFFICIENTS WHERE:  1 = DENSITY OF LAYER 1 V 1 = VELOCITY OF LAYER.

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Presentation on theme: "EXPLORATION GEOPHYSICS. EARTH MODEL NORMAL-INCIDENCE REFLECTION AND TRANSMISSION COEFFICIENTS WHERE:  1 = DENSITY OF LAYER 1 V 1 = VELOCITY OF LAYER."— Presentation transcript:

1 EXPLORATION GEOPHYSICS

2 EARTH MODEL

3 NORMAL-INCIDENCE REFLECTION AND TRANSMISSION COEFFICIENTS WHERE:  1 = DENSITY OF LAYER 1 V 1 = VELOCITY OF LAYER 1  2 = DENSITY OF LAYER 2 V 2 = VELOCITY OF LAYER 2 DENSITY  1 VELOCITY V 1 DENSITY  2 VELOCITY V 2 REFLECTION COEFFICIENT TRANSMISSION COEFFICIENT

4 SEISMIC ACQUISITION

5 GEOPHONE STRUCTURE

6 GEOPHONE TYPES & FREQUENCY

7 SOURCE TRUCKS

8 3D-SEISMIC COVERAGE

9 CDP & FOLD STACK

10 MARINE SEISMIC CABLE LAYOUT

11 MULTIPLE RAYPATH

12 FACTORS AFFECTING AMPLITUDE

13 ATTENUATION TECHNIQES

14 SEISMIC DATA PROCESSING

15 PROCESSING FLOWCHART

16 OBJECTIVE OF PROCESSING REAL EARTH EARTH PROPERTIES PULSE SEISMIC TRACE PROCESSING MODEL EARTH

17 EFFECT OF STACKING ON NOISE SIGNAL PLUS RANDOM AT SIX-DETECTOR ARRAY SIGNAL SIGNAL + NOISE NOISE SIGNAL + NOISE EACH RECEIVER SUMMED OUTPUT

18 SEISMIC-WELL TIES PURPOSE: TO COMBINE TWO DATA SETS FOR A MORE COMPLETE INTERPERATION SEISMIC DATA TWO WAY TIME SEISMIC VELOCITY SEISMIC IMPEDENCE SEISMIC SEQUENCES SEISMIC FACIES STRUCTURE WELL DATA LINEAR DEPTH VELOCITY DENSITY GEOLOGIC AGE LITHOLOGY FAULT ORIENTATION

19 ACOUSTIC STRUCTURE OF EARTH LAYERED EARTH SONICDENSITYRC

20 CONVOLUTION

21 DETAILED SYNTHETIC SEISMOGRAM

22

23 POST-STACK PROCESSING RESIDUAL STATICS DISPLAY ENHANCEMENT MIGRATION ATTRIBUTE ANALYSIS INVERSION TIME-DEPTH CONVERSION

24 SUMMARY 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

25 VELOCITY ANALYSIS NORMAL MOVEOUT (NMO) X TXTX = T X - T 0 IMAGE POINT WHERE T 0 = ZERO OFFSET TIME T0T0 T0T0

26 NMO-ISOTROPIC LAYER A X C Z IMAGE POINT B D WHERE THEREFORE

27 MULTI-LAYER CASE FOR LAYER 1: FOR LAYER 2: V NMO = NORMAL MOVEMEOUT VELOCITY ASSUMED RAYPATH FOR V NMO CALCULATION X T X,1 Z V1V1 T 0,1 T 0,2 T X,2 ACTUAL RAYPATH

28 HOW IS VNMO DETERMINED? FOR EACH TRACE T AND X VALUES ARE DETERMINED

29 VELOCITY ANALYSIS HYPERPOLA PLOTS AS A STRAIGHT LINE ON T 2 - X 2 GRAPH T 2 - X 2 PLOT X2X2 OFFSET 2 t2t2 Y=b+mX WHERE

30 VMNO CORRECTION KNOWING THE VNMO, T  AND OFFSET, THE TIME CORRECTION NECESSARY TO SHIFT EACH TRACE CAN BE CALCULATED

31 INTERVAL VELOCITY DETERMINATION FROM SEISMIC FROM VELOCITY ANALYSIS, WE KNOW VNMO 1,T 0,1 VNMO 2, T 0,2 SUBTITUTING THESE VALUES INTO THE DIX EQUATION

32 MIGRATION 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

33 RAY PATH MIGRATION WHERE  = TRUE DIP OF REFLECTOR  = APPERENT DIP OF REFLECTOR V= VELOCITY REFLECTION REFLECTOR x t

34 WHY MIGRATE? IF BEDS ARE DIPPING, APPERENT POSITION OF EVENTS ON A STACKED SECTION DIFFERS FROM THEIR TRUE POSITION DEPTH MODEL DEPTH TIME ARRIVAL TIMES 7 KFT/SEC 11 KFT/SEC 9 KFT/SEC

35 ASSUMPTION 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

36 MIGRATION MOVES DIPPING HORIZONS

37 FOCUSING EFFECT OF A SHARP SYNCLINE

38 DEFOCUSING EFFECT OF AN ANTICLINE

39 FOCUSING EFFECT OF A SYNCLINE

40 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

41 TIME VS. DEPTH SECTIONS

42 CDP GATHER AFTER DEMULTIPLEXING

43 CDP GATHER AFTER AMPLITUDE CORRECTION

44 CDP GATHER AFTER DECONVOLUTION

45 VELOCITY ANALYSIS

46 CDP GATHER AFTER NMO CORRECTION

47 CDP GATHER AFTER MUTING STRETCHED ZONES

48 CDP STACKED SECTION

49 CDP STACKED SECTION WITH TVF FILTER


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