SEISMIC DATA GATHERING

GEOPHONE STRUCTURE

GEOPHONE TYPES & FREQUENCY

SOURCE TRUCKS

3D-SEISMIC COVERAGE

CDP & FOLD STACK

MARINE SEISMIC CABLE LAYOUT

MULTIPLE RAYPATH

ATTENUATION TECHNIQES

SEISMIC DATA PROCESSING

PROCESSING FLOWCHART

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

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

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

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

FACTORS AFFECTING AMPLITUDE

VELOCITY ANALYSIS NORMAL MOVEOUT (NMO) X = TX - T0 TX T0 IMAGE POINT WHERE T0 = ZERO OFFSET TIME

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

ASSUMED RAYPATH FOR VNMO CALCULATION MULTI-LAYER CASE ASSUMED RAYPATH FOR VNMO CALCULATION X TX,1 Z V1 T0,1 T0,2 TX,2 ACTUAL RAYPATH FOR LAYER 1: FOR LAYER 2: VNMO = NORMAL MOVEMEOUT VELOCITY

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

VELOCITY ANALYSIS Y=b+mX T2 - X2 PLOT X2 OFFSET2 t2 HYPERPOLA PLOTS AS A STRAIGHT LINE ON T2 - X2 GRAPH Y=b+mX WHERE

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

INTERVAL VELOCITY DETERMINATION FROM SEISMIC FROM VELOCITY ANALYSIS, WE KNOW VNMO1,T0,1 VNMO2, T0,2 SUBTITUTING THESE VALUES INTO THE DIX EQUATION

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

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

WHY MIGRATE? TIME DEPTH DEPTH MODEL ARRIVAL TIMES 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

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

MIGRATION MOVES DIPPING HORIZONS

FOCUSING EFFECT OF A SHARP SYNCLINE

DEFOCUSING EFFECT OF AN ANTICLINE

FOCUSING EFFECT OF A SYNCLINE

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

TIME VS. DEPTH SECTIONS