SUB SURFACE FEATURES OF INTEREST IN HYDROCARBON EXPLORATION ARE
THREE DIMENSIONAL IN NATURE. IN ORDER TO HAVE ADEQUATE AND DETAILED
IMAGE OF THE SUBSURFACE, IT IS ESSENTIAL TO USE 3-D IMAGING
TECHNIQUE.
ADVANTAGES OF 3D
IMAGING OF SUB SURFACE
RESERVOIR GEOPHYSICS
IMAGING OF SUB SURFACE
DELINEATION OF 3D SUBSURFACE FEATURES USING 2D SURVEYS OFTEN LEADS
TO AMBIGUITY.THE SUBSURFACE GENERALLY DIPS IN MANY DIRECTIONS IN
AREAS WHERE STRUCTURAL TRAPS ARE BEING EXPLORED.
RESERVOIR GEOPHYSICS
PHYSICAL PARAMETERS NEEDED TO PROPERLY DEVELOP HYDROCARBON
RESERVOIRS SUBSTANTIALLY EXCEEDS THE DETAIL REQUIRED TO FIND THEM.
DUE TO THIS THERE IS A STEADY INCREASE IN APPLICATION OF 3D SEISMIC
TO RESERVOIR MANAMGEMENT.
RESERVOIR GEOPHYSICS
3D SEISMIC IMPACTS RESERVOIR MANAGEMENT IN TWO WAYSIDENTIFICATION
OF RESERVES REMAINED UNRECOVERD BY EXISTING DEVELOPMENT PLAN.SAVE
COSTS BY MINIMISING DRY HOLES AND POOR PRODUCERS.
RESERVOIR GEOPHYSICS
THE 3D SEISMIC CAN PROVIDE QUANTITATIVE ESTIMATES OF THE ROCK
PROPERTIES WHICH ARE USED AS INPUT INTO RESERVOIR SIMULATION
MODELS.
SEISMIC CABLESGEOPHONESRECORDING INSTRUMENTMAGNETIC TAPESSHOOTING
SYSTEMSCOMMUNICATION SETSSHOT HOLE DRILLING ENERGY
SOURCESTRANSPORTATION
ENERGY SOURCES
DYNAMITE (LAND)VIBROSEIS (LAND)AIRGUN (OFFSHORE)
SHOT HOLE DRILLING
MANUAL DRILLING JET BORINGTRUCK MOUNTED RIGS
PRE PLANNING
PROGRAMME RECONNAISSANCEPROJECT REPORTPROCUREMENT / COLLECTION OF
REQUIRED EQUIPMENT
DATABASE
GEOLOGICAL/INTERPRETATIONAL OBJECTIVESGRAVITY ANAMOLY MAPSTOPO
SHEETS OF THE AREAPREVIOUS SEISMIC WORK DONE RELEVANT SEISMIC
SECTION TIME STRUCTURE MAPSWELL DATA / VSP DATA
EXPERIMENTAL WORK
UP HOLE SURVEYSHALLOW REFRACTION SURVEYNOISE ANALYSISFOLD BACK
EXPERIMENT
FORMULA FOR MULTIPLICITY
MULTIPLICITY =( N*S)/(2*n)N= no. of channels in the spreadS = no.
of shot points for the spreadn = no. of stations by which the
spread is advanced
EXAMPLE
MULTIPLICITY =( N*S)/(2*n)If N = 48, S = 1, n =1, then M = 24If N =
48, S = 1, n =2, then M = 12If N = 96, S = 1, n =1, then M = 48If N
= 96, S = 1, n =2, then M = 24
OFFSET DISTRIBUTION
IDEALLY , IT IS DESIRABLE TO HAVE A WIDE SELECTION OF OFFSETS
FOR EACH COMMON- CELL GATHER. OTHERWISE SMALL ERRORS IN MOVE OUT
CORRECTION MAY CAUSE TRACE TO TRACE CHALTER ON STACKED ON
SECTIONS.
EVEN OFF SET DISTRIBUTION
NEAR 12 NEAR MIDDLE 12FAR MIDDLE 12FAR 12
3D GEOMETRIES
SWATH PATTERNBRICK PATTERNSEIS LOOPSEIS SQARE
#1
#60
SWATH 3D GEOMETRY
#61
#120
#121
#180
#181
#240
R1
R2
R3
R4
S4
4 R/L - R1, R2, R3, R4 & S/L - S4
G.I = 50M, SP.I = 100M, BIN SIZE = 25M X 50M
R/L INT.=100M, S/L INT.=100M, NEAR OFFSET = 300 & 350M
#1
#60
BRICK PATTERN 3D GEOMETRY
#61
#120
#121
#180
#181
#240
R1
R3
R5
R7
S5
S6
S7
S8
4 R/L - R1, R3, R5, R7 & 4 S/L - S5, S6, S7, S8
G.I = 50M, SP.I = 100M, BIN SIZE = 25M X 50M
R/L INT.=200M, S/L INT.=100M, NEAR OFFSET = 300 & 350M
SHOOTING DIRECTION
STRIKE LINE SHOOTING45 DEGREE FROM DIP DIRECTIONDIP LINE
SHOOTING
MARINE ACQUISITION
THE MOST COMMON MARINE 3D DATA ACQUISITION INVOLVES SHOOTING A
NUMBER OF CLOSELY SPACED PARALLEL 2D LINES
BIN
A BIN IS A SMALL SUB SURFACE AREA WHICH DEFINES ONE SET OF
RECORDED TRACES TO BE STACKED TOGETHER IN PROCESSING.
BIN SIZE = G.I X S.I
MIGRATION
MIGRATION IS THE PROCESS OF MAKING THE REFLECTION SURFACE
COINCIDE WITH THE GEOLOGICAL SURFACE BY MOVING OR MIGRATING EACH
REFLECTION POINT TO ITS PROPER POSITION IN THE SUB SURFACE.
MIGRATION APERTURE
THE NUMBER OF TRACES TO BE INCLUDED IN THE STACK.
THE SIZE OF THE APERTURE DEPENDS ON DIP, REFLECTION TIME OF THE
EVENTS ON THE UNMIGRATED SECTION AND VELOCITY.
MIGRATION APERTURE NEED NOT BE SAME IN ALL DIRECTIONS AS IT
DEPENDS UPON THE STEEPNESS OF DIPS AT THAT END.
FRESNEL ZONE
THE CHANNEL SPACING HAS BEARING ON A LATERAL RESOLUTION. REFLECTED
ENERGY REPRESENTS SAMPLING NOT FROM A SINGLE POINT, BUT FROM AN
AREA ON THE REFLECTING SURFACE. THIS AREA IS CALLED FIRST FRESNEL
ZONE. ITS RADIUS R IS GIVEN BY,R= D/2 WHERE D IS DEPTH OF
REFLECTING SURFACE AND IS WAVE LENGTH OF REFLECTED ENERGY.
