minimises subsurface
mapping risk away from
hard data locations (wells)
acoustic imaging of the
subsurface in 2way time
Acoustic pulse is partially transmitted+
reflected at boundaries betw. rocks
with different acoustic impedence
complicated extension of
echo (water depth) sounder
source emit sound down through earth- interfaces
where impedance changes partially reflect sound
up-record- reflection strength determined by
difference acoustic impedence (Z) across interface.
reflection coefficient determine
amplitude of reflected wave
move device in a line produce 2D mapping, in a grid
produce 3D mapping. difficult to move device-3D is
provide by many closely-space receivers in grid.
Depth resolution
poor relative to log+other well data
(spatial/geographic resolution). typical
range: quarter to half wavelenth
size of smallest distinguishable
features in the data
Steps
1. Acquisition
survey is designed+shot
compositions
source of sound
air guns (marine)
vibroseis truck (land)
frequency range: 8-80Hz
receiver detect returning echo
geophones (land)
hydrophones (marine)
amplify, digitise, record data instruments
Cheaper in sea (equipment loaded on
boat, operate day+night) than land
(manual load equipments, electric cables)
2. Processing
intensive computer
processing-image
from seismic data
data pass through
separate processes,
different purposes
Random noise suppression
improve signal:sound
Common Midpoint Shooting (CMP)
data shot so many
reflections record from same
point-reflections add
together- make stack
section- better signal-noise
ratio than original data
CMP gathers: raw, recorded
shot records. not easy integret
combine CMPs -transform to
geologically meaningful
display that can be integret
Velocity Analysis for correcting Normal Moveout (NMO)