1
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2
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- The only method giving complete picture of the whole area
- Gives by far the best resolution among other geophysical methods
(gravity and magnetic)
- However, the resolution is still limited
- Maps rock properties related to porosity and permeability, and presence
of gas and fluids
- However, the links may still be non-unique
- Requires significant logistical effort
- Relies on extensive data processing and inversion
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3
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4
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5
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6
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7
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- Start with regional 2-D reconnaissance lines
- Following the initial discovery – detailed 2-D or 3-D
- Repeated 3-D surveys (“time-lapse”, or 4-D) for monitoring changes in
the area during production
- For best survey planning:
- In most cases, need to have a good idea about the target
- Use computerized pre-acquisition modelling
- Key considerations:
- For 2-D – lines should be oriented across-strike of the target
structures
- Cost – minimize the number of source points
- Achieve sufficient multiplicity (“fold”) of coverage
- Achieve uniformity of coverage of the target horizons
- “Undershoot” obstacles and survey edges
- Achieve adequate resolution and fidelity
- Reduce the acquisition footprint (especially important in 3-D)
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8
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9
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- Gelatin dynamite, ammonium nitrate, pentolite (SEIS-X).
- Packaged in tins, cardboard or plastic tubes ~5 cm in diameter (0.5-5 kg
each).
- Connected to make desired charges.
- Detonated using electrical detonators.
- Best explosives will disintegrate from contact with water when not used.
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10
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11
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12
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- Rather than using explosions, acoustic energy can be distributed in time
by using a hydraulic vibrator device
- Usually mounted on a heavy truck
- Small borehole vibrators, portable vibrators, and >100-ton
stationary vibrators also exist.
- The signal consists of a quasi-monochromatic “sweep” of gradually
changing frequency, covering ~20-150 Hz
- To produce stronger signal, vibrators are able to operate synchronously
(vibrate in-phase) in a group
- The signal sent into the ground is carefully recorded and afterwards
“correlated” with the recordings to produce an equivalent of impulsive
excitation
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13
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14
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15
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16
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17
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18
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19
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20
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21
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22
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23
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24
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25
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26
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27
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28
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29
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