Source and Receiver have always the same distance Moveout must be taken into account or corrected for Common-Offset... Source and receiver are at the same location i.e.. the offset is ze
Trang 1• Common-offset & Zero-offset
• Common-midpoint method
• Up-dip and down-dip shooting
• Spread types
• Singlefold / Multifold recording
• Crooked line method
• Determining field parameters
Trang 2Source and Receiver have always the same distance
Moveout must be taken into account or corrected for
Common-Offset
Trang 3Source and receiver are at the same location (i.e the offset is zero -> “zero offset”)
=> No Move-out
Zero-Offset
Trang 4CMP = CDP
CMP ¹ CDP
CMP = common mid point CDP = common depth point
CMP - “ Common Mid Point”
Trang 5+
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Down-dip shooting
Up-dip shooting
Remember the refraction measurement where both shooting
directions were needed to estimate the velocity of the lower layer
Trang 6(Top view)
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single ended (end on)
split spread fan shooting
single ended (inline offset)
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Common field layouts
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active not-active
active
active
more Geophones in the Field than active channels
Geometry of Geophones relative to the source remains the same
roll along
Trang 8“roll along acquisition”
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active not-active
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Trang 9Sources and receivers on a road Resulting line
From Sheriff, 1995
Trang 10From Reynolds, 1997
Trang 11Xo=(Xs-Xr)/2 Xm=(Xs+Xr)/2
From Reynolds, 1997
Trang 12●
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distance geoph: 1, distance source: 2,
No geophones: 4, distance geoph: 1, distance source: 1, Fold: 2
Fold: 1
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Trang 14Number of traces per CMP
shots e
between th Distance
* 2
geophones e
between th Distance
* geophones of
Number
Fold =
Coverage (“fold”)
% 100
* Fold Coverage =
Trang 15From Reynolds, 1997
Trang 16• Maximum offset » Depth deepest zone of interest
• Minimum offset » Not greater than shallowest section of interest
• Maximum array length is determined by the
minimum apparent velocity of reflections
• Charge size determined by ambient noise late on the record
• Line orientation (up-dip, down-dip)