Seismic Reflection Method

How Karcher "hand migrated" dipping layer

Top: Monument unveiled in 1971 at Belle Isle (Oklahoma City) on 50th anniversary of first seismic reflection survey by J. C. Karcher. Middle: Two early reflection records from Belle Isle, 1921. Bottom: Karcher's interpretation of same.

Polarity of reflected wave depends on sign of reflection coefficient (unchanged polarity means compression remains compression, dilatation remains dilatation)

Hypothetical Rock Properties
Rock VP, km/s ρ, kg/m3 V x ρ
Granite 5.0 2700 13,500
Basalt 5.5 3000 16,500
Limestone 6.0 2300 13,800
Sandstone 4.2 2500 10,500
Shale 2.5 2300 5,750

For these hypothetical values, limestone-granite contact will be poor reflector

Simple Zero-offset Reflection Survey

Seismic Reflection Survey with Offset, Single-fold Coverage

Note that subsurface reflection points have half the spacing of geophones. To get complete "single-fold "coverage of the subsurface, can shoot from either end of geophone spread:

One can also use a "split-spread" arrangement, here with shot at point B, then move half the geophones forward and shoot at C:

The next two figures show recording-truck signal check for 36-channel split-spread layout:

 

The travel time for the primary reflection (first layer) where geophone offset = x, thickness d, velocity V


this is a hyperbola:

Multiple Layers

Green Method

The Dix Equation

Velocity Scans - another way to get stacking velocity:

Signal Summing; Stacking

geophone groups

"Geophones are rarely used singly. Normally several (as many as 20 or more) are electrically connected to each other in a group in such a way that the outputs of the individual phones are effectively summed. The information from each group must be transmitted via cables to the recording truck. In modern land recording with 48, 96, or more group recordings, the cables are long and heavy and often add noise to the recording, especially in the presence of powerlines or water." - Dobrin and Savit, Introduction to Geophysical Prospecting, 4th ed.

multiple shots

multi-fold coverage

Rock Velocities

Data Collection

Source

Geophones

Recording Digitally

Processing Steps

AGC: automatic gain control

Filtering

Statics Removal

vertical velocity distribution near the surface determined by shooting up the hole" (Geophysical Services, Inc.):

Migration

Synthetic Seismograms

Directions Seismic Reflection is Heading

Percentage of seismic activity involving various techniques. (Data from SEG annual Geophysical Activity Reports, pre-1981 data are for U.S. activity, post-1980 for worldwide activity, 3-D data from Dutt, 1992, adjusted according to judgment expressed in Goodfellow, 1991.)

Seismic Attributes

Conventional B&W section on which carbonate bank would be missed:

Color display in which colors are keyed to interval velocity estimates (1000 ft/s increments):

Close-up of carbonate bank sequence seen above:

3-D Seismic Reflection

3-D sesimic time slices at time ranging from 1060 ms to 1260 ms:

Summary of Processing Steps