Processing sequence for statics corrections

Seismic Data Analysis

Series	Investigations in Geophysics
Author	Öz Yilmaz
DOI	http://dx.doi.org/10.1190/1.9781560801580
ISBN	ISBN 978-1-56080-094-1
Store	SEG Online Store

It is important that we revisit the processing sequence in Figure 3.3-12 and the near-surface model depicted in Figure 3.4-10 for a rigorous description of moveout and statics corrections. Starting with unprocessed field records, a detailed version of the processing sequence in Figure 3.3-12 is described below:

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  Figure 3.3-12  Processing flowchart with residual statics corrections.

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  Figure 3.4-10  A near-surface model for statics corrections when shots are situated below the weathering layer. Here, S = shot, E_S = elevation at the shot station on the ground, R = receiver, E_R = elevation at the receiver station on the ground, T = surface topography, B = base of weathering, D = datum, E_D = datum elevation, v_w = weathering velocity, and v_b = bedrock velocity.

1. Pick and edit first breaks from unprocessed field records.
2. Assume or derive from uphole information a value for weathering velocity.
3. For a downhole source, apply the uphole correction.
4. Compute the bedrock velocity and intercept times at all shot and receiver stations using a refraction statics method, such as the generalized reciprocal or the least-squares technique.
5. By using the weathering velocity, bedrock velocity and intercept times, compute the depth to bedrock at shot-receiver stations (equations 53a, 53b).
6. Apply the shot and receiver statics to replace the weathering layer with the bedrock while placing the shot and receivers on a floating datum that corresponds to a smoothed form of the topographic surface. The static time shift Δτ_ij to apply for a given source-receiver pair is (Figure 3.4-10)

$T_{j}={\frac {z_{j}{\sqrt {v_{b}^{2}-v_{w}^{2}}}}{v_{b}v_{w}}},$

(53a)

$T_{i}={\frac {z_{i}{\sqrt {v_{b}^{2}-v_{w}^{2}}}}{v_{b}v_{w}}}.$

(53b)

$\Delta \tau _{ij}=(z_{j}+z_{i})({\dfrac {1}{v_{b}}}-{\dfrac {1}{v_{w}}})-{\dfrac {1}{v_{b}}}\left(E_{Tj}-E_{FDj}+E_{Ti}-E_{FDi}\right),$

(54a)

where z_j and z_i are the thickness of the weathering layer at shot and receiver stations, E_Tj and E_Ti are the true shot and receiver elevations referenced to the topography, and E_FDj and E_FDi are the shot and receiver elevations referenced to the floating datum, respectively. The reason for moving the shots and receivers to a floating datum close to the surface topography, rather than to a flat datum, is to be able to preserve the hyperbolicity of reflection times while placing the shot and receiver pairs associated with a CMP gather over the local datum level that is nearly flat within the spread length.

1. Apply geometric spreading correction and deconvolution to shot records and sort to CMP gathers.
2. Perform preliminary velocity analysis and apply moveout corrections.
3. Apply datum corrections to move the shots and receivers from the floating datum as specified in step (f) to a flat datum E_D to which the CMP stack is referenced. Refer to Figure 3.4-10 and note that the datum correction Δτ_ij for a source-receiver pair is given by

$\Delta \tau _{ij}={\frac {2E_{D}-(E_{FDj}+E_{FDi})}{v_{b}}},$

(54b)

where E_FDj and E_FDi are the shot and receiver elevations with respect to the floating datum specified in step (f).

1. Estimate surface-consistent shot and residual static shifts using methods described in Residual statics corrections.
2. Apply residual statics corrections to CMP gathers from step (i).
3. Apply the inverse of step (i) to move the shots and receivers from the flat reference datum back to the floating datum.
4. Apply inverse moveout correction using velocities from step (h).
5. Perform velocity analysis and apply moveout correction.
6. Apply datum corrections to move the shots and receivers from the floating datum to the reference flat datum as in step (i).
7. Apply mute and stack the data. The stacked section is referenced to the flat datum level E_D specified in step (i).

See also

• First breaks
• Field statics corrections
• Flat refractor
• Dipping refractor
• The plus-minus method
• The generalized reciprocal method
• The least-squares method
• Model experiments
• Field data examples
• Exercises
• Topics in moveout and statics corrections

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