# Difference between revisions of "Processing sequence for statics corrections"

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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: | 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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+ | <gallery> | ||

+ | file:ch03_fig3-12.png|{{figure number|3.3-12}} Processing flowchart with [[residual statics corrections]]. | ||

+ | file:ch03_fig4-10.png|{{figure number|3.4-10}} A near-surface model for statics corrections when shots are situated below the weathering layer. Here, ''S'' = shot, ''E<sub>S</sub>'' = elevation at the shot station on the ground, ''R'' = receiver, ''E<sub>R</sub>'' = elevation at the receiver station on the ground, ''T'' = surface topography, ''B'' = base of weathering, ''D'' = datum, ''E<sub>D</sub>'' = datum elevation, ''v<sub>w</sub>'' = weathering velocity, and ''v<sub>b</sub>'' = bedrock velocity. | ||

+ | </gallery> | ||

# Pick and edit [[first breaks]] from unprocessed field records. | # Pick and edit [[first breaks]] from unprocessed field records. | ||

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# By using the weathering velocity, bedrock velocity and intercept times, compute the depth to bedrock at shot-receiver stations (equations {{EquationNote|53a}}, {{EquationNote|53b}}). | # By using the weathering velocity, bedrock velocity and intercept times, compute the depth to bedrock at shot-receiver stations (equations {{EquationNote|53a}}, {{EquationNote|53b}}). | ||

# 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 Δ''τ<sub>ij</sub>'' to apply for a given source-receiver pair is (Figure 3.4-10) | # 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 Δ''τ<sub>ij</sub>'' to apply for a given source-receiver pair is (Figure 3.4-10) | ||

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+ | {{NumBlk|:|<math>T_j=\frac{z_j\sqrt{v^2_b-v^2_w}}{v_bv_w},</math>|{{EquationRef|53a}}}} | ||

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+ | {{NumBlk|:|<math>T_i=\frac{z_i\sqrt{v^2_b-v^2_w}}{v_bv_w}.</math>|{{EquationRef|53b}}}} | ||

{{NumBlk|:|<math>\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),</math>|{{EquationRef|54a}}}} | {{NumBlk|:|<math>\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),</math>|{{EquationRef|54a}}}} |

## Latest revision as of 10:41, 19 September 2014

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:

**Figure 3.3-12**Processing flowchart with residual statics corrections.**Figure 3.4-10**A near-surface model for statics corrections when shots are situated below the weathering layer. Here,*S*= shot,*E*= elevation at the shot station on the ground,_{S}*R*= receiver,*E*= elevation at the receiver station on the ground,_{R}*T*= surface topography,*B*= base of weathering,*D*= datum,*E*= datum elevation,_{D}*v*= weathering velocity, and_{w}*v*= bedrock velocity._{b}

- Pick and edit first breaks from unprocessed field records.
- Assume or derive from uphole information a value for weathering velocity.
- For a downhole source, apply the uphole correction.
- 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.
- By using the weathering velocity, bedrock velocity and intercept times, compute the depth to bedrock at shot-receiver stations (equations
**53a**,**53b**). - 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 Δ
*τ*to apply for a given source-receiver pair is (Figure 3.4-10)_{ij}

**(**)

**(**)

**(**)

where *z _{j}* and

*z*are the thickness of the weathering layer at shot and receiver stations,

_{i}*E*and

_{Tj}*E*are the true shot and receiver elevations referenced to the topography, and

_{Ti}*E*and

_{FDj}*E*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.

_{FDi}- Apply geometric spreading correction and deconvolution to shot records and sort to CMP gathers.
- Perform preliminary velocity analysis and apply moveout corrections.
- Apply datum corrections to move the shots and receivers from the floating datum as specified in step (f) to a flat datum
*E*to which the CMP stack is referenced. Refer to Figure 3.4-10 and note that the datum correction Δ_{D}*τ*for a source-receiver pair is given by_{ij}

**(**)

where *E _{FDj}* and

*E*are the shot and receiver elevations with respect to the floating datum specified in step (f).

_{FDi}- Estimate surface-consistent shot and residual static shifts using methods described in Residual statics corrections.
- Apply residual statics corrections to CMP gathers from step (i).
- Apply the inverse of step (i) to move the shots and receivers from the flat reference datum back to the floating datum.
- Apply inverse moveout correction using velocities from step (h).
- Perform velocity analysis and apply moveout correction.
- Apply datum corrections to move the shots and receivers from the floating datum to the reference flat datum as in step (i).
- Apply mute and stack the data. The stacked section is referenced to the flat datum level
*E*specified in step (i)._{D}

## 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