Statics - Surface Consistent

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Description

Surface-consistent residual static correction

Statics – Surface Consistent modules computes the source and receiver residual statics on surface consistent manner.

At the initial stages of the preprocessing, the poor SNR of CMP stack quality is due to the near surface velocity anomalies and topographic changes of the surface. These changes give rise to travel time shifts and it can be corrected by using various methods like refraction statics by means of picking first breaks and calculate the statics and apply them. Second method is Surface Consistent Residual Statics.

In the Surface Consistent Statics, it computes single static solution for all the traces that is coming from the same shot gather. In the case of receiver, separate statics corrections are applied for all the traces from the same receiver. For the combined statics correction, each trace coming from single shot and single receiver will have separate shot static and separate receiver statics. Combining these source and receiver statics give rise to single time shift or static correction.

In g-Platform, module Statics – Surface Consistent builds the pilot trace from the CMP stack based on the Model aperture (CMP) defined by the user at the Model & Stack Parametrization. For example if user input the Model aperture (CMP) as 1, it means there will be 3 traces for generating the model trace. There is one trace on the left of the center trace and one on the right side. As a first step, the center trace is cross correlated with the traces on both side of it and generates a model trace and stores in the memory and the process follows to the next trace and so on till to the last trace.

clip0110_r

In the above image, red trace acts as center trace and it do the cross correlation with the adjacent traces and generates the model trace. In the second stage of the surface consistent statics calculation, this model trace calculates the shift for the prestack gather of the CMP by means of cross correlating with the each individual trace.

clip0111_r

In the final step, we are solving the equations using Gauss Seidel in an iterative way to get the shifts for each individual shot and receiver gathers.

Within this module, we have Velocity Update parameter where in user can enable Velocity updates to automatically update the velocities with each iteration.

Parameters

Model & Stack

Model aperture

Number of CMPs in left and right directions in Cross line

Dip (msec/Tr)

Max CMP shift

Specify the maximum CMP shift value

Super bin aperture(sum near traces)

By default 1.

Use MF model

By default, FALSE. If this is checked, the user should provide the minimum, maximum dip values, Delta dip, Number of directions, Windows selection parameters

Minimum dip

Provide the minimum dip value

Maximum dip

Provide the maximum dip value

Delta dip

Number of directions

Windows selection

Calculation start time

Start time for statics calculation (visualized on stack section)

Calculation end time

End time for statics calculation (visualized on stack section)

Correlation length

The length of cross correlation function.

Maximum value depends on Max shiftparameter: if Correlation length<= Max shift*4, then Correlation length will be equal Max shift*4

Maximum static shift

Maximum static correction

Correlation threshold

Threshold value for correlation from 0-1, if the value will be less than defined, it will not be considered during calculation of statics correction

Number of iterations

Number of iterations of static corrections – cross correlation, solution, apply corrections

Number of Iteratively re-weighted solutions

Number of additional iterations – at each decision stage for the rapid convergence of distributed weight trace

Type

Select the type of calculation from the drop down menu. We have

SC statics shift - by default

SC phase rotation

SC statics shift and phase rotation

Phase rotation step

In case the Type of selection is SC phase rotation then the user should provide the phase rotation step size.

Trend removal

Remove trend

By default, TRUE

Grid size

Smooth

Advanced

CMP term

To stabilize the solution CMP term is used in the equation, but after the solution it excluded and is not used for the formation of effective static correction.

We have three options.

Don't use

Use residual

Use cross correlation - By default

CMP term correction window

If the CMP is used, then the user should provide the CMP term correction window.

Min Fold CMP

Specify the minimum fold CMP i.e. consider the CMP which are having a minimum fold of the user specified value. Any fold value below the user specified CMPs will be part of the statics compute.

Use a residual RMO term

To stabilize the solution residual NMO term is used in the equation, but after the solution it excluded and is not used for the formation of effective static correction

Use RMO limitation

By default TRUE

Use multi-maximum solving

By default FALSE

Use massive cross-correlation aproch

By default FALSE

RMO aperture

Aperture for smoothing the found Residual NMO (it used with “ Whether to use a residual NMO term in the Gauss-Seidel solution” parameter). “0” – will disable the smooth option

RMO minimum offset

Specify the minimum RMO offset.

Performance settings

Parameters for optimization of statics corrections

Max binning fold

Maximum fold. It used for automatic calculation of the size of data blocks that will be loaded into RAM

RAM cash size

Maximum amount of RAM allocated memory for the calculation of statics corrections. It used for automatic calculation of the size of the data blocks that will be loaded to RAM memory

Setup block size manually

Manual definition of the size of the data blocks to load to RAM. This automatically determines the required amount of memory

Block size Inline(CDP)

Block size in Inline direction

Block size Crossline

Block size in Crossline direction

Use cacher

By default, TRUE.

Visualization settings

Create stacks

By default FALSE. Check this feature to create stacks to visualize the stack response for each iteration

Show additional graphics every N iteration

Provide the number to display the stacks after each iteration. For example if user input 15 iterations then wants to see every 5th iteration, user needs to input 3 here.

Stacks for inline #

In case of 3D, the user can specify a particular inline

Stacks crossline #

The user can specify the crossline.

Velocity update

Enable velocity update

By default FALSE. Check this feature to automatically update the velocities

Create vrms models for iterations

By default FALSE. If checked, it will create the Vrms model

Velocity update each N iteration

By default 1. The user can define the number of velocity update iterations. If the user provides the same number of iterations as the residual statics stack iterations then it will generate the velocity as well stack for each iteration.

Corridor auto picking

Provide the velocity value for automatic picking

Auto picking trace step

Auto picking time step

Velocity increment

Semblance smoothing window

Stretch factor for auto-pick semblance

Normalization window

Smooth type

Select the appropriate velocity smooth type

Smooth window vertical direction

Specify the velocity smooth value (ms) in vertical direction

Smooth grid x direction

Specify velocity smooth (traces) value in X direction

Smooth grid y direction

Specify velocity smooth (samples) value in Y direction

NMO

Input gathers type

Select the appropriate input gather type from the drop down menu

1.NMO Gathers

2.Gathers without NMO

Vrms model

In case the user selected the Input gathers type as “Gathers without NMO” then provide the Vrms model

Stretch factor

Specify the NMO stretch factor

Smoothing parameter Y velocity

Shift to datum

By default FALSE, if checked then the user should provide the datum value in the next parameter