From the Kirchhoff PreSDM Migration TT module we get the PreSDM CIGs. We take them as an input to PSDM Imaging and run our next iteration of velocity to update our model.
Inputs:
1. PreSDM CIGs
2. Initial velocity model
Outputs:
1. Updated velocity model
2. Time CIGs
3. Time RMO CIGs
4. Depth processed CIGs
5. Depth processed RMO CIGs
5. Depth stack
6. Time stack
7. Time to depth converted stack
8. Angle stack
PSDM Imaging:
In PSDM Imaging, the user can to perform various tasks like updating the velocity model, picking the delta Vrms from the Delta Vrms semblance and correct/flatten the gathers, mute picking on the CIG gathers, Create output CIGs, Create final stacks etc. To display the vista items, the user should right click on the PSDM Imaging and select Vista Groups followed by All groups.
PSDM Imaging-> right click->Vista Groups->All Groups->In new window.
The user can pick these Delta Vrms at specified interval. Also the user can choose between automatic and manual picks.
In the above image, we have CIG Depth gather and the corresponding CIG depth expected gather after performing the Delta Vrms picking on the adjacent Delta Vrms semblance view. On the far right hand side we can see the location map with predefined Delta Vrms picks locations.Once all the picks were completed on the Delta Vrms semblance as per the user's satisfaction ,the user can update the velocity model by selecting the option "Correct velocity model by delta Vrms picking" on the action items as shown below.
After selecting the "Correct velocity model by delta Vrms picking" option, it generates the updated depth velocity model. It can be displayed by right clicking on the PSDM Imaging module -> Vista Groups-> Updated depth velocity.
In the below image, we can see the initial and updated depth velocity model after done picking the delta Vrms on the Delta Vrms semblance.
Parameters:
Current horizon If the user input the picked horizons to the PSDM Imaging, it displays the current horizon.
Output time ratio(ms) Specify the output time ratio of time image gather
Output time length(ms) Specify the output time length of time image gather
V0 (m/s) Provide the near surface/replacement velocity
Output datum(meter) Provide the output datum value
Use mute Default it is TRUE. If the user picks any mute on the CIG gathers then it will applicable on the output gathers.
Use RMO By default it is TRUE. If the user prefers to use this option Residual Move Out to correct the gathers
Use Super gather By default TRUE. It is mainly used in calculating the Delta Vrms semblance.
Super gather aperture(meter) The user can define the aperture by considering the bin center to the maximum offset range.
Normalize migration
Accuracy Depending on the quality of the travel time table, the time image gathers are more or less accurate. For example, if the TT table is more accurate then the time image gathers converted from the depth imaging gathers will be more accurate
Stack creation bulk size While creating the stack, it processes the number of traces in a bulk. Provide an appropriate bulk size. Default value works good enough..
Arbitary line Parameters
Create arbitrary line The user can create/draw an arbitrary line on the location map and it will create the stack(s) of the arbitrary line.
Arbitary line step(meter) Distance between the neighbor bins from the arbitrary line.
Create tomo parameters
Use delta Vrms picks By Default TRUE.
Bin step to create parameters
Plus delta Vrms
RT Type
Angle aperture(degree)
Find Step X(meter)
Find Step Y(meter)
Time Step(ms)
Map Interpolation
Interpolation step X(meter) It basically interpolating the horizon maps. So the user can provide the step size in X direction to interpolate the horizons
Interpolation step Y(meter) Provide the step size in Y direction to interpolate the horizons.
Markers option
Marker accuracy(meter) It is the distance between the neighbor bin and the well marker. If the distance between the bin and well marker is greater than the user actual value of the marker and the bin, this well marker won't attach to this bin. However if the distance is close to the well marker and neighbor bin, it will attach to the bin.
Usually the bin grid size is sufficient enough for the marker accuracy to consider this well marker to the neighbor bin.
Well tie options
Marker distance(meter) Here we are tying the wells with the neighbor bin. The user should provide the maximum distance to consider this well to tie the neighbor bin.
Add bottom layer By default TRUE. It will create/add a bottom layer(horizon) to the last sample of the well.
Number of iterations It is an iterative process by tying the wells to the neighbor bins thus we build the velocity model close enough with the well tie markers. The more iterations the better result.
Minimum velocity(m/s) Minimum velocity for the velocity model building
Maximum velocity(m/s) Maximum velocity for the building the velocity model
Gradient type We have two options. Smooth and Simple
While updating the velocity model and let's say we have two layers and the interpolation between these two layers is by means of multiplication of the velocity sample between these two layers with a coefficient. This coefficient changes from constant values to a different values in between these two layers.
Simple- if the coefficients are constant values between these two layers the gradient is simple
Smooth- if the coefficients are varying with different values, then it will do a linear interpolation and smooth it. It is a smooth gradient type.
Interpolation type This is interpolation of the velocities and the coefficients by using Voronoi or ABOS methods.
Maximum distance to veronoi interpolation
Extrapolate deepest layer coeef
Extracting picking parameters These parameters are used to smooth delta Vrms picking.
Use smooth for delta Vrms picking gather By default FALSE.
Delta Vrms smooth X(meter) Smoothing distance in X direction
Delta Vrms smooth Y(meter) Smoothing distance in Y direction
Delta Vrms smooth Z(meter) Smoothing distance in Z direction
Depth velocity correction parameters We are building the system of equations(by tying the Delta of Interval velocity to the Delta Vrms using DIX formula) to update the velocity model by Delta Vrms picking. The unknown variables are velocities along the grid i.e. X,Y and Z.
Variables grid step X(meter) Provide the variable grid step in X direction to compute the unknown variable i.e.Delta Interval velocity
Variables grid step Y(meter) Similarly the grid step in Y direction to compute the unknown variable i.e. Delta interval velocity
Variables grid step Z(meter) In the Z direction to compute the unknown variable i.e. Delta interval velocity
Equations step inline This is basically grid of equations to update the velocity model along inline, cross line and in depth(Z) direction. Provide the inline step/grid size
Equations step cross line Provide the cross line step/grid size.
Equations step samples This is along the depth(Z) direction. Provide the step/grid size.
Regularization weight X If the regularization in X direction is higher in value then the solver will make the velocities of the neighbor samples in X direction as close as possible.
Regularization weight Y Similarly in Y direction, the solver makes the velocities of the neighbor samples as close as possible
Regularization weight Z Same as in X & Y directions.
Freeze velocity above this depth(meter) Not changing the velocities above the user specified depths to keep them as it should be.
Freeze weight The bigger the weight the more probability of not changing the velocities.
Max number of iterations Number of iterations to perform the solving parameters to update the velocity model.
Solve equations with limitations on delta V This parameter limits the maximum interval velocity update. If the user chooses this option, the interval velocity update can be limited by the parameter "Max allowed relative delta V"
Max allowed relative delta V(%) Specific the % relative delta to limit updating the interval velocity. It depends on the initial velocity model.
Apply limitations every iteration If the user checks this option, it will limit updating the interval velocity for each iteration.
Multiplier for delta V(%) Default value is sufficient
Smooth updated velocity model If the user wants to have a smooth updated velocity without any perturbations they can check this option.
Update model smooth X(meter) Provide the smoothing distance in X direction
Update model smooth Y(meter) Similarly in Y direction of smooth distance
Update model smooth Z(meter) Smoothing distance in Z direction
Delta Vrms semblance params
Use average semblance from bins of super gather If the user select the super gather option, it will calculate the semblance based on the super gather aperture. This will gives us the good semblance and cancels out any noise present in the semblance display if the user takes a bigger super gather apertures.
Delta Vrms min(m/s) Mimimum delta Vrms value
Delta Vrms max(m/s) Maximum delta Vrms value
Delta Vrms step(m/s) Step value of delta Vrms
Auto picking start depth(meter) If the user prefers to pick the delta Vrms by using the auto picking delta Vrms option from the action items, they can provide the starting depth of the user preference rather than starting from Zero(0) depth.
Auto picking depth step(meter) At what depth interval the auto picking of delta Vrms should pick
Auto picking trace step(trace) This option is for 3D case. It acts like a decimation where the user can define the trace step size to auto pick the delta Vrms.
Auto picking threshold Depending on the auto picking depth step, the auto picking picks the delta Vrms based on the auto picking threshold value. If the auto picking threshold value is greater than the semblance value then the auto picker doesn't consider these picks within the auto picking depth step.
Use corridor for auto picking The user can pick the corridor and the auto picker will consider the semblance values in this corridor to pick the delta Vrms.
Corridor width on click(m/s) The distance from the picking position to both sides of the picking location of the corridor.
Use smooth for auto picking Provide the smoothing to the auto picking
Smooth window for auto picking(meter) The more the smooth window the result of the auto picks of the delta vrms are smooth.
Limit residuals If the user checks this option, it can limit the residual of the time shift in the far offsets to a certain extent as defined by the user
Max allowed residual on max offset(meter) This value determines how much is the maximum shift allowed in the far offset
Inversion tolerance for auto picking By default it is FALSE. If the user checks this option it will calculate the inversion tolerance depending on the Delta V and Delta Z values.
It calculates the ratio of Delta V/ Delta Z for a line segment on the Delta Vrms auto picking semblance window. This ratio should be less than or equal to the Delta V/DeltZ ratio. The objective of this calculation is to avoid the zig zag pattern of the auto picking.
Delta V(m/s) Provide Delta V value as per the semblance
Delta Z(meter) Specify Delta Z value
Use semblance normalization By default it is FALSE. We divide the overall semblance panel in to different window lengths and each window is over lapped by half of the window length. Then we take the maximum amplitude within that window and normalizes each sample with this value. Then we average each sample from these windows to have a normalized semblance display.
Semblance normalization window(ms) Provide at what interval the semblance normalization window should take place.
Use semblance smooth Smoothing of the semblance matrix
Semblance smooth window(ms) Provide value for smoothing window for the semblance matrix
Import horizons from ASCII Parameters
Location Specify whether the horizon is on Topography or Datum.
Datum(meter) If the location is Datum the the user should provide the Datum value.
Scalar Scalar for the depth coordinates
Add constant shift(ms) Add constant shift value to the horizon
Add constant shift depth(meter)
Import coordinates scalar
Scalar Scalar for the coordinates
Well ties
Well tie parameters
Layer name Select the horizon from the drop down menu
Mark name If the user import the markers, they can to see the markers corresponding to the layer (horizon) name.
Angle stack params
Current angle This will display the current angle and the corresponding angle stack if the user generated the angle stacks from the action items "Recreate common angle stacks". This will display all the available angle ranges as it is specified in the below parameters.
First angle(degree) Starting angle for angle stack
Last angle(degree) End angle for angle stack
Step angle(degree) Angle step size
Angle smooth window length(samples) It will smooth the boundaries between the previous angle stack and current angle stack
Alternative By default it is FALSE however if the user checks this option, it will consider the Vrms velocities for creating the angle stacks.
Interpolated Params
Wells