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The Set update filter option is available for excluding wells that obviously has wrong starting velocities, namely the sound velocity in water.
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Checkshot wells organized in a folder
Sometimes the checkshot wells must be generated by merging velocity and time from one dataset into the well position of another dataset. That is done by the command object Merge x y with two data parameters found under schema type Line folder utilities. Set your folder with well positions to that schema type, or copy the command object from the repository into Item Commands on that folder. Then one can generate the proper checkshot wells from separate well data information.
When reading the checkshot wells into the algorithm, all wells are collected into one dataset. This dataset is also transformed into x y two_way_time velocity so it will match the velocity cube. All checkshot wells are prolonged to go from cube_min to cube_max in order to produce matching data all along the well string. The transformed and prolonged checkshot wells are saved in workspace data as updatedwells and can be further inspected.
The default updating algorithm is called Moving average which means that the differences from the checkshot slice and cube slice are gridded with a moving average interpolator and added to the cube slice.
The Tensor algorithm uses a bell shaped b-spline tensor for updating and is recommended for a local updating around well. A counter for each layer is listed on the terminal window during updating.
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| After updating the cube with checkshot wells the cube should be displayed and checked that the cube layers are matching the well data. The above figure shows that the cube matches according to the color code of the checkshot wells by displaying the bottom layer before updating the cube (to the left) and after updating the cube (to the right). After smoothing and updating the velocity cube it can now be used for depth conversion. Depth conversion using a dedicated command object
The velocity cube is useful for depth conversion of time grids into depth grids. This formula is used: depth_grid = time_grid x velocity_of_time_grid The size of the cube in z direction should be at least a little bit greater than the extent of the top and bottom surface. Then all the surfaces will fit into the velocity cube. |
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Transformed checkshot wells with bottom layer before and after updating cube
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Checking the cube visually
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| The velocity cube is displayed by dedicated commands available through the Cube schema.
Upper left viewport shows surface contours for the cube using the comannds commands Cube contours. Upper right shows planes in the cube colored and contoured with velocity using Cube views->Map X Y Z planes at cursor position. That command requires a cursor position inside the cube frame which can be set hitting the keyboard letter p or y while pointing at the screen. Bottom left is a cube overview contoured as a boundary surface using Cube contours. Bottom right is cube layer at level 4400 displayed as terrain using Display selected cube layers. This menu allows for displaying single cube layers or arranges multiple layers in viewports if this option is checked in on the Viewport display setup page. Displaying individual layers in a cube is important for checking the cube contents and also for presentation purposes. |
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Transformed checkshot wells with bottom layer before and after updating cube |
Displaying velocity cube with three planes and transparent surface boundary
Various ways to display cube information
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