OpendTect dGB Plugins User Documentation version 3.2
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3.2. Data Preparation

Before chronostratigraphy is calculated, the data must be prepared. Specifically, horizons must exist everywhere, they cannot cross each other, instead, they should truncate against each other as and where appropriate. For these purposes, utilities exist to fill up holes and check crossings respectively.

Also, for the data driven chronostratigraphy computations a smooth dip-azimuth field is needed. This can be achieved by median filtering the SteeringCube.

3.2.1. Horizon preparation

To resolve conflicts with crossing horizons, select check crossings sub-menu (SSIS - Data preparations - Horizons - Check crossings). The Horizon relation window pops up. Select all horizons that need checking (Read Horizons ...). The horizons are sorted automatically from top to bottom. Now press Check crossings...

To solve crossing conflicts select the horizon that will be modified. The software will check the number of positions where a conflict exits and modify the horizon by removing the conflict points or by changing the values to be equal to the overlying/underlying horizon.

Note: To honor the requirement that horizons cannot coincide, the actual values are not exactly equal, but they are within one sample position accuracy.

The figure below sketches what will happen to horizon B if you select shift (1) or remove (2). Figures (3) and (4) show the results for shifting (3) and removing (4) when horizon A is the one to be modified. The software verifies that removing and shifting operations are executed properly and the correct chronostratigraphy calculation results are reached.

Holes in horizons can lead to unexpected chronostratigraphy results. It is, therefore, recommended to work with continuous horizons. The fill holes utility using an iterative application of an inverse distance algorithm. In successive steps holes are interpolated which means that the algorithm stays local in each step.

The options are:

Extrapolate outward: If set to yes the horizon is extrapolated to match the dimension of the survey area, or specified work area, as the case may be.
Maximum fill size(nodes): In some cases, you do want to keep large holes. If so, select this option and set it to the maximum size in nodes you still want to be filled.
Fill Type: Two options are available. The first is Extension and the second is Gridding.
Maximum extension steps: Restricting the number of interpolation steps facilitates in partially filling the holes. This is useful when filling holes of a particular shape.
Save interpolated horizon: The horizon can be saved as new horizon or is overwritten.

3.2.2. Filtering the SteeringCube

The SteeringCube can be improved by smoothing. A better SteeringCube improves chronostratigraphy calculations. Use the option Filter SteeringCube... to apply a median filter to the SteeringCube. Adjust the needed parameters: inline/crossline step-out, time gate size, and maximum dip according to your dataset. Filtering of the SteeringCube is described in Section 2.2.3

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