Horizon auto-tracking

[مصطفى قاسم مطشر كلية العلوم / علم الارض‎]

Dear ِall,

I am working with a 3D seismic cube and trying to auto-track a specific horizon. The cube contains some gaps (areas not covered by the seismic survey).

I would like the horizon tracking to continue up to the end of the seismic line without creating artificial picks or interpolating across the gaps, only following the available seismic data.

Is there a setting or workflow in OpendTect that allows this?

Best regards.

Mustafa.

[Paul de Groot]

Hi Mustafa,

I'm surprised to hear that the tracker does not stop automatically at the gaps in your data. Seismic data sets typically mark gaps with traces flagged as undefined. The amplitude values of these traces are also set to 1e30 (OpendTect's undefined value, aka "undef"). Please check if the values are undefined (you can see the values in the lower left corner of the main window if you hover over a gap). 

If the values are not undefined the tracker may or may not stop at a gap. This depends on the tracker settings. To ensure it always stops, consider replacing all hard zeros by 1e30. This can be done via a mathematics attribute with the equation: "seis == 0 ? 1e30 : seis", where seis is your seismic data set.

I hope this helps. 

Best regards,

Paul.

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Paul de Groot

Special Adviser

-----------------------------------------------------------------------------------------------------------------------   dGB Earth Sciences
Phone: +31 53 4315155 E-mail: paul.d...@dgbes.com Internet: dgbes.com

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[مصطفى قاسم مطشر كلية العلوم / علم الارض‎]

Dear Paul,

Thank you for your helpful explanation.

However, as shown in the image below, I noticed that the tracker is picking a horizon in an area where no seismic traces exist (within the grey zone). This suggests that the tracking is continuing across the gap, even though there is no actual seismic data present in that region.

Could this behavior be related to how the gaps are represented in the data, or is there a specific tracker setting that might be causing this interpolation across the undefined area?

I would appreciate your guidance on how to prevent this and ensure that tracking stops strictly at the edge of available seismic data.

Best regards,

Mustafa 

[Paul de Groot]

Hi Mustafa,

I see two possible ways to get your image:

1. You used an inversion-based horizon tracker. These trackers create an output at every (live) trace position. It implies that the gap is not a real gap with flagged undefined traces. Instead it contains live traces, probably with hard zeros everywhere. You can test this by hovering your cursor over the gaps and checking the values in the lower-left corner. Alternatively, display a section in a 2D viewer with wiggles. Solutions: a) either reload the data without passing dead traces; b) or remove the area from the tracked horizon using the polygon removal tool.
2. You used the conventional amplitude & correlation-based auto-tracker. This tracker stops when it reaches the user-set constraints, therefore, your gaps should not have been tracked (even if these are live traces with hard zeros). To get your results, it seems you followed up with a gridding algorithm to fill the gaps. Solution: Use the "only holes" option in the "scope" parameter.

Best regards,

Paul.

--

Paul de Groot

Special Adviser

-----------------------------------------------------------------------------------------------------------------------   dGB Earth Sciences
Phone: +31 53 4315155 E-mail: paul.d...@dgbes.com Internet: dgbes.com

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