FAQ¶
Traces and formats¶
Which trace files can I upload?
SEG-2 (.sg2, .seg2, .dat) and text files with the traces in columns (.txt, .csv).
Each file up to 20 MB. See Traces and time picking.
My format is not among them. What do I do? Downhole NX does not read SEG-Y or the proprietary formats of acquisition instruments. Two ways out: export the traces from the instrument software to SEG-2 or text, or read the times elsewhere and enter them in the Measurements tab. Processing starts from the times: traces are not required.
A SEG-2 file is rejected with “Unsupported SEG-2 data format”. The app reads SEG-2 samples as 16- and 32-bit integers and as 32- and 64-bit floating point. The 20-bit floating-point encoding is not read: export the file in another encoding.
The P-shot and S-shot files have a different number of channels. The app warns you and does not merge them: channels are read by number. Check P-wave channel and Channels per geophone, or export the files again with the same number of channels.
I have a large survey. Are there limits?
A project holds up to 600 files, 400 depth rows and 64 channels. Files are uploaded in
batches: if the server rejects an upload because it is too large, upload fewer files at a
time. In the .dhnx file traces fit up to 30 MB in all; beyond that the file carries the
references, and the traces are uploaded again on reopening. Always keep the original files.
See Files.
I uploaded the files but the plot is empty. The depths are missing. Type those of the first two rows in the Depths and files card: the others take the step.
The depths assigned to the files are wrong. Grouping follows the order of the names. Check S-wave shots (1 or 2), correct the cells by hand, or press Group again after changing the options.
Can I trust the proposed times? As you would a first reading made by someone else: all of them must be looked at again on the traces. On the sample survey the proposal on P waves is within about half a millisecond of the manual pick; on S waves within a few milliseconds, with the largest deviations at the shallowest depths. Start with the times marked “?”, but look at the others too. See Proposing the times.
Why are so many S times doubtful? Because the shear wave arrives inside the tail of the P waves and its first arrival is less sharp. The app marks a time as doubtful when it deviates from the trend of the neighbouring depths, when it does not increase with depth or when the signal is weak: on S waves that happens often. “Doubtful” does not mean wrong, it means to be looked at.
How do I remove the “?” from a time I have checked? Pick it yourself: switch on Tp or Ts and click on the trace, even at the same point.
Does having times or seismic layers proposed use credits? No, with the buttons in the tab it is free. If you ask the assistant, you pay for the message.
Measurements and calculation¶
I only have S waves (or only P waves). Can I process the test? Yes. Leave at zero the times of the wave you do not have: zero means “not measured”. The columns of that wave show “--”; with S waves alone you get Vs, G and Vs,eq, while ν, Ed, E and Ev also need Vp.
A time is missing at one depth. Leave it at zero. The two intervals touching that receiver stay “--” for that wave; in the direct method the times at the layer bases are interpolated on the measured receivers.
What does “--” mean? “Cannot be computed”, not zero: a time is missing, the corrected time does not increase between two receivers, or Vp and Vs do not give a Poisson's ratio between 0 and 0.5.
Where is the “Calculate” button? There is none. Processing updates at every change and is free.
I move the seismic layers but Vs,eq does not change. Is that a bug? No. In the direct method the sum of the travel times through the layers is the corrected S-wave time at depth H, wherever the bases are. In the interval method Vs,eq is computed on the measurement intervals. It changes only if the test is shorter than H: there the last layer is extended, and its velocity depends on the base just above it. See Processing.
Are the proposed seismic layers the stratigraphy of the site? No. They are the subdivision that best follows the corrected times, with bases on the measurement depths. Use them as a starting point and move them where the borehole log and your reading of the travel-time curve require. See Proposing the seismic layers.
I set 40 m as the final depth and the label still says “Vs,30”. With a final depth of 30 m or more the label is Vs,30, but the value is the one between the two depths written in the note below the number. For Vs,30 leave 0 and 30.
The test stops at 20 m. Can I get Vs,30? The app extends the last layer to 30 m and says so on screen and in the report. It is an assumption: it is for you to judge whether the velocity of the last layer can be extended.
Does the program tell me the subsoil category? No. Vs,eq is a number; the category takes the depth of the bedrock and is left to the designer.
Can I use the moduli for settlements? Not directly: they are dynamic, small-strain moduli.
Is the unit weight measured or estimated? With the switch on it is estimated from a correlation with Vs and depth. If you have measured values, switch it off and type γ in the table. See Measurements.
Desktop version¶
I open the same desktop project and the numbers are different. Why? Downhole NX fixes some calculation defects of the desktop program. The differences are in precise places: velocity of the last layer, γ and moduli of the direct method, Vs,eq of the interval method and of tests shorter than H. Corrected times and values per interval match. The full table, with reason and effect, is in Validation and differences from the desktop version.
Can I save to .dwhx to reopen in the desktop program?
No. Downhole NX opens desktop files but saves only to .dhnx.
After opening a .dwhx the traces are not there.
The desktop project does not contain them. Upload the SEG-2 files again in the Traces tab.
Session, files and credits¶
I left the app open and now it says “The session has expired”.
After 30 minutes of inactivity the project is no longer in memory. Nothing was written or
charged: reopen your .dhnx. Save often. See Files.
“The project was modified in the meantime”. The assistant or another browser tab changed the project. Reload the page: what you had on screen was not saved.
What uses credits? Generate Word, Export DXF and each message to the assistant. Everything else is free.
Was I charged for a failed operation? No. Credits are charged only when the operation succeeds.
In which language is the report? Can I have it as a PDF? In the interface language: switch it before generating. The format is Word; you get the PDF from your word processor.
Does it work on a tablet or with Safari? The app is tested with Chromium-based desktop browsers and windows at least 900 px wide. Touch dragging and Safari have not been tested.
Found an error on this page? Let us know or open a Pull Request.