Free Online Seismic Well Tie Tool: Synthetic Seismogram from LAS to SEG-Y

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Load the demo, or open a LAS file with sonic and density curves. Add a SEG-Y file to tie against real data. Everything stays in your browser.
Left trace: the synthetic seismogram built from your sonic and density logs (impedance, reflectivity, then convolution with a Ricker wavelet). Right trace: the seismic at your chosen trace. Drag the bulk shift until events line up, or press Find Best Shift to scan for the maximum cross-correlation. A correlation above about 0.6 over a few hundred milliseconds is a usable tie; above 0.8 is a good one.

Why the well tie is the most important step in interpretation

Every horizon an interpreter picks on seismic is a claim about geology, and the well tie is the only place that claim gets tested against ground truth. The tool above performs the classic tie workflow in your browser: it reads sonic and density curves from a LAS file, converts depth to two-way time by integrating the sonic, computes acoustic impedance and the reflectivity series, convolves with a Ricker wavelet to build the synthetic seismogram, and then lets you slide that synthetic against a real trace from a SEG-Y file until the events line up. A live cross-correlation coefficient scores the match, and Find Best Shift scans the whole range for you.

Workflow diagram of a seismic well tie: sonic and density logs from a LAS file are converted to a synthetic seismogram, shifted, and compared against a SEG-Y seismic trace to produce a correlation coefficient
The well tie: logs become a synthetic, the synthetic is matched to the seismic, and the correlation says how good the tie is.

This is the third tool in the Geoscience Workbench and the bridge between the first two: the LAS viewer reads the well, the SEG-Y viewer reads the survey, and the tie connects them. Load the built-in demo to see a working tie immediately, then bring your own files. As with every Workbench tool, both files are parsed locally and never leave your computer.

How the synthetic seismogram is built

The sonic log measures transit time, so integrating it downward accumulates travel time: each half meter of rock adds its slowness, doubled for the two-way path. You anchor the conversion by entering the two-way time at the top of the log, which stands in for the checkshot most real ties start from. Impedance is velocity times density (a constant 2.3 g/cc fills in if your file has no density curve), reflection coefficients come from impedance contrasts resampled to seismic time, and the wavelet slider lets you match the bandwidth of your actual data. If your sonic is in us/m rather than us/ft, switch the units selector.

Reading the tie

  • The correlation coefficient is the score: above about 0.6 over a few hundred milliseconds is usable, above 0.8 is a tie you can hang a prospect on.
  • A good match at the wrong shift is the classic trap. If Find Best Shift lands more than 40 or 50 ms from zero, question your datum time before trusting the shift.
  • If character matches but polarity looks flipped, your seismic may follow the opposite polarity convention; recognizing that is half the tie.
  • A tie that is good at the top and drifts with depth usually means the sonic needs a stretch, which is what checkshots correct in full workstation ties.

What this tool is for

Teaching the tie, checking a tie someone else claims, and getting a first-pass time-depth relationship when all you have is a LAS file and a SEG-Y line. It applies a single bulk shift rather than the multi-point stretch and squeeze of commercial packages, and it builds its wavelet analytically rather than extracting one from the data. Those are the right simplifications for a browser tool: they keep the physics honest and the workflow transparent, which is exactly what the learning version of a well tie should be.

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