Old CBIL data - why you should review it.

So first, if you are still here I imagine you know what I am talking about, if not a boring industry specific article follows and I would leave now or consider the following an insomnia cure,

The CBIL was launched by Atlas Wireline as an acoustic borehole televiewer. In short a rotating acoustic transducer taking 250 samples per revolution generated a couple of images of the borehole. One being the acoustic impedance which reflected changes in the rock fabric itself and the second being the travel time which reflected the time it took to send and receive the signal and basically gave you the size of the borehole once calibrated. In the early 90s the original CBIL (known internally at Atlas Wireline as the Analog CBIL) was replaced by the digital CBIL tied in to their new Eclips acquisition system. I am concentrating first on those early analog CBILs and things are about to get a lot more technical. Then I will come back to the digital CBIL.

Within the CBIL tool itself was a magnetometer pack which was used to orient these tools to "Downhole Magnetic North". The earliest runs were performed with just this for orientation and later runs included a complete separate orientation sonde (known as a 1016). It is the runs with the 1016 which are of interest here.

The first reason for adding the 1016 was to improve orientation because it had independent orientation magnetometers and accelerometers. All CBIL tools had a mark on them known as the "Tool Body Mark", The 1016 had a pseudo Pad 1 aligned to this mark and often grease was smeared over the teflon window inline with this mark, so what the 1016 recorded as pad 1 position also matched up to the CBIL tool. So during processing this would be checked and if there was a difference the CBIL would be rotated to line up and thus the orientation confirmed.

Some time later, the obvious was realised. The 1016 had an accelerometer pack, so you could speed correct analog CBILs. This bought a problem to light. When we started to speed correct the CBILs we found the 1016 data sometimes had been delayed during acquisition and needed shifting back to the CBIL depth reference point. This meant that the data used for the orientation check was in the wrong place depending on rotation of the tool, so ironically something put in place to confirm orientation often in fact resulted in an incorrect orientation of the data and hence a bad interpretation. Does the stress on your CBIL data not match the local stress regime? This may be the answer.

The digital CBIL data sometimes had fixable problems too. It may have been recorded in "Magnetometer Mode" and have a bad orientation, this can be fixed by switching the data out to "Tool Body Mark Mode" and re-orienting it. Was it recorded in "Tool Body Mark Mode" and have a bad orientation? It can be switched back to "Magnetometer Mode" and if the magnetometer in the CBIL was good a correct orientation can be obtained.

So if you have old CBIL data which was written off, maybe it is time to get it reviewed and get a better interpretation of that old data as there are valid reasons why it may be wrong and they can be fixed. There are other issues which can be fixed too, for example early speed corrections sometimes failed, a strong filter on the deviation curve often solved these, but some slipped out before this was realised.

What if you have CBIL data and no digital data? We can take the field prints, PDFs or reports and digitise the data back to a DLIS file for loading in any interpretation software. Of course we would rather work with digital data, just do not write off those old logs yet, we can give an unbiased opinion on what you have for a low fee and if we move ahead with any processing work we will subtract that fee from the processing costs. Please feel free to contact me for more information and grab a coffee to wake yourself back up if you made it this far.