Lundi Log 6 shows why log QC is important. In this example, we had a preexisting digital database (LAS files). We scanned the raster logs and then overlaid the digits on top of the raster image. You can see the LAS overlay near the right hand side of the log. Clearly the preexisting LAS file does not match the actual log and would be useless for any petrophysical analysis. Consider that in this field area the acoustic log had a phenomenal tie to core porosity (of course not so much in this specific log!). For this log interval, acoustic porosity derived from the original LAS digits significantly underestimated porosity—whereever the actual slowness curve lies to the right of the bad digits is missing porosity. After pointing out numerous other examples similar to this one, the client wanted us to redo their entire digital well database. The worse one was a neutron porosity log originally scaled from 0.45 to -0.15, rather than 45 to -15%, but I guess the original digitizer felt that it must be percent and made the really good rock with >20% look like it only had 0.2%. No QC and when company looked to perforate addition porous seams and not finding any, the well was plugged and abandoned. Yikes! Especially because the original perf’d zone that was perf’d based on the original paper log prior to log digitization showed only 0.2% or so too on the original digits! After 2.6 million curve feet of redigitization, I never wanted to be involved in a digitization project again! And thankfully I haven’t!