From my understanding 25% CoS is considered the norm for...

From my understanding 25% CoS is considered the norm for conventional wells....so our Winx is sitting on the statistical average. The calc for deriving CoS is based on a few factors multiplied by each other, to get the final CoS.  Brom posted an excellent video on risk assessment for oil a couple of days ago...definitely worth a listen if you have a spare hour or so (see below).

Alternatively, you can cut to the chase at about 26:15 minute stage to see the actual calc parameters....but the richness/complexity behind each of the 6 variables is discussed earlier.  Here is a snapshot of the key slide:


With R, S and T representing the Reservoir Rock, Source Rock and Seal/Trap respectively and the little "p" and "e" representing "presence" and "effectiveness".  Hence Rp is the probability that the Reservoir Rock is present and Re is the probability that the Reservoir Rock is effective (eg permeability, porosity etc).

Bear in mind....if each of the six variables has a high probability of 80%, then multiplying them all together results in a CoS of about 25%. Interesting!

Here is the video shared earlier by Brom:

GLTA.