From what I've read so far it seems people have really looked and we have some estimates (not yet proven reserves). The highest estimates I found are around 10-20 years of current consumption rate. That doesn't seem like a lot, and Europe's consumption is going down so it doesn't feel like this will change much for shale oil.

But Norway still has big gas reserves and supplies 33% of Eueropian consumption, so I was actually wrong in the original comment and the US LNG impact is pretty overstated, it's just 15%. Most of the rest comes from middle east.