[agapos]

The currently mined gas deposits in Siberia are at least 600 meters below the ground level, normally deeper (generally at 1-2 km). The thickness of permafrost in most areas is a few ten meters, with the more cold areas reaching 300-450 meters, so there little to no overlap between the two.

This PDF contains a few numbers for those interested: http://www.arlis.org/docs/vol1/ICOP/40770716/CD-ROM/Proceedi...