I can't imagine standing on a rig platform on a frozen lake... you would think that the vibration from the drill might compromise the ice, and then once you drill the mother hole, your time actually in it would be limited to the 3 or 4 months the ice would support the rig... not really a lot of time... and then the worst case scenerio would have the rig crew drilling from the lake bed should the ice give.... i'm sure that they charge more for that.

Unless they freeze a barge onto the ice or something....

Dan