An explanation10 Sep 2018 18:41
One guy called Steve posted this explanation on another board, hope it some help to some of you. It was to me.
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If they've been coring all the way down (or at least the bottom 1000m or so, then this would partly explain the long time to drill.
Coring (where they need to pull the entire drill-string out of the hole in 20-30m sections to recover each cored segment of 20m or so in length) takes MUCH MUCH longer than simply circulating out the cuttings, and adding more drill pipe at the surface to keep going deeper.
Coring at 1000m will entail removing 30-50 sections to get the last cored piece, then dropping it back down again... perhaps need to do this 50 times to get to 2000m, by which time they'd be recovering 60-1000 sections of upper drill-pipe...throw in a few stuck-pipes and no wonder it took so long.
Big question is: Did they really need to fully core it?