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ins.: 2014-08-26 00:00; ( Age: 10 yrs )
By: Scientists
Category: COSC1

COSC: 2014-08-26

The last drill core is up. Everything happened very quickly ...
A group photo after the last core came to the surface.

The last drill core is up. Everything happened very quickly during the last days. There wasn’t the expected 16+ hours break to change the drill bit - it lasted for 290 m until all “good” drill pipes were in the drill hole and the drill rig was at the edge of its capacity under the present technical circumstances. End of drilling. It takes some time to comprehend. Some numbers: COSC-1 TD is 2495.8 m (driller’s depth). According to the scientific documentation, we drilled 2393.1 m and recovered 2396.5 m of core + c. 2.5 m of documented core loss, both starting at 103 m (lower end of the conductor casing). The most likely explanation for the difference in TD/drilled length and depth according to documented core recovery (2502 m) is stretching of the drill pipes under their own weight in the drill hole, i.e. we have a core recovery of 100.14 %, despite of 2.5 m documented core loss. So where are we? Somewhere around 2500 m below the drill site and probably somewhere between 150 and 200 m besides it (a rough estimation based on the logged deviation at 1616 m and the angle measured by the Devicore BBT in the lower part of the well until we get precise data from logging). Geology: still present at the bottom of the drill hole. Mylonites, mylonites, mylonites. With garnets. But now mostly in meta-arkoses. Further studies will check this up and, hopefully, tell us more about the position in the tectonostratigraphy. Good to know that drill hole didn’t make a U-turn towards Åreskutan and the thrust zone below the Upper Sever Nappe! It’s far too early for conclusions, but some thoughts at the end of the drilling operations, after several months on-site: Completing the COSC-1 drill hole at about 2.5 km is a huge achievement, in particular with regard to the technical circumstances. A huge THANK YOU to drilling and technical teams! The rock quality in the area contributed to the amazing core recovery (never seen before by the drillers, not even in a shallow drill hole), although it seemed to eat drill bits in the Seve Nappe rocks. The on-site science was a huge effort - about 5 man-years (rough calculation). We never could have done this without the help of all the volunteers. A huge THANK YOU to the on-site science team, and in particular to all volunteers! About geology: We got an exceptional section through a high-grade metamorphic nappe and into the underlying thrust zone of a major mountain belt. The thrust zone has an unexpected thickness and, thus, hasn’t been penetrated completely. This is a pity, but the recovered material is unique and has a huge potential for subsequent detailed research by the COSC science team. A drill hole in such good rock seems to be ideal for the up-coming downhole studies of the geophysics and geothermal working groups (although we know that anything can happen to a drill hole). Continue to follow this page at least in the coming month to learn more about their research. Those researchers whose research is based (at least partly) on water conducting fractures and porosity, i.e. the hydrogeologists and microbiologists, were less lucky. We have seen very little of it. But who knows, maybe there are other interesting aspects in or despite it. And finally a unscientific conclusion, based on statistically not confirmed material: As soon as a microbiologists enters the drill site, the drill rig will most likely break down, or there will be another reason why drilling has to be stopped. No offence meant - we really enjoyed their company during the waiting time! And we sampled for them until the very last core run (core with water-conducting, calcite filled fractures!). And the show must go on … What’s next? The driller’s are presently pulling out the drill strings in preparation for the downhole measurements. The “leftovers” of the on-site science team close down the facilities, pack boxes, 2400 m of drill core have to be shipped, etc. etc. etc. During the autumn, we have to compile the data that were acquired during the operations, write an operational report, prepare the sampling party for the COSC science team … amongst others. In other words: It’s not that we don’t know what to do with our lives now