At Sea Report from the Bismarck Sea: Trying to drill a hole
December 4th, 2000
After pulling out of Hole 1188B we decided to go back with a new type of diamond bit called the Advanced Diamond Core Barrel (ADCB) to try to deepen the hole beyond 72 mbsf. The attempts were not successful because there were 12 m of fill at the bottom and this bit was designed to cut rock and not to clean out rubble. We pulled out of the hole and decided to attempt to drill a deep hole by stabilizing the upper 200 m with casing (cylindrical metal case that is put in the hole and cemented in place to prevent the hole from caving in). This would require a re-entry cone and a hole of about 200 m in depth. The drilling and casing operations meant that the hole was going to be drilled with an oversize bit (14.75" compared to the regular 9.875" size) and there would be no core available during this time. Preparations were going to take place on the order of 24 hours before we were ready (welding the re-entry cone together, testing equipment, and putting together the bottom hole assembly) so before we committed to drilling a deep hole, we decided to drill a shallow hole in an area called Satanic Mills. This shallow hole would provide some core for the scientist to analyze and added information from a nearby area.
Drilling went along fine and at approximately 14 mbsf we decided to deploy thermometers to get an estimate of the temperature conditions in the area. We could not have picked a worse time to do this because the hard formation finally got the best of our equipment once again. After reaching 20 mbsf, we sheared of the bit and the core barrel, along with our tool on top of it, went along for the ride. I ended up losing my first tool and I was not too happy about it.
After that unfortunate episode, we came back to our first (Site 1188 - Snow Cap) to begin our quest for a deep hole. The deepest penetration in the first three attempts (Holes 188C, D, and E) was 44 mbsf. In our 4th attempt we drilled to 200 mbsf, deployed a re-entry cone, and we are now in the process of trying to put our first casing string to a depth of 60 m. If all works out, we will add an additional casing string to 180 m and hopefully this will allow us to core to a depth of 500 m or deeper and then do some logging. Wish us luck!
We are now processing the RAB images from the logging-while-drilling hole (Hole 1188B) at the Snowcap diffuse venting site. These images show promising evidence of structures and stratigraphic units not observed in the recovered rocks due to the poor core recovery in the upper part sections in this area (~ 6.5%).
We have also been keeping and eye on the impressive eruption plume from the Tavurvur volcano at Rabaul, 82 km to the southeast of our current position. A message from the Rabaul Volcano Observatory has indicated that even though there has been some ash clouds developing in the last few days, there has been no real change in the volcanic activity. The recent regional earthquakes did not seem to have affected Tavurvur. Their earlier reports also indicated that some coastlines were affected by high water surges after the earthquakes on November 16th, 2000. The main coast of mainland Bougainville was one of those coastlines but there have been no other reports after that. Earthquake activity is occurring along segments of the Weitin fault but the numbers and magnitudes are on the decline.
On the more social front, our Sunday BBQs have been moved to 6 PM local time because the heat made them more like a sauna at their more commonly scheduled time at noon. We also had our 3rd boat and man overboard drill last Tuesday. It was unusual because they actually put the Zodiac in the water and the 2nd mate along a crew member went for a ride with everybody else looking at them with eyes full of jealousy. A couple of the scientist asked the Captain if they could go for a ride and he let anyone that wanted to go could do so as long as they were wearing shoes (I know is a strange concept but remember that is hot out here and many of us wear sandals most of the time), a life jacket and a hard hat. A long line formed right after that and there were many joy rides during the afternoon.
This is it for now and lets see what happens next week. At least I hope that the weather improves because it has been rainy for about a week or so.
Gerry
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