The picture above shows a cutting shoe for an Extended Core Barrel (XCB) drill bit. On this expedition, we have alternated between 3 types of drill bits. The XCB, Advanced Piston Coring (APC) and Rotary Core Barrel (RCB). Each bit and cutting shoe is best suited to a certain kind of sediment and set of drilling conditions. The APC is best for soft sediments and is usually used at the beginning of the hole. When things get too firm for the APC to work well, we swtich to XCB, which is best for firm sediments. When we drill deep enough to hit lithified sediments (actual rock), then we bring in the RCB. By switching bits back and forth to match the conditions, we are able to get the best possible recovery for the setting.
The drilling operations go on 24 hours a day, 7 days a week during the expedition. Bits and cutting shoes are replaced as they show signs of wear or damage from the heat and friction of drilling. Just to give you an idea of how hard this equipment works, here are some numbers for this expedition so far.
As of today, we have drilled 8 holes. Those 8 holes yielded a total of 498 cores. Those 498 cores are broken down into a total of 1986 sections averaging one and a half meters in length. When you add all the holes together, the drills have penetrated a total of about 4650 meters into the sea floor (combined). We have retrieved over 2000 meters of core. Out of that 2000 meters of core, over 25,000 individual samples have been collected. Some for shipboard analysis, but the majority for post cruise research back on land.
Hopefully this gives you an idea of the frenzy of activity that is going on during drilling operations. Right now the ship is quiet – we are drilling a dedicated hole for logging (with no core retrieval), and the scientists are all working on writing their reports. In a few days we’ll be at site #4, adding more cores to these already impressive numbers. Then before you know it, we’ll be back in port. I can’t believe this expedition is drawing to a close so quickly! I’ve learned how much more there is to this work than just “digging a hole”!