Day 12: If you love something, set it free; if it returns, it is yours; if it gets stuck in a borehole, pull harder


July 10, 2011; 10:52 PDT
July 10, 2011; 17:52 UTC

47 45.474300 N
127 45.753900 W

When I last posted on the 7th, the wind had put operations on hold. The next day, the wind had died away, leaving the water as still as a lake. At 8, local time, we launched Jason and Medea again. I’m not sure if I properly explained the arrangement yet, but Jason is a neutrally buoyant remotely operated vehicle, which neither sinks nor floats, but can maneuver with propellers. Its attached to the ship through a long tether that supplies power and data both ways. The ship maintains a position directly above Jason, however the ship always moving a few feet one way or another, and with a mile and a half of cable between them that motion could tug Jason one way or another each time the ship rose and fell with the waves. If it ever went taught, it would be under tremendous strain, too. Instead, the tether connects to Madea. Half ROV, half giant plumb, Madea hangs at the end of a taught line that gets swung and dragged with the motion of the boat, and Jason connects to Madea through a second tether 60 m long (around 100 feet).

The first dive on the 8th, dive J2-569 (the 569th dive on the second generation Jason ROV) attached a set of osmo samplers to wellhead 1352A (sorry, I don’t know how they name wellheads). There are several ways to package equipment like osmo samplers. These were boxed into milkcrates with feed lines that get plugged into outlet ports on the wellhead. Next, Jason moved to wellhead 1362B to download flow measurements, collect fluid in inflatable bags, and attach more crated osmo samplers. Unlike 1352A, 1362B has an orifice about 4 inches in diameter that continually vents hydrothermal fluid. This orifice has flow meters that measure the rate of flow out, and if we were to tap lines into ports like we did with 1352, we would divert some of the flow away from the flow meter. Instead, we attached an umbilical line that sipped water from the opening and fed it into the osmo samplers.

The next day was July 9th, yesterday as of the time of writing this. While the Jason team began dive J2-570, Gus and I set about cutting recovered osmo sampler tubing. The osmo samplers draw water into long thin tubes at a slow, continuous rate. This means that when they are recovered, they provide a history of the water moving into the sampler over the duration of the deployment. By cutting them into meter-long segments and then draining the contents of those segments into tubes, we can analyze each tube as a sample of water characterizing a specific range of time. It was repetitive work, but we listened to music and the time went quickly. Afterwards, I went to watch the dive progress on the monitor in the lab. We had returned to wellhead 1027C. This was the first wellhead we visited on the cruise, where a damaged cap was preventing us from accessing and replacing equipment inside the well. The cap had attached itself to the wellhead, and on a previous cruise the handle had broken off while trying to break it free. We had returned with a cleat that slid into grooves on the cap (known as the top hat), which gave purchase to a screw that would apply tremendous upward pressure as it was turned. The screw, called the Top Hat Extraction Tool, or THET, had done its job, lifting the top hat about 6 inches. It was assumed that the cap would come away readily once its seal was broken, but it appeared it had become stuck to the equipment beneath it, and 400-600 pounds of lift by the Jason ROV was not enough to lift it. Finally, we had returned to execute plan C. A bridle had been made that attached to the THET to Madea. Unlike Jason, which ascended by propelling itself toward the surface, Madea has no vertical mobility. She simply hangs heavily at the end of her massive cable. When a dive ends, a winch hauls all 2.6 km of cable up to the surface. With the bridle in place, all the power of this winch was firmly attached to the stubborn equipment.

Systems were go. I asked the operator, afterwards. When I was watching the top hat and data logger withdraw from the well, the cable was under 7900 lbs of tension. Madea puts about 7000 lbs on the cable alone, and the damaged gear weighed about 200 lbs, meaning that the force needed to dislodge the stuck items was about 700 lbs. On our previous try, we’d been a few hundred pounds of force short, but if at first you don’t succeed, apparently you just need to pull harder. The wellhead is now clear, and ready for refitting once the new gear is ready for deployment.


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