Kill and Kill Again

August 8, 2010

NOAA Ship Henry Bigelow at the wellhead

The NOAA Ship Bigelow entering the wellhead area to conduct an acoustic survey over the wellhead. Picture taken from DDIII, the rig drilling the relief well.

The days during and after the “kill” operation have been busy. During the operation we were not granted access to the wellhead region. The last thing anyone needed was another ship working through the area, distracting from the operation itself. We patiently circled outside the 1500 m looking for acoustic evidence of material escaping the wellhead region at depth and visual evidence of oil on the surface. We saw no acoustic evidence at depth, but the data were sent to acoustic experts on shore for more thorough analysis.

We did observe some oil on the surface: 1 to 2 foot diameter areas of sheen, one larger patch and numerous little whisps. Some of this was likely from all the ships operating in the area, but some may have been from the wellhead. Our efforts to collect these little spots were largely unsuccessful.
We used this time to prepare for water sampling. Our water sampler is twelve 5 liter bottles that go into the ocean all open on a carousel. The sampler is lowered to depth and then raised. Bottles are then closed at certain depths. Our problem was that sometimes the bottles would not close.

The electronic control from the ship goes through a number of steps before reaching the carousel to close the bottles. The computer running the whole operation is in a lab on the ship. This computer is connected to a deck box that contains the “brains” of the water sampler and other equipment on the carousel. The deck box is connected to slip rings on the winch, and through these slips rings to the wire used for lowering the carousel. The winch has a large drum with wire wrapped on it. To lower the equipment, the drum spins paying out wire. The slip rings allow for the electrical connection to be maintained between the deck box and the wire while the drum turns – one of many ingenious technical solutions that makes sampling the ocean possible.

The wire has the electrical wires inside and the weight bearing part outside. Think of it as normal wire, with copper inside and insulation outside. But in addition to insulation there is another layer of wire that hold thousands of pounds of weight. At the end of the deployment wire there is another ingenious solution to a problem – how to get the inner electrical wire out from the center of the weight-bearing wire while preserving both the electrical connection and the weight-holding capability of the outer wire.

The poured termination is the solution. The whole wire is passed through a steel fitting and the electrical wires are taken to the next step. Metal is then liquefied and poured into the fitting. Once the metal solidifies in the fitting you have a weight-bearing termination with the electrical wires coming out. These wires are then connected to the wires that connect to the carousel. This splice of wires is also special because it must be waterproof even at the extreme pressures of 1000’s of meter (see for more information).

Somewhere in this electrical chain, we had a problem; it wasn’t that the carousel didn’t work; it worked most of the time, but not all of the time. Intermittent problems are the hardest to troubleshoot.

We changed everything we could see, with no luck. However, we found that if we turned the deck box off and then on again, everything would work for a while – usually long enough to collect all the water samples we wanted. The problem wasn’ fixed, but we had a work around.

We heard reports that the “kill” operation was for “all intents and purposes was successful.” We didn’t quite know what this meant, but soon after we were granted access to survey over the wellhead. Over the next three days we made more than 25 passes with our acoustic instruments. Although the acoustic signatures over the wellhead appeared lower, there was much more background noise. This noise made preliminary assessments difficult. We transferred data ashore for more thorough analysis.

We also were given the opportunity to start water sampling under the conditions that we could return to the wellhead on short notice. Working with our shore-side support, we decided to sample a set of stations 2.5, 5 and 10 km from the wellhead. With our water sampling carousel mostly working we started making casts.

Jon Hare
Chief scientist

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