I just saw the news that the “top kill” method to stop Gulf of Mexico oil well leak has failed. I tweeted yesterday that I thought it had the same chance of success of using Blu-Tack (or chewing gum) to fix a radiator leak. While it might stem the flow for a little while, inevitable the fluid under pressure is going to find fissures and capillaries to follow and eventually hydraulicly lift the intended seal away from the surface. However, I feel all is not lost.
I regularly need to get anchorage on difficult surfaces. I am talking about mounting shelves on plasterboard (drywall) or bolting brackets to brick or concrete. To do this you can use various proprietary wall anchors. Almost all of these use some sort expanding material (plastic or metal) such that when a screw or bolt is turned, the device expands outwards into the wall. This is using basic mechanical principles of an inclined plane and/or lever. The screw of course is a inclined plane wrapped around a cylinder, and often there is two others working as wedges that expand, or some use levers in an umbrella like fashion to expand. The anchor is held fast through shear friction against the wall you are attaching to.
You can also create an expanding surface using fluid pressure. This is done in a clinical stent that is used to temporarily or permanently hold arteries or other ducts open. Some use a balloon that expands up air pressure, or some are mechanical similar to a wall anchor.
Another example is the sanding band I have for my rotary tool. It uses a screw to expand a rubber grip, which holds on to the band.
Either way, I don’t see why such a device, suitably encompassed by say a rubber sheath, could not be inserted in the well, expanded to hold fast on the wall, and the sheath would stem much of the leak. Even if it isn’t a total seal, I imagine you could gaurantee the porosity could be well less than 10mm or so. You could then pump “mud” or what have you through this anchor, into the well to stem the flow further. This stent/wall anchor would push against the sides and rely on pressure to hold it in. It could be driven either via hydraulic motors or rams to create the necessary leverage, akin to me turning the screw on my wall anchor. (A balloon stent mechanism might also work but there maybe issues of expanding a balloon 1500m below the sea).
I imagine the well bore is lined with a metal casing. There is of course a risk that the whole casing might be pulled out as the gas/oil pressure pushes against the wall anchor or seal. But I guess there is nothing stopping you inserting another anchor, if it is blown out, which can be driven against the natural earth wall left once the casing is removed. (You could even have a mechanism to drive horizontal spikes out of the anchor to get a more positive grip).
Yes there are obvious issues of working robotically at such pressures. Also the stent/wall anchor needs to be designed and built and tested to work under the needed forces. I’m not sure the state of the top of the well now, but clearly any valves or the like need to be removed, to leave a clean hole to insert the anchor/seal. My sketch below shows the 4 steps needed.
I have added a more deailed diagram below showing how the stent/anchor would operate. The hydraulic motor would drive the shaft. It would be threaded with left and right-hand threads. This way a rotation of the shaft would drive the nuts towards each other in pairs. (This is the same as how turnbuckles operate). The lever and hinge arrangement connected to the nut pairs would cause expansion of the sheath sealing the shaft. The head of the device might be complete sealed. The shaft could also be hollow to allow pumping of mud to properly seal the well.