Speaking of comments, there was one, from Murray earlier in the week about someone who had drilled a series of dry holes, in an area where earlier drilling had been successful. When he tried to find out why, he discovered that his holes had been drilled with mud, while the earlier holes had been drilled without mud. As I mentioned in the mud piece, one of the objects of having mud in the fluid that is circulated through the well during drilling, is to coat the walls of the hole, so that fluid doesn't escape into the surrounding rock. The down-side to that, of course, is that the mud coats the walls of the rock that has the oil in it, so that the oil can't get out.

One of the ways this can be removed, is basically the same as if your house, or car was covered in mud. On the surface you would just take a pressure washer, and wash off the mud. This works better than a scrubbing brush would, down-hole, since the rock has also been crushed a little at the edges by the action of the drilling bit as it passed. The combination of crushed rock and mud gets into the thin cracks that provide the rock permeability, and a simple mechanical scrubbing can't easily reach into those narrow passages. A high pressure jet of water, however, can and will wash all the debris from the walls of the hole, opening the rock up to its original permeability.

However, (aren't you beginning to hate that word) there is a snag.