On: 'No-water' hydropower turns England's hills into g...

[jaclaz]

It could be something like bentonite/baryte or similar drlling muds:

https://en.wikipedia.org/wiki/Drilling_mud

[pfdietz → jaclaz]

Drilling mud, however, needs to be at least somewhat viscous, so it will carry rock fragments from the drilling back to the surface.

[jaclaz → pfdietz]

Sure, but it depends also on the kind of drilling and of the terrain that is drilled, drilling mud is used also when drilling with buckets large holes, in those cases the use is only that of avoiding the collapse of the walls of the bore.

The generic idea behind these supposedly high efficiency reservoirs is to have something that is at the same time liquid enough and much heavier than water, most probably the actual formulation will be a compromise.