Ann: Southern Cooper Basin Operations Update, page-80

Not much to tell... they are just pumps where you can adjust the number of pump strokes per minute.

I think all pumps used in CSG are variable speed. The two main types are PCP and ESP. Both of them are variable speed because they both rely on rotation of the pump, so you just increase the rotation speed to increase the pump rate.

PCP is normally used in Qld CSG but for deeper, hotter, high CO2, and high water flow situations, they usually use ESP. I suspect STX are using ESP (or maybe another type altogether) rather than PCP which is not really suitable here.

The theory behind using them slowly to prevent loss of permeability is to avoid lowering the pressure immediately around the wellbore to a level where elastic rebound occurs in the coals and closes up the cleats. It will still happen eventually when you drop the overall reservoir pressure down, but the aim is to delay it long enough to get some of the gas out first.