What is the minimum well size that an air-powered pump will fit in?

The minimum diameter of piping or casing that is typically used for an air-powered pump is 50 mm for a 2-inch pipe. In the U.S. most vertical gas wells tend to be either 6-inch/150 mm pipe or 8-inch/roughly 200 mm pipe. So, pretty much all air-powered, electric, and piston pumps can fit within those 150 mm to 200 mm radius casings, but the minimum size is 100 mm.