Are QED pumps susceptible to the introduction of fines? If so, what is the remedy for returning them to pumping efficiently?

Actually, all pumps are susceptible to accumulation of fines, such as silts or other solids. The rate at which fines accumulate, especially in gas wells, is dependent on the well construction. If you use a finer rock backfill or even a gravel backfill you can reduce some of the fines that way. At some sites, in the last 3-6 meters/10-20 feet of depth you can actually use coarse sand as opposed to rock. The purpose of that is to keep fines out of the wells as liquid is being pumped but still have the ability to pull gas. If fines accumulate to the point that you get fines inside the pumps themselves it can, in fact, reduce the pump output or shut it off completely. Because QED pumps have large clearance passages you can usually just pull them up and clean them on-site.  Cleaning can be as simple as washing the pump with a surfactant or detergent solution in water.  It may require some cleaning inside the pipe to break down any accumulated solids that are deposited, but typically the pumps can be cleaned in the field and put immediately back into service.  You could have a spare pump or two, so in those situations where the pumps clog up due to fines you can pull the pump and replace it with the spare, leaving you time to take the clogged pump out of the field to clean it.