Sanded-up wells

I have heard of oil wells becoming "sanded-up" and the companies having to use a work-

over rig to clean them out. I have also heard of using a "sand basket" to assist in the

removal of the sand. Can anyone tell me how this system works? Also what does sanding-

up mean and once cleared of sand, will this process prevent this from occurring again in

the near future? Thanks for any reply.

w r gordon