www.drillingmanual.com/wells-... - A packer is a tool used in oil and gas production well, which when set, seals the annular space between 2 strings of pipe or a string of pipe and the open hole. They also must have the capability of permitting production flow through them and onto the surface. As its major functions, a packer should :
1- Protect casing from bursting under conditions of high production or injection pressures
2- Protect casing from corrosive fluids
3- Provide better well control
4- Prevent fluid movement between productive zones