What is "well completion"?

A Well completion need a number of equipments/devices to joint in a series to form a Well completion string and run down in hole for oil production or oil recovery.

Those equipments sometime needed running tool / puuling tool to run, pulled or set the packer

(Equipment that like production permanent packer, lock mandrel, Sliding side door (SSD) and some other locking device that used in well.)

who are those Well completion companies?

company like:- smith international, Baker huge, Halliburton, Schlumberger, Weatherford and BJ services