This string is used in thermal recovery wells. When the injection operation is changed to production or vice versa, it   is unnecessary to kill the well. So the pollution and cold formation damage caused by killing fluid can be avoided.   The key tools are hanging packer, underground switch and plug-in sealer.

◎ The sealing is reliable both for injection under high temperature and tripping in under low – medium temperature;

◎ Unnecessary to kill the well when changing the string, avoiding formation pollution;

◎ Double sealing;

◎ Pin lunge is used to change the switcher, easy to judge on or off situation.