During oilfield development, special water injection Wells are used to inject water to the surface to maintain or restore reservoir pressure, giving the reservoir a strong driving force and increasing production rate and recovery.  There is a set of control equipment at the wellhead of injection well, whose function is to hang the wellhead pipe string, seal the annulus, and control water injection and well washing methods such as positive injection, negative injection, combined injection, positive washing and backwashing.

• Water injection Wells are divided into stratified water injection Wells and general water injection Wells according to their functions.
• According to the string structure, injection Wells can be divided into support type and suspension type.
• According to casing and well conditions, injection Wells can be divided into large cased Wells, common Wells and small diameter Wells.