1. Floating shoes and hoops
In the early stage of oilfield development, the support ring (choke ring), also known as float collar, was used to control the downward position of rubber plug during cement injection, so as to ensure the length of cement plug and prevent backflow of cement slurry. However, it relies on the sealing of metal and nylon, with poor sealing effect and low pressure bearing capacity, so it is gradually eliminated. Floating shoes or hoops are casing guide shoes or hoops that can produce buoyancy. Guide shoe is used to guide the casing string smoothly down the wellbore to the well, prevent the casing foot from inserting into the wall rock layer, and reduce the well running resistance.

Floating shoes have the function of leading shoes - circumfluence. Keep the drilling fluid flowing in the annulus during casing running. The float collar also has the function of preventing the backflow of cement slurry, at the same time, it also has the function of bumping the rubber plug during cementing, limiting the depth of artificial bottom hole and the height of cement plug at the bottom of the casing string, so as to ensure the sealing quality of the bottom of the casing. Due to the high temperature resistance, good sealing and drill ability of floating shoes or hoops, the connection is convenient, so it can replace guide shoes, casing shoes, etc.

Classification   

According to the different ways of drilling fluid entering into the well when casing is running, the float collar of float shoe can be divided into ordinary type and self filling type; according to the working mode of back pressure device, it can also be divided into float ball type tongue plate, etc. Floating hoop is used to receive rubber plug group, so that there is a section of cement plug between hoop shoes, and the impurities attached to the inner wall of casing can be contained, so as to ensure that the cement slurry column is not displaced, so as to ensure the cementing quality outside the casing shoes. At the same time, it can be used as a backup to prevent backflow of cement. The float collar is used to control the height of the cement plug in the casing string. It has buckles at both ends and can be connected between any two casings. The float shoe only has a female buckle at one end and can only be located at the front end of the casing.

The float collar and float shoe are of cement type and metal type. The float shoe is generally at the lowest end of the casing, while the float collar is generally at the upper end of the float shoe. A float collar will also be added during the two-stage cement injection. Its basic function is to prevent the cement slurry from returning during the cement injection.