Running the casing

A casing guide shoe is attached to one end of one joint of the casing. The joint of casing is the brought to the rig floor and is suspended from the hoisting system in the derrick., with the guide shoe on the lower end. The guide shoe will allow the casing to be lowered in unconsolidated formations where there will be ledges in the well. The guide shoe will guide the casing past these ledges, to keep it from hanging up. The guide shoe also protects the end of the casing from damage while it is being run into the wellbore. The first joint of casing is now run into the wellbore and a float collar is attached to the top of that joint. Within this float collar is a one-way check valve. This valve prevents flow from occurring up through the inside of the casing, but permits flow down through the casing.
Once the float collar has been connected, joints of the casing are addad as the casing is lowered into the wellbore. The inside of the casing is filled with drilling mud to prevent the casing from floating out of the well due to buoyancy. During the running of the casing, centralizes and scratchers are placed at pre-determined intervals along the outside of the casing string. The functions of these centralizes are to centralize the casing in the center of the wellbore. Scratchers have spring steel teeth, which scratch through the bentonite the bentonite wall cake on the wall of the wellbore, to provide a better cement bond with the rock formations.