Types of Drilling Casing

1. **Column Casing**: This is the largest casing used in drilling operations. It is typically run into place before drilling begins to provide initial support for the wellbore and to prevent cave-ins. Column casing is often made of thick wall pipe to withstand the immense pressure from the earth's crust and the weight of the drilling fluids.

2. **Intermediate Casing**: Once the column casing is in place, intermediate casing is run to protect the column casing from the pressure of the hydrocarbons and to maintain wellbore stability. Intermediate casing is usually smaller in diameter than the column casing but larger than the production casing.

3. ** Production Casing**: This casing is run after the well has been drilled and completed. Its primary function is to protect the wellbore from collapse and to provide a conduit for production of oil or gas. Production casing is often perforated at specific intervals to allow for the flow of hydrocarbons to the surface.

4. **Surface Casing**: Surface casing is the first casing string that is run into the ground and it typically extends from the surface to a depth of a few hundred feet. Its purpose is to isolate freshwater aquifers and other shallow formations from the rest of the wellbore to prevent environmental contamination and to maintain wellbore pressure.

5. **Lock Casing**: This is a type of casing that is used in situations where the wellbore is subject to high pressure and high temperature conditions. It is designed to prevent the casing from expanding due to the temperature changes and pressure increases down the well.

6. **Drill Pipe**: While not technically casing, drill pipe is a critical component of the drilling string that is used to transmit rotary motion from the surface to the drill bit. It is usually made of seamless steel tubes and is connected together with threads to form the drill string.

7. **Casing Hangers**: These are devices used to hang casing strings in the wellbore. They are attached to the casing and then suspended from the drill string or production string above. Casing hangers provide a means of support and connection for the casing strings.