What is a steel casing pipe used for?

Steel casing pipe is an essential structural component in oil and gas drilling, geological exploration, and construction projects.

Simply put, the fundamental purpose of steel casing is to reinforce and support the wellbore, forming a permanent or temporary barrier from the surface to the target depth, thereby ensuring safety, control, and efficiency throughout the entire operation.

Steel casing pipe can be thought of as providing a "framework" and "defense line" for the wellbore, specifically in the following aspects:

1. Preventing Wellbore Collapse
Problem: The formation is composed of rocks of varying hardness and stability. Once drilled through and without surrounding support, these rock formations (especially loose, fractured shale and sandstone) are prone to collapse into the wellbore.

Solution: Run steel casing and inject cement. A solid metal cylinder and cement sheath permanently support the wellbore wall, maintaining wellbore stability and patency.

2. Isolating Different Formations
This is one of the most critical functions of steel casing, acting like a "wall" within the wellbore.

Isolating high-pressure and low-pressure zones: Preventing high-pressure fluids (such as oil, gas, and water) from entering low-pressure zones, causing blowouts or contaminating producing strata.
Isolating unstable formations: Such as salt-gypsum layers and creeping rock formations, preventing them from squeezing the wellbore.
Isolating freshwater formations: Preventing drilling fluids, oil, gas, or hazardous fluids from contaminating underground drinking water sources – a paramount environmental and safety requirement.

3. Controlling Downhole Pressure and Preventing Blowouts
Steel casing and the blowout preventer (BOP) form the core well control barrier. Robust casing provides the foundation for installing the BOP and can withstand the high pressures generated during well shut-in, making it the last line of defense against catastrophic blowouts.

4. Providing a Pathway for Oil and Gas Production
The production casing forms the "highway" for oil and gas to flow from reservoirs thousands of meters deep to the surface. It protects the integrity and tightness of this pathway throughout the life of the oilfield, which can potentially last decades.

5. Foundation for Installing Other Equipment
All production equipment, including the casing head, Christmas tree, downhole pump, packer, and safety valve, are installed on top of or within the casing.

Classification by Use:

Types of Steel Casing:

1. Conductor: Prevents shallow surface soil from collapsing and establishes an initial path for drilling fluid to return to the surface.
Drilling Depth: 30-100 meters.

2. Surface Casing: Isolates freshwater formations to prevent contamination; responds to shallow gas surges; and supports the weight of subsequent, heavier casing.
Drilling Depth: Several hundred meters.

3. Intermediate Casing: Isolates complex formations (such as high-pressure zones, lost-hole formations, and salt-gypsum formations) to create safe conditions for continued drilling at deeper depths. This may involve more than one layer.
Drilling Depth: Several thousand meters.

4. Production Casing: The innermost, permanent barrier of the wellbore, used directly for oil and gas production. Highest requirements, requiring corrosion resistance, high-pressure resistance, and excellent sealing.
Depth: Downhole to the bottom of the well.

5. Liner: Functions similar to technical or production casing, but is suspended only at the bottom of the upper casing, offering a cost-saving solution.

Depth: Does not extend to the wellhead.

Read more: OCTG Casing Pipe Price & Cost or Seamless Casing vs. ERW Casing