What are OCTG pipes? Oil country tubular goods are pipes used for onshore and offshore oil & gas upstream operations (extract oil and gas from the wellbore). OCTG pipes may be classified into three main families: drill pipes (to perforate the soil and reach the reserve), casing pipes (to consolidate the well and prepare it for the actual extraction), and tubing pipes (to extract the product from the ground to the surface). API 5CT is the reference specification for OCTG pipes.
TYPES OF OCTG PIPE
First, OCTG is the acronym of “Oil Country Tubular Goods” – i.e. pipes for oil (and gas) extraction from the soil. The three main OCTG pipe types are:
- Casing pipes are used to stabilize the wellbore. A casing pipe is subject to axial tensions and to internal pressures generated by the pumped oil or gas, by their heavyweight and the external pressures coming from the surrounding rocks
- Tubing pipes are tubular goods through which the oil or gas is transported from the wellbore to the surface. Tubing segments are generally around 30′ long with a threaded connection on each end (standard or premium connections are available)
- Drill pipes are heavyweight seamless tubular that rotate the drill bit and circulates the drilling fluid. Pipe segments of 30′ are coupled with tool joints. Drill pipe is subject to high torque by drilling, axial tension by their weight, and internal pressure due to the purging of the drilling fluid. Additionally, alternating bending loads due to non-vertical or deflected drilling may be superimposed on these basic loading patterns
The API 5CT specification covers seamless and welded casing and tubing pipes for upstream operations (pipes that belong to the OCTG family, as illustrated above).
Let’s review each type of OCTG pipe more in detail.
OCTG “CASING” PIPES
OCTG casing pipes are a key structural component for an oil & gas well and have the following scope:
- Keep the borehole stability in the well
- Prevent the bore contamination from water sands
- Prevent water from producing formations
- Exercise a tight control of the wellbore pressures during the drilling, production, and repair operations
Casing pipes are used to install:
- Blowout Preventers (BOP)
- Other wellhead equipment necessary to extract hydrocarbons
- Production tubing and packers
Casing pipes are also one major individual component of the overall cost of the well, therefore the correct selection of the casing size, materials, connectors, and depth shall be at the top of design engineers (for cost and efficiency reasons).
The six basic types of casing strings are:
- Conductor Casing
- Surface Casing
- Intermediate Casing
- Production Casing
- Liner tieback casing
Oilfield casing pipes are positioned into the wellbore and cemented in place to secure both subsurface formations and the wellbore from collapsing