Classification and Function Of Oil Casing Pipe

Oil casing is abbreviated as casing, which is a kind of oil country tubular goods(OCTG). OCTG includes finished oil casing, oil tubing drill pipe, drill collar, coupling, sucker rod, and pup joint. Today, we are going to talk about classification and function of oil casing pipe.

Drilling Guide Bush:

Primarily employed in oceanic and desert drilling operations, the drilling guide bush serves the crucial function of separating seawater and sand to facilitate smooth drilling. The primary specifications for this casing layer are ∮762mm (30in) × 25.4mm and ∮762mm (30in) × 19.06mm.

Surface Casing:

Designed for initial drilling, the surface casing is utilized to drill through soft ground layers down to the bedrock. This casing serves to prevent the collapse of the formation and requires sealing. The main specifications for surface casing include 508mm (20in), 406.4mm (16in), 339.73mm (13-3/8in), 273.05mm (10-3/4in), and 244.48mm (9-5/9in). The depth of the downpipe depends on the soft formation's depth, typically ranging from 80 to 1500m. It experiences relatively low external and internal pressure, typically using K55 or N80 steel grades.

Technical Casing:

Employed in drilling complex formations, technical casing becomes essential when encountering challenging layers like collapse, oil, gas, water, loss, and salt-gypsum layers. Failure to seal these layers with technical casing can impede drilling progress. In deep and complex wells, multiple layers of technical casing may be necessary, requiring high mechanical properties and sealing performance. Steel grades commonly used include N80 and P110, and in deeper wells, non-API steel grades such as Q125 or even V150 might be employed. The primary specifications for technical casing include 339.73mm (13-3/8in), 273.05mm (10-3/4in), 244.48mm (9-5/8in), 219.08mm (8-5/8in), 193.68mm (7-5/8in), and 177.8mm (7in).

Oil Layer Casing:

When drilling reaches the target layer, typically an oil and gas-bearing horizon, the oil layer casing is utilized to seal both the oil and gas layer and the overlying exposed strata. Among various casings, reservoir casing attains the deepest downhole depth and demands the highest mechanical and sealing performance. Steel grades commonly used include K55, N80, P110, Q125, V150, etc. The main specifications for oil layer casing encompass 177.8mm (7in), 168.28mm (6-5/8in), 139.7mm (5-1/2in), 127mm (5in), and 114.3mm (4-1/2in), among others.