Octg Tubing Classifications and Application in Oil Well Project

OCTG tubing is divided into external-upset tubing (EU), non-upset tubing (NU) and integral-joint tubing. EU tubing is referred to the pipe end without direct threading and wear a collar; NU tubing refers to two pipe end upset through external upset then threading again and bring the collar; Integral-joint tubing refers to the pipe end through thickening outside the tubing connector, the other end through external upset interior thread, connected without collar directly.

API 5CT included an illustration on API 5CT tubing joint connectors. When casing is used as tubing, long-thread coupling or short thread coupling and buttress-thread coupling connections can be specified.

The EU tubing coupling is widely applied in the project because it has good and serviceable connection in many oil wells. The EU joints, designed joint strength in tension and pressure strength, are greater than the pipe body, thereby, the EU joint is considered a 100% joint efficient connection. In addition, the joint requires good thread compound as outlined in API RP 5A3 for proper lubrication and sealing. To improve the sealing performance of EU tubing in high-pressure service and a grooved coupling, which accepts nonmetallic seal rings, is used in the coupling sometimes. To offer more clearance, API special clearance EU couplings are available. Besides, The OD sizes of API EU joints range from 1.050 to 4.500 inches.

The NU tubing is less than EU tubing in application. The NU tubing cost is slightly less than EU tubing and the joint strength is substantially less. The sizes of API NU joints are available between 1.050 and 4.500 inches. And the coupling joint diameter is less than EU joints.

API Integral joint tubing has a 10-round form with a joint strength which is less than the body minimum yield, which restricts its use. The OD sizes of integral joint tubing are available of 1.315 to 2.063 inches. The little OD of integral joint tubing permits its use inside larger tubing strings or in wells as unloading or vent strings. The couplings should meet all the minimum requirements in API SPEC 5CT specifications. API SPEC 5B3 and API RP 5B14 cover threading, gauging and thread inspection.

1. Oil extraction steam: finish oil and gas well and cementing, place API 5CT tubing in the oil layer to extract oil and gas to the ground;
2. Water injection: when the down hole pressure is not enough, through OCTG tubing to water injection into the well;
3. Steam injection: use insulated tubing to the down hole steam input in the processes of heavy oil thermal recovery.
4. Acidification and fracturing: in the late drilling or to improve the yield of oil and gas wells, oil and gas layer need to enter medium curing of acidification and fracturing. The medium and curing are conveyed by oil tube.