What is thickened casing pipe?

What is thickened tubing and casing?
External Upset End Tubing (EU or EUE) is a special tubing designed for oil and gas well exploitation in the petroleum industry. The pipe walls at both ends are specially thickened before processing threads and assembling couplings. It has stronger mechanical properties and connection reliability than ordinary flat tubing (NU). In the field of oil pipes, tubing is mainly divided into three categories: flat tubing (NU), thickened tubing (EU) and integral joint tubing (IJ). Among them, thickened tubing has been widely used in deep wells, high-pressure wells and complex working conditions due to its unique structural advantages and performance characteristics.

From a historical development perspective, thickened tubing technology has gradually developed and matured as the oil and gas exploitation environment becomes increasingly complex. In the early days, oil field development was mostly concentrated on shallow oil and gas resources, and ordinary flat tubing could meet production needs. However, as the development depth increases, downhole pressure, temperature and corrosive media have put forward higher requirements for tubing, prompting the emergence of tubing end thickening technology. The thickening treatment effectively solves the structural weakness of the threaded connection part and significantly improves the overall strength and sealing performance of the tubing system. According to the API standard, the outer diameter of the thickened tubing usually ranges from 42.13mm to 114.3mm (1.66 inches to 4-1/2 inches), and the wall thickness ranges from 3.56mm to 16mm, which can meet the technical requirements of different well conditions.

The core feature of the thickened tubing is its end thickening design. Unlike the flat tubing, which directly processes the threads on the pipe ends, the thickened tubing first heats and applies pressure to increase the wall thickness of the pipe ends during the production process to form a thickened section with a smooth transition, and then the threads are processed. This design significantly increases the cross-sectional area of the threaded connection part, thereby improving the tensile strength and anti-extrusion capacity of the connection. According to the different thickening forms, thickened tubing can be divided into three types: external thickening (EUE), internal thickening (IUE) and internal and external thickening. Among them, external thickening tubing is the most common. Because of its relatively simple processing technology and superior performance, it has become the mainstream product in the industry.

From the perspective of functional positioning, thickened tubing has multiple missions in oil and gas wells: first, it serves as a channel for oil and gas to flow from the bottom of the well to the ground; second, it serves as a downward channel for injection media in water injection development; third, it serves as a conduit for steam injection in heavy oil thermal recovery; and fourth, it serves as a pipeline for high-pressure fluid in acid fracturing operations. These functions require that the tubing must have sufficient strength, sealing and durability, and thickened tubing meets these stringent requirements through its special end reinforcement design, becoming an indispensable key equipment for modern oil and gas production.

It is worth mentioning that although the manufacturing cost of thickened tubing is higher than that of flat tubing, the long-term economic benefits it brings are very significant. Taking an oil field in Bohai as an example, the misuse of flat tubing instead of thickened tubing caused the wellhead seal to fail and caused a blowout, with direct economic losses exceeding 280 million yuan. This painful lesson fully proves the importance of correctly selecting thickened tubing, and also reflects the key role of thickened tubing in ensuring the safe production of oil and gas wells. As my country's oil and gas resource development continues to expand into deep layers, deep sea and unconventional areas, the technical status and application prospects of thickened oil pipes will surely be further enhanced.

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