The development and improvement of Coiled tubing

Introduction

Coiled tubing, also known as continuous tubing or CT, is one kind of tubing made of alloy steel with good flexibility. After the origin of 1940s and 1950s, continuous tubing already taken shape, but there was still a long way to go before large-scale practical application. 1970s and 1980s were important periods of exploration and innovation in coiled tubing technology, greatly improving the performance of coiled tubing and laying the foundation for the application technology of modern coiled tubing . Until the 1990s, continuous tubing technology and production matured.

Exploration and innovation in 1970s and 1980s

In the early 1970s, as the continuous tubing operation expanded to deep wells and wells with higher operational requirements, due to the low strength of the tubing and the large number of butt welds, the continuous tubing was unable to withstand the pressure and tensile loads during deep well operations, resulting in a significant increase in weld damage and well drop accidents. At the same time, mechanical failures occurred frequently during operations, resulting in a low success rate for continuous tubing operations The reputation for poor reliability and safety has accompanied the development of coiled tubing for many years.

From 1979 to 1978, two major manufacturers of coiled tubing in the United States made significant improvements to the manufacturing process of coiled tubing, increasing the length of the steel strip from 76.2 meters to 457.8 meters, reducing the number of welded joints by five sixths. After rolling and welding the steel strip into a tube, stress concentration was eliminated through heat treatment, which improved the performance of the coiled tubing. In 1978, it was developed to φ 31.75 mm (11/4 in) coiled tubing.

In the late 1970s and early 1980s, several American companies such as Bowen, Hydra Rig, and Otis Engineering made significant improvements to the design and maintenance procedures of coiled tubing operating machines, successfully improving the performance and reliability of surface construction equipment and significantly reducing equipment damage rates. Although improvements in ground equipment have increased the reliability of coiled tubing operations, the significant improvement lies in the introduction of new processing techniques and quality control technologies for coiled tubing.

The 1980s was a turning point in the continuous tubing process. In 1980, Southwestern Pipe Inc. in the United States first introduced high-strength low alloy steel with a yield strength of 482.58MPa for rolling continuous tubing. In 1983, Quality Tubing Inc. began using Japan’s 914.4m coil steel plate, reducing the butt weld of continuous tubing by half. In the late 1980s, the company improved the welding process of the pipe column and simplified the welding sequence of the pipe end. Firstly, the steel strip was connected to a long steel strip using oblique welding technology, and then rolled into a complete continuous pipe, thereby dispersing the welding influence zone and improving the fatigue strength and service life of the continuous oil pipe.

In 1985, a new type of injection head was successfully developed for controlling 2590.8m long φ The 19.05mm (3/4 in) coiled tubing is operated, and the injection head uses a large slotted drive wheel similar to the Brown injection head to pull the tubing for lifting and lowering operations. However, it uses a roller instead of an arc-shaped sprocket drive system, which is a significant improvement that facilitates the use of larger sized coiled tubing and the improvement of its operating capacity.

In the 1980s, the improvement of coiled tubing pipes and manufacturing processes, as well as equipment improvements, made the use of large-diameter coiled tubing possible, and coiled tubing technology entered a new field of operation. In the late 1980s, φ 38.1mm (11/2in) and φ 44.45mm (13/4in) coiled tubing successfully manufactured. In 1990, the first one φ 50.8mm (2in) coiled tubing is used in well completion.

Moving towards maturity in 1990s

In January 1992, φ 60.325 mm (23/8 in) coiled tubing was introduced in the autumn of 1992, the first one φ The 88.9 mm (31/2 in) coiled tubing was used as an oil pipeline in the Gulf of Mexico. In March 1993, it was tested in a North Slope exploratory well in Alaska φ 88.9 mm (31/2 in) coiled tubing, φ 114.3 mm (41/2 in) coiled tubing was developed in 1994. From 1992 to 1993, the number of coiled tubing operation units increased from 533 to 561, an increase of 5%. At the same time, the sales volume of coiled tubing increased by 21%.

1992 marks the 30th anniversary of the continuous tubing industry, marking the beginning of the maturity of continuous tubing technology, and its applications are constantly developing horizontally and in depth. With the emergence of downhole tools for continuous tubing operation, as a time-saving, cost-effective, safe and reliable advanced technology, continuous tubing operation has been widely used in the exploration and development technical services of oil fields worldwide.

With the advancement of research and technology in various fields, as well as the improvement of people’s understanding of coiled tubing, as a relatively novel oil and gas well operation method, the number of equipment and application scope are constantly increasing. According to the 1993 statistics of Schlumberger and Dowell, there were 533 sets of coiled tubing operation equipment in the world in 1992, including 245 sets in South America, 90 sets in Europe, 59 sets in North America, 54 sets in the Far East, 55 sets in the Middle East, and 30 sets in Africa. In 1993, it increased to 561 sets, an increase of approximately 5%. According to preliminary estimates, the sales volume of coiled tubing increased by 21% between 1992 and 1993.

Summarize

The 1990s can be said to be the era of mature coiled tubing operation technology. The improvement and improvement of process technology, especially the development of downhole tools for coiled tubing operations, have advantageously promoted the expansion of this technology to a wider range of application fields.

The technically reliable coiled tubing has the feature of operation with pressure, continuous lifting, small size, fast operation cycle, and low cost. It can be foreseen that it has broad application prospects of petroleum equipment in the 21st century.

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