Coiled tubing initially gained a foothold in the market as a cost-effective wellbore cleanup tool. The economic income from well workover and completion operations accounts for more than 75% of the total income from coiled tubing operations, and the scope of application of coiled tubing in oil and gas fields around the world continues to expand. The advantages and application value of coiled tubing such as under-pressure and underbalanced operation, fast and efficient operation, low damage to the formation, low cost (from the simplification of the process), etc., are the most popular features of coiled tubing 30 years after its birth. It was only really recognized by people in the 1990s. Since then, coiled tubing has been widely used in oil and gas field workover, drilling, completion, logging, and other operations, playing an increasingly important role in oil and gas field exploration and development.
After the 1990s, coiled tubing fracturing technology and coiled tubing drilling technology have developed rapidly in process technology and practical applications. The introduction and utilization of coiled tubing operating technology in my country began in the 1970s. In 1977, my country introduced the coiled tubing operating machine produced in China and began to use coiled tubing in the Sichuan Oilfield for small-scale acidification of gas wells, and nitrogen injection to remove residual acid and gas lift. For some simple operations such as liquid reduction, sand washing, wax removal, drilling, and grinding, application tests have been carried out in hundreds of wells, and obvious results have been achieved. Preliminary experience has been accumulated and subsequently promoted and applied in various oil fields.
According to incomplete statistics, there are about 30 coiled tubing operating machines introduced in China, mainly distributed in Sichuan, Daqing, Changqing, Shengli, North China, Central Plains, Jilin, Xinjiang, Liaohe, Tuha, Dagang, Henan, and Karamay oil fields. Since the introduction of coiled tubing in Sichuan, Liaohe, and North China, the cumulative number of well operations has exceeded 1,000. Since the Daqing Oilfield introduced coiled tubing operation equipment in 1985, it has carried out various downhole operations such as well workovers in more than a hundred wells. It is mainly used for gas lifting, wax removal, well cleaning, sand flushing, cement squeeze plugging, and cement drilling. Sai et al. Since the introduction of coiled tubing operating machines in Tuha Oilfield in 1993, the number of wells operated has reached 40 to 60 times, and the well depth recorded with coiled tubing has reached 4,300m.
Generally speaking, domestic coiled tubing operating machines are mainly used in the following aspects: sand washing and well cleaning, drilling bridge plugs, gas lift, liquid nitrogen injection, wax removal, liquid drainage, acid squeezing, and coordination testing. The most commonly used ones are sand flushing, gas lift drainage, and wax removal, accounting for more than 95%. Coiled tubing operations are generally welcomed in my country's oil fields.
