The Calculation And Analysis Of The Drill Torque In Coiled Tubing Sidetracking Window

With more and more oil and gas fields having been entering the late stage of development in the world, they encounter some similar problems in oil and gas production. Oil production dropped significantly, serious flooding, casing damage, complex reservoir structure and drilling accidents are hindering the exploitation of oil. In our country, the number of abandoned wells is increasing year by year. It’s also increasing the cost of oil and gas exploration. Many abandoned wells also have high mining value. If we can effectively reuse these wells, it will largely help relieve our resource constraints and it’s conducive to economic progress.At present, various problems about oil and gas production have been resolved in casing sidetracking technology. This technology is not only used in well completion and well workover, but also makes many abandoned wells reusable. In 1990s, coiled tubing sidetracking technology, which was widely used in drilling and completion, has turned more and more popular. CT is an equal long bent pipe without joints. It can carry high pressure and it is convenient to transport. It can rise and fall continuously and it’s utilized in dynamic packing well. Coiled tubing sidetracking technology is more effective than conventional technology. Its under-balanced pressure drilling system could reduce damage to the oil layer. Its drilling fluid circulation system could obviously reduce trip. To some extent, it increases drilling safety. It is useful to achieve automatic control and MWD by built-in cable in the coiled tubing. It is highly suitable to drill a slim hole and to sidetrack in old well. Coiled tubing sidetracking technology includes cement plug sidetracking technology, cement sheath built-in whipstock sidetracking technology, whipstock sidetracking technology and abrasive fluid jet sidetracking technology. This paper focuses on the research of whipstock sidetracking technology, which needs fewer times of tripping and has a higher utilization rate.In the process of coiled tubing sidetracking, the formation of borehole is the result of milling between the drill bit and casing as well as layer. This process determines the sidetracking success or not. The mill will be subject to the force of casing, coiled tubing and rock. So, it is significant to comprehensively analyze the force on the mill. According to the practical requirements, this paper is set in casing sidetracking in OD139.7mm by coiled tubing to do the following research:(1) The studying of Coiled tubing sidetracking technology is strengthened. According to the feature of coiled tubing, I will thorough research on the process of coiled tubing sidetracking and analyze the technical difficulties, details dealing and related parameters of sidetracking. After learning foreign advanced technology, a process of coiled tubing sidetracking is designed.(2) Analyze parameters and mechanical properties of coiled tubing, casing and whipstock to choose the suitable research object. Focus on the research into different leading mill and reaming mill about their background, function, feature, number and so on. Through analyzing the relationship between the mills structure parameters and the torque, guidance, and aggression of the mills when sidetracking, the mills are designed to ensure their wear resistance and impact resistance for stable sidetracking.(3) Based on the sound assumption of drilling condition, the translation and rotation trajectory of the bits is simulated during milling by using the rigid model in the local and entire coordinate. The 3D solid model and physical models of two mills are established and the point distribution of the model is designed to analyze the contact area and force between mills and casing. The torque on the BHA and window shapes is analyzed when they are milling along the trajectory. A better sidetracking program is designed by changing the whipstock.The results demonstrate that the success of sidetracking depends on grasping the details in the process of coiled-tubing sidetracking. Reasonably designing the structure parameters of the sidetracking tools can help us reduce the damage on the whipstock and maintain a stable operation. According to the torque changing of the mill, at the beginning the torque is very large. Along with the moving of the mill, torque reduces obviously then tends to be stable. According to this regular, we find that it is effective to reduce torque on BHA by changing the build-up rate in the upper of the whipstock. At the same time, through comparing the window shapes, which are before and after the adjustment, the feasibility of the scheme is verified. To increase the length of the active window, a vertical plane is added at the location of grinding the window with the maximum width. Finally we get a complete multiple inclined plane whipstock. This whipstock can help us reducing the incipient torque, increasing the length of the active window and saving time. It is significant in conducting field operation.