Research On Flow Characteristic Of Coiled Tubing Drilling System

Coiled Tubing is called Flexible Tubing in the industry. In the Second World War, Coiled Tubing began to appear in industrial applications. Since the 1960s, the oil industry is gradually noticed it. So far the Coiled Tubing has a history of 50 years. Application and development of Coiled Tubing Drilling (referred to as CTD) technology began in the 1990s.With the Coiled Tubing in oil drilling application, Coiled Tubing due to the need in the practical application to complete a series of size changes. Its size gradually increases. Initially experts predict Coiled Tubing Drilling technology may be limited to use in vertical well drilling. But with the development of Coiled Tubing Drilling technology, people cannot even imagine that CTD can be applied to directional and horizontal wells. In the social situation of the sharp increase in the cost of drilling and oil prices fell, reduce drilling costs and improve drilling efficiency is the only way out of the dilemma of the petroleum industry at present. So the future of the oil industry of Coiled Tubing Drilling market will be growing. The number of CTD also increased substantially. At the time of the late 1850s, advanced researchers has developed Coiled Tubing Drilling through continuous exploration. However, due to its ability to adapt to the difference and the reason for Coiled Tubing Drilling technology supporting facilities, making the Coiled Tubing Drilling technology until the 1990s began to really enter the oil drilling industry.Up to now, Coiled Tubing Drilling in the application of the oil industry are:drilling new wells, old wells deepened, side-tracking horizontal well in old wells, directional drilling, under balanced Coiled Tubing Drilling and so on. Fluid flow accompanied by a large linear loss along the tube inside coiled tubing. In particular, due to different circumstances lead to helical bucking fluid by changing the centrifugal force, the fluid will occur secondary flow phenomena when flows through the spiral section. This time there will be a lot of resistance to fluid loss. Therefore, we have to figure out the Coiled Tubing Drilling pipe flow characteristics. This design of the pump power, computing buttonhole pressure, maximum wellhead pressure has important significance when CTD work. So research on the flow of Coiled Tubing system have unprecedented significance.Based on previous researches, this paper combines three different methods of combining comparative analysis, including theoretical model, experiments and numerical simulation of coiled tubing drilling system. This paper main significance include:firstly, through experiments analyzed the flow characteristics within the coiled tubing pipe. It would be compared with the theoretical model. Final verify the correctness and applicability of the theoretical model. Secondly, On the basis of numerical simulation within Coiled Tubing Pipe. Combined it with theoretical model calculations to correct and improve the numerical simulation model. Finally, on the basis of experimental data in CTD system to correct and improve theoretical models and numerical simulation models.The dissertation completed the theoretical model analysis and numerical simulation analysis. We completed downhole tool flow experiments. It was considered that different fluids, different coil specifications in experiments. Companied with theoretical calculations, experimental results and numerical results of system, the following conclusions was as follows:Firstly, comprehensive analysis of the theoretical calculation in the various parts of coiled tubing drilling system models. Based on this we propose a set of theoretical system model.Secondly, through the coil segment Newtonian and non-Newtonian fluids numerical simulation calculations. By analyzing four kinds of numerical model, the K-epsilon model was selected. Considering the impact of rough thickness to use this model for numerical simulation. Model results was compared with theoretical calculations, the accuracy and applicability of the model to be verified.Thirdly, model comparison of 4 kinds media, three kinds of drum specifications and consider simulate downhole tool combination. In this model the experimental research of drilling systems simulate continuous flow tube, the following conclusions can be obtained:1) When the fluid flow in the coil, the coil curvature does have a certain influence on the pressure loss. But within a certain range, the curvature has little effect on the loss of coiled tubing fluid friction.2) With the addition of polymer during the coiled tubing test fluid flow experiments presented in the drag reduction, the xanthan glue and the other two drilling fluids have both been strong drag reduction phenomenon.3) When the downhole tool combination full connected or not, the changes was little of the actual continuous flow tubing pressure loss.4) Based on theoretical calculations and experimental results for comparison, when using Newtonian flow in coiled tubing drilling, we conclusion that the Colebrook-White rough tube model was closer to the actual. For non-Newtonian flow, the drag reduction curve must be used in specific flowing medium. Otherwise theoretical calculation model was significantly larger, not applicable for actual working conditions.5) Through the numerical simulation and experimental results, the following conclusions can be gotten of the calculation for coiled tubing pipe section helical buckling. Compared with the coil, helical buckling pipe pressure loss was significantly larger. In the case of the same size pitch, the smaller of radial clearance for tubing and casing, the greater the pressure loss.