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Abstract
Coiled tubing drilling has become an important development direction of drilling. The method of combining theoretical calculation with the experimental verification is adopted to analyze the flow of the coiled tubing drilling system. A set of experimental bench is developed, three kinds of curvature ratio of coiled tubing are used, and the frictional pressure losses of coiled tubing and partial pressure drop of each downhole tool are tested. The results of experiments with water agree well with rough pipe calculation model. The pressure losses of coiled tube are obviously larger than that of straight tube, and the value of it is about 11–17%. The larger the curvature ratio is, the more the pressure losses of coiled tubing are. The fluid experiment with the polymer presents obviously the drag reduction effect. Experiment of simulated bottom hole assembly shows that partial pressure drop of bottom hole assembly is large. It has a little effect on the pressure losses of coiled tubing when whole bottom hole assemblies are connected. The research results can be used as the basis for formulating coiled tubing drilling process parameters, which will provide a guide for engineering practice.
Highlights
Coiled tubing unit (CTU), playing an increasingly important role in exploration and development of oil and gas, has been widely applied in oil and gas project including servicing, drilling, completion, and logging
The experimental results show that the Colebrook-White rough pipe calculation model is closer to reality under the working condition of Coiled tubing drilling (CTD)
Considering the difference of curvature ratio (CR) caused by different number of layers of coiled tube, the difference of pressure losses of CT is very small, so pressure losses of CT with the smallest value of CR can be the basis of calculating drilling process parameters
Summary
Coiled tubing unit (CTU), playing an increasingly important role in exploration and development of oil and gas, has been widely applied in oil and gas project including servicing, drilling, completion, and logging. Medjani and Shah [3] studied the influence factors about frictional pressure losses of three kinds of polymer with different concentrations and obtained the frictional pressure losses correlations which can be applicable to several kinds of fluid through fitting experimental data according to the power-law regression. Shah and Kamel [11] made the research about investigation of flow behavior of slick-water in large straight and coiled tubing; curvature of CT and roughness affect drag reduction characteristics of this polymeric fracturing fluid significantly. Ogugbue and Shah [12] presented the results of an experimental study carried out to investigate frictional pressure losses behavior of drag reducing polymer solutions, flowing turbulently through an eccentric annulus. The research results in this paper can be used as the basis for formulating process parameters of CTD, which will provide a guide for engineering practice
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