## 5 Conclusions  
The experimental stand, developed at the St. Petersburg Mining University, is an innovative solution in the field of improving the quality of cleaning directional wells. This study is fundamental, since for the first time the issue of the positive aspect of the loss of stability of the DS was considered, and the positive effect of pipe buckling on the efficiency of cuttings removal was established, taking into account the drilling parameters, technological and rheological properties of the drilling rig, and the angle of inclination of the well.  
The analysis of well cleaning quality data, depending on the zenith angle \(\alpha\), confirms the presence of a critical angle \(\alpha=55^{\circ}\) in the zone with a range of 45-60\({}^{\circ}\), in which the maximum difficulty is noted in the transport of cuttings particles to the day surface--a decrease in the removal of particles to 40-60%.  
When conducting a series of experiments No. 1 with a Newtonian liquid, an increase in the efficiency of mud removal by up to eight times was found, at the maximum flow rate of the BR, the rotation frequency \(n=0.83\div 2.50\) s\({}^{-1}\) and the presence of three half  
Figure 7: Conceptual diagram of the location of FBG strain sensors in the body pipes on the inner wall (**a**) and in the outer wall (**b**).  
waves string, in comparison with straight DS and strings with the first half-wave. When conducting a series of experiments No. 2 and using a pseudo-plastic liquid as mud, all other things being equal, an increase in the removal of mud cuttings up to 36% was found.  
It has been experimentally established that, when the string rotates at a speed of \(n=0.83\div 2.50\) s\({}^{-1}\), at a flow rate \(Q=1.25\times 10^{-3}\) m\({}^{3}\)/s of a pseudo-plastic liquid with rheological properties, the removal of mud cuttings to the surface increases dozens of times in comparison with the Newtonian fluid.  
The authors put forward a hypothesis that the controlled buckling of the string, namely, the number and length of half-waves in the place specified by the operator, allows the breakdown of mud plugs and improves well cleaning, as well as solving the problem of \"mud-pads\" and the complications and emergencies associated with this phenomenon.  
The presented technical and technological solution for the implementation of a hydromechanical method for the destruction of stagnant mud zones is a novel concept and requires further study with the subsequent development of experimental drill pipes based on FBG strain sensors.  
The obtained results confirm the need for further study of the effect of pipe buckling on the destruction of mud plugs and cleaning of deviated wells from cuttings, taking into account the multifactorial nature of the drilling process.  
Conceptualization, V.G.K. and M.V.D.; methodology, V.G.K. and M.V.D.; software, V.G.K.; validation, V.G.K. and M.V.D.; formal analysis, V.G.K. and M.V.D.; investigation, V.G.K. and M.V.D.; resources, M.V.D.; data curation, M.V.D.; writing--original draft preparation, V.G.K.; writing--review and editing, M.V.D.; visualization, V.G.K.; supervision, M.V.D.; project administration, M.V.D.; funding acquisition, V.G.K. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
All the data used in this study are available in the article.  
The authors are grateful to [PERSON], Chief Specialist of Well Construction Laboratory, for his help in designing experimental equipment and support during the research.  
The authors declare no conflict of interest.