OPTIMIZATION AND ANALYSIS OF MECHANICAL STRUCTURE OF DOWNHOLE REVERSAL CONTROL SUB-SECTIONS IN COILED TUBE DRILLING

Complex oil drilling operations will delay the drilling cycle. Coiled tube drilling technology is currently an effective way to increase the ROP and speed up the drilling progress. The downhole drilling tool assembly is a key component to control the well-bore trajectory and wellbore structure. Therefore, the systematic analysis and design of the downhole reversal control sub-section is of great significance to the smooth development of drilling operations. In this paper, a mechanical analysis model for the reverse short section of coiled tube downhole drilling operations is constructed. In addition, the factors affecting the short section were analyzed, and finally the structure of the short section was optimized to facilitate the normal construction of coiled tube drilling operations. The research results show that the frictional force of the friction block on the borehole wall during the drilling process will increase rapidly as the pressure of the drilling fluid increases. However, the frictional force of the friction block on the borehole wall does not increase linearly with the increase of drilling fluid pressure. During the drilling process, the friction force generated by the friction block on the borehole wall increases linearly with the gradual increase of the friction coefficient of the friction block, and the increase is maintained at a level of 8.0 KN for every increase of the friction coefficient by 0.1. To achieve the maximum thrust of the palm during drilling 17.53 KN, the design values of the three parameters h(1), h(2) and h(3) of the friction block when the friction coefficient is 0.4 should be designed as h(1) =23 mm, h(2) =10 mm and h(3) =25 mm, respectively.