Известия Томского политехнического университета: Инжиниринг георесурсов (Dec 2020)
RESEARCH OF POWER IMPULSES TRANSFER THROUGH THREADED CONNECTIONS OF THE DRILL-STRING DURING ROTARY-PERCUSSION DRILLING OF PILOT HOLES FOR TRENCHLESS PIPELINE LAYING
Abstract
The relevance of the research. Pilot wells for horizontal directional drilling can be attributed to slim holes that are widely used in mining, in particular, for detailed exploration and underground development of non-ferrous metal ores, for degassing mine workings of coal mines, as well as in a lot of other industries to limit the diameter of a hole due to technological or technical conditions. Moreover, to obtain effective drilling of slim holes in rocks with high alteration in hardness, drilling rigs are equipped with percussion mechanisms forming force impulses in a drill-string in the form of elastic deformation waves propagating at sound speed through drill pipes threaded connections towards a rock-breaking tool. Such energy transfer of power impulses is accompanied by its dissipation in the threaded connections. Thereat if the connections of drill pipes are intended only for rotary drilling the energy loss of power impulses in them may be unacceptably large, and efficiency and strength are significantly reduced. Though the threaded connections are considered to be stationary, in reality while simultaneous loading of them by torque, drilling tool feed thrust and power impulses a small slip inevitably arises on the contact surfaces of the elements of drill pipes connections. Friction force works on this relative travel causing energy loss that can be quantified experimentally. Without a clear understanding of the rules of power impulses propagation through threaded connections, it is impossible to assess objectively the possibilities of the efficiency increase of the transfer of their energy on a drill-string to the rock-breaking tool, and therefore, in general at all, the reasonableness of using percussion mechanisms in installations for horizontally directed drilling of pilot wells. Thus, the scientific substantiation and development of recommendations for designing and creating new designs of threaded connections of the drill-strings to improve the efficiency of the rotary-percussion method of drilling slim holes are the urgent scientific and technical task. The aim of the research is to analyze the dynamic processes in the threaded connections of a drill-string during the transfer of the power impulses from the percussion node to the rock-breaking tool;to build hysteresis diagrams which allow assessing the energy loss associated with the work of inelastic resistance force at the contact places of the mated parts of the threaded connections during the propagation of the power impulses through them based on the experiments performed;to show by examples the futility of attempts to achieve the effective transfer of the power impulses through the connections of the drill pipes that are used for rotary drilling and to substantiate the recommendations on the development of fundamentally new nipple connections of the pipes proposed by the National Research Tomsk Polytechnic University for drilling the pilot wells that have previously successfully passed production tests at non-ferrous metallurgy mines in Kyrgyzstan and Kazakhstan with the direct participation of the authors in the rotary-percussion drilling of slim holes from underground mine workings. The object of this study is drill-strings with coupling and nipple connections, used in the rotary-percussion method of drilling wells, as well as the threaded connections of the pipes for the pilot wells for horizontal directional drilling. Methodology: the review of scientific literature on formation of the percussion impulses, the transfer of the waves of deformation on a drill-string; the substantiation of the use of the rotary-percussion method of drilling for horizontal directional drilling as well as the comparison of research results and the assessment of energy friction loss in the threaded connections of the drill pipes. Findings. Based on the percussion-wave theory previously unknown interrelations were obtained which allowed running the computer simulation of threaded connections parameters influence on the efficiency of the power impulses transfer on a drill-string. The main cause of impulses energy loss was found to be the forces of inelastic resistance occurring in case of the relative displacement of the drill pipes and the connecting elements. To increase the transfer ratio of the amplitude of the power and the energy of the impulses it is necessary to take the minimum possible value of connecting element rigidity as well as to increase the contact stiffness of the conjugate turns of the threaded connection. Currently used drill pipes connections for horizontal directional drilling of wells are not suitable for rotary-percussion drilling due to the reflection of the waves of deformation from the sections of the threaded connections of the drill pipes without connecting elements (couplings or special closed-type nipples).
Keywords
