| Recently,as China’s highway and railway construction has progressed quickly,the number and length of tunnels are also growing rapidly.Specifically,China ’s western development strategy has entered a stage of accelerated development,and the amount of long tunnel building growing yearly in the mountainous southwest of the country.The safety risk of tunnel construction is extremely high if the geological conditions of the tunnel excavation line are unclear.Accidents like tunnel water gushing,mud gushing,and even collapse are likely to occur,causing the construction of the tunnel to be stopped and resulting in significant financial losses or human casualties.Therefore,it is very necessary to investigate the tunnel accurately before the design and construction.The horizontal or near-horizontal exploration hole along the tunnel axis is a more effective way to explore the engineering geological conditions along the tunnel than the traditional vertical hole geological exploration technology.It can obtain the accurate geological conditions of the tunnel extension line,reduce the need for road construction,and be environmentally friendly.Nonetheless,the drilling tool’s gravity direction is 90 degrees from the drilling direction because to the horizontal hole drilling.In order to increase the drill string’s axial resistance and circumferential torque,the drilling rig must apply feed pressure,the drill string and hole wall have a broad contact area,there are numerous cuttings in the hole,and the hole wall is not stable.The drilling tool’s complicated movement form,the drill pipe’s easy bending and breaking,the drilling’s easy deflection,the construction’s increased difficulty,and the insufficient drilling pressure at the hole’s bottom limit the drilling depth and make it unable to satisfy the geological exploration requirements set forth by the tunnel design department.Therefore,this paper investigates the drag of the wire-line coring drill string in the horizontal exploration hole,so as to optimize the drill string structure and drilling parameters,decrease the drill string drag in the horizontal exploration hole,increase the drilling depth,and satisfy the needs of engineering exploration.In order to further study the axial resistance and circumferential torque of the horizontal exploration hole drill string and solve the scientific problems of the horizontal exploration hole drilling technology,this paper analyzes the drill string dynamics of the horizontal exploration hole through theoretical research,uses LSDYNA software to numerically simulate the friction of the horizontal exploration hole drill string,and conducts indoor simulation drilling test through the horizontal exploration hole wire-line coring drilling simulation test platform.The friction change of drill string under different conditions was studied,and the influence of feed pressure,rotation speed,drill pipe structure and drilling fluid on the drag of drill string in horizontal exploration hole was explored.The research results obtained are as follows :(1)Based on the finite element equation established by the finite element method,the dynamic contact model established by the momentum theorem and the momentum moment theorem,and the calculation model of the drilling fluid force obtained by the force analysis of the isolation method,the dynamic mathematical model of the drill string in the horizontal exploration hole is determined.The force and motion state of the drill string in the horizontal exploration hole are analyzed,and the finite element equation is established by using the space beam element.The dynamic contact model between the drill string and the hole wall and the calculation model of drilling fluid force are given.The mathematical model of drill string dynamics with high nonlinearity is obtained,and the equation solving process is given.(2)By using LS-DYNA software,the effects of feeding pressure and rotational speed on the drag of drill string are revealed through numerical simulation.The geometric model of diamond wire-line coring drill string drilling system in horizontal exploration hole is established by using Solidworks software.Through numerical simulation,it is concluded that : with the increase of the feed pressure,the axial resistance of the drill string increases,the circumferential torque of the drill pipe increases,and the circumferential torque of the drill bit increases linearly,but becomes a small amplitude stable fluctuation after the feed pressure reaches the threshold value.The rotational speed mainly affects the circumferential torque of the drill string.As the rotational speed increases,the axial resistance of the drill pipe and the amplitude of the circumferential torque fluctuation decrease.The axial resistance of the drill bit is in a regular and stable fluctuation,while the circumferential torque curve increases.It is concluded that increasing the rotational speed will reduce the feed pressure threshold of the bit breaking rock.(3)Through numerical simulation,the influence of drill pipe structure on drill string drag is revealed,and it is concluded that the drill pipe structure with flat end and large annular clearance can reduce the drill string drag.The drill pipe structure is changed from the following three aspects : the end structure is changed from the flat end to the thickened end,the annular clearance is changed from 2.5 mm to 3.5 mm and4.5 mm,and the single length is changed from 3 m to 4.5 m and 6 m.The numerical simulation results show that the contact force between the drill string and the hole wall will be increased due to the increase of the outer diameter of the drill pipe end,and the axial resistance and circumferential torque of the drill pipe will be increased by 20%-40% compared with the flat end.The large annular clearance drill string structure will reduce the contact force between the drill string and the hole wall,and significantly reduce the circumferential torque of the drill string.In particular,the axial resistance and circumferential torque of the drill pipe can be reduced by 10 % at least.The single length has little effect on the axial resistance and circumferential torque of the drill string,and the long drill pipe increases the axial resistance and circumferential torque of the drill string by 3 %-5 %.(4)A simulation test platform for wire-line coring drilling in horizontal exploration holes was developed,and the friction of drill string was tested.The influence of drilling fluid on drill string was revealed,and the research results of numerical simulation were verified.According to the similarity principle,the similarity criterion equation is derived by dimensional analysis method,and then the geometric similarity ratio of the model and the structural parameters of the test bench are determined by geometric similarity and physical similarity.From the indoor simulation drilling test,it is concluded that the influence of feed pressure and rotational speed on the friction of drill string is the same as that of numerical simulation.The drilling fluid has viscous resistance to the drill string,which leads to the increase of the axial resistance and circumferential torque of the drill string.The drilling fluid flow rate has little effect on the axial resistance of the drill string,but the buoyancy of the drilling fluid will balance the gravity of a part of the drill string,reduce the contact force between the drill string and the hole wall,and reduce the circumferential torque of the drill string.When the rotation speed is large,the circumferential torque tends to be stable after the drilling fluid flow reaches a certain value. |
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